Method and apparatus for separating CO2 from at least two streams with different compositions

Abstract

Title: Method and apparatus for separating CO2 from at least two streams with different compositions In an integrated separation process, a first flow (1) containing a first percentage of CO2 is compressed (1C), separated in a pre-concentration unit (P), producing a gas (11) enriched in CO2 and depleted in oxygen compared to the first flow and the gas enriched in CO2 is separated (1F) producing a fluid containing at least 95 mol% CO2(19) and at least a first fluid depleted in CO2 (15, 17), a second flow (2) contains a second percentage of CO2 greater than the first percentage, the second flow is compressed (2C), dried in a second drying unit (2D), separated by partial condensation and / or by distillation in a second separation unit (2F, 2G),the second separation unit producing a CO2-enriched fluid (119) containing at least 90 mol% CO2 and depleted in oxygen as well as a second CO2-depleted and oxygen-enriched fluid (121) and to recover the CO2 present in the second CO2-depleted fluid, the latter is sent at least partly upstream of the pre-concentration unit. Abstract figure: Fig. 1,

Description

Title of the invention: Method and apparatus for separating CO2 from at least two streams with different compositions

[0001] The present invention relates to a method and apparatus for separating CO2 from at least two streams with different dry-based CO2 compositions.

[0002] At least one of the streams contains less than 50 mol% of CO2 on a dry basis, preferably less than 30 mol% of CO2 on a dry basis, or even less than 20 mol% of CO2 on a dry basis and at least one other of the streams contains more than 50 mol% of CO2 on a dry basis.

[0003] For example, at least one of the streams contains less than 25 mol% CO2 on a dry basis and at least one other of the streams contains more than 90 mol% CO2 on a dry basis.

[0004] Streams with different CO2 compositions are found in many processes. Streams with high CO2 concentrations are often produced by well-known units, such as an amine scrubber on synthesis gas to remove CO2 upstream of a cryogenic carbon monoxide separation.

[0005] High concentration streams are also produced by technologies operating on flue gases, such as amine washing or are produced directly by the upstream process by partial or complete oxycombustion.

[0006] At the same time as high concentration streams are produced, streams containing less CO2 than these are often available in the same geographical area or industrial process.

[0007] The following examples can be cited:

[0008] [Tab 1] More concentrated stream (% mol CO2 dry basis) Less concentrated stream (% mol CO2 dry basis) SMR Amine wash sized by available residual heat (>95%) Gas sent to stack by SMR (15%-25%) Refinery Amine wash (>95%) Fluidized catalytic cracking (FCC) tail gas (15%-25%) Or Reheat furnace (10-20%CO2) Cement plant Amine wash sized by available residual heat (>95%) - Oxy-fuel combustion for pre- Main stack (15%-35%) Dedicated stack for rotary kiln (10%-25%) Calciner / separate calciner or not (>60%) - Calix process (>90%) Lime plant Oxy-combustion with parallel flow regenerative kiln (PRFK) (>60%) Parallel flow regenerative kiln with cooling air extraction (>40%) Rotary drum kiln, axial kiln or PRFK stack (15%-25%) Steel mill Amine scrubbing of DRI reactor gas (>95%) or other steel mill gas (e.g. blast furnace gas) PSA residue on blast furnace gas Fuel heating waste gas (15%-30%) Or blast furnace gas (15-30%)

[0009]

[0010]

[0011]

[0012]

[0013]

[0014] The above examples are not exhaustive and can even be crossed in an industrial basin (for example a flow coming from a cement plant, another coming from a lime factory or an SMR...) Streams with different CO2 concentrations can be treated by pooling certain parts of the treatment, preferably allowing CO2 recovery rates of more than 92 mol%, or even more than 95 mol% for low concentration streams and rates of up to 99 mol% for high concentration sources. For example, for a gaseous CO2 source containing 15-25 mol% CO2 from a stack and a gaseous CO2 source containing more than 95 mol% CO2 from an amine scrubber, the gas containing between 15 and 25 mol% CO2 can be scrubbed by adsorption ((V)PSA), permeation, partial condensation and / or distillation to form a CO2-enriched gas and: • CO2-enriched gas and gas containing more than 95%mol of CO2 can be compressed together, the gas containing more than 95% mol having been dried upstream of the common compression, • CO2-enriched gas and gas containing more than 95%mol of CO2 can be compressed and dried together. Gas containing 15-25 mol% CO2 can be separated by partial condensation and / or distillation to produce a liquid. At the same time the gas produced by amine washing can be liquefied independently during.

[0015] The gas containing 15-25 mol% CO2 can be separated by adsorption ((V)PSA), permeation, partial condensation and / or distillation to produce a CO2-enriched gas which is liquefied in the same liquefier as the gas produced by amine scrubbing.

[0016] Alternatively the gas produced by amine washing can be dried and compressed and then sent to the partial condensation and / or distillation step fed with the gas containing 15-25 mol% CO2 to produce a common flow of liquid CO2.

[0017] For example, the gas containing 15-25 mol% CO2 can be a residual gas from SMR and the gas containing more than 95 mol% CO2 can be produced by amine scrubbing installed on the synthesis gas (typically upstream of cryogenic CO capture).

[0018] For other applications, CO2-containing streams may be co-produced by oxycombustion and air combustion. In this case, oxycombustion produces a gas stream containing 50-97 mol% CO2 while air combustion produces a gas stream containing between 15-35 mol% CO2.

[0019] Each flow can be treated independently to produce two CO2-enriched gaseous products.

[0020] Otherwise the two independently treated flows can be compressed by a common compressor forming a single gas flow under pressure.

[0021] Alternatively each flow can be treated independently to produce two CO2-enriched gaseous products and the two gaseous products can be liquefied in a common liquefier.

[0022] According to the invention, an integrated method is proposed which is of particular interest for the case where two flows are produced, a first flow containing a first percentage of CO2 and the second flow containing a second percentage of CO2 greater than the first percentage.

[0023] It applies to the case where the first flow is separated in a preconcentration unit, for example pre-concentration by adsorption in an adsorption unit, producing a gas enriched in CO2 compared to the first flow and the gas enriched in CO2 is separated by partial condensation and / or by distillation.

[0024] The second flow is separated by partial condensation and / or distillation, producing a CO2-enriched fluid and a CO2-depleted fluid. To recover the CO2 present in the CO2-depleted fluid, it is recycled to be separated in the preconcentration unit used to separate the first flow.

[0025] This brings significant advantages, by allowing to increase the overall CO2 yield. In addition, it allows to reduce the cost of the installation by eliminating the membranes or the dedicated CO2 PSA usually used to recover the CO2 in the CO2-depleted fluid. It becomes possible to use a unit downstream of the recycle to the preconcentration unit operating at low temperature to separate by partial condensation and / or distillation to produce a fluid containing at least 90% mol CO2 whereas usually such concentrations are not achievable with good efficiency.

[0026] According to an object of the invention, an integrated separation process is provided in which:

[0027] i) a first flow containing a first percentage of CO2 as well as oxygen and optionally water is compressed, optionally dried in a first drying unit, separated in a pre-concentration unit, for example by adsorption in an adsorption unit, producing a gas enriched in CO2 and depleted in oxygen compared to the first flow and the gas enriched in CO2 is separated by partial condensation and / or by distillation and / or by solidification in a first separation unit producing a fluid containing at least 95 mol% CO2 and at least a first fluid depleted in CO2,

[0028] ii) a second flow contains a second percentage of CO2 greater than the first percentage as well as oxygen and water, the second flow is compressed, dried in a second drying unit, separated by partial condensation and / or by distillation and / or by solidification in a second separation unit, the second separation unit producing a CO2-enriched fluid containing at least 90 mol% of CO2 and depleted in oxygen as well as a second CO2-depleted and oxygen-enriched fluid, and

[0029] iii) to recover the CO2 present in the second fluid depleted in CO2, the latter is sent at least in part

[0030] a. upstream of the pre-concentration unit and / or,

[0031] b. downstream of the pre-concentration unit.

[0032] According to other optional aspects: • the second fluid depleted in CO2 is separated in the preconcentration unit. • the first and / or second flow contains nitrogen, nitrogen oxide or carbon monoxide. • the pre-concentration unit separates the first flow, and possibly the second fluid depleted in CO2, by adsorption, for example by pressure shift, or by permeation. • the first flow contains less than 50% mol CO2 on a dry basis, preferably less than 35% or even less than 30% mol CO2 on a dry basis. • the CO2-enriched gas contains more than 50% mol CO2 on a dry basis, preferably more than 90% mol CO2 on a dry basis. • the second flow contains at least 50% mol CO2 on a dry basis, more than 70% mol CO2 on a dry basis, or even at least 90% CO2 on a dry basis. • the difference between the first percentage and the second percentage of CO2 on a dry basis is at least 20%, or even at least 40%. • the second flow is dried, for example at compressed atmospheric pressure, and then separated in the first or second separation unit. • the second fluid depleted in CO2 is sent at least in part

[0033] upstream of the pre-concentration unit, possibly by mixing it directly with the first flow, and the gas enriched in CO2 contains less of the lighter constituent than a residual gas from the pre-concentration unit. • the second CO2-depleted fluid is sent at least in part to be mixed under pressure with the CO2-enriched gas coming from the preconcentration unit after at least one step of compression of the CO2-enriched gas. • the first fluid depleted in CO2 is mixed with the second fluid depleted in CO2. • a gaseous mixture formed by mixing the first and second CO2-depleted fluids is expanded in a turbine. • a gas mixture formed by mixing the first and second CO2-depleted fluids serves as regeneration gas in the preconcentration unit which operates by adsorption. • a fluid containing at least 95% mol CO2 from the first separation unit is sent to the second separation unit. • the second fluid depleted in CO2 and enriched in oxygen is separated in the first separation unit. • the second fluid depleted in CO2 and enriched in oxygen is mixed and compressed with a gas to be separated in the first separation unit. • the second fluid depleted in CO2 and enriched in oxygen is mixed and compressed with the gas enriched in CO2 and depleted in oxygen to be separated in the first separation unit. • the second fluid depleted in CO2 and enriched in oxygen is mixed with the compressed gas enriched in CO2 and depleted in oxygen to be separated in the first separation unit. • the second fluid depleted in CO2 and enriched in oxygen is mixed with a separated gas in the first separation unit.

[0034] According to another object of the invention, there is provided an integrated separation apparatus comprising a first compressor, possibly a first drying unit, a pre-concentration unit, for example by adsorption in an adsorption unit, a first separation unit, means for sending a first flow containing a first percentage of CO2 as well as oxygen and possibly water to the compressor to be compressed, possibly means for sending the first compressed flow to be dried in the first drying unit, means for sending the first compressed and possibly dried flow to separate in the pre-concentration unit, producing a gas enriched in CO2 and depleted in oxygen compared to the first flow, means for sending the CO2-enriched gas (13) to be separated by partial condensation and / or by distillation and / or by solidification in the first separation unit producing a fluid containing at least 95 mol% CO2 and at least a first fluid depleted in CO2, a second compressor, a second drying unit,a second separation unit by partial condensation and / or distillation, means for sending a second flow containing a second percentage of CO2 greater than the first percentage as well as oxygen and water to the second compressor to be compressed, means for sending the second compressed flow to be dried in the second drying unit, means for sending the second compressed and dried flow to be separated by partial condensation and / or by distillation and / or by solidification in the second separation unit, the second separation unit producing a CO2-enriched fluid containing at least 90 mol% of CO2 and depleted in oxygen as well as a second CO2-depleted and oxygen-enriched fluid and means for sending the second fluid depleted in CO2 at least in part,

[0035] a. upstream of the pre-concentration unit and / or

[0036] b. downstream of the pre-concentration unit.

[0037] to recover the CO2 present in the second CO2-depleted fluid.

[0038] Preferably, the apparatus does not comprise a first drying unit.

[0039] The apparatus does not include a preconcentration unit between the second compressor and the second drying unit.

[0040] The apparatus does not comprise a preconcentration unit between the second drying unit and the second partial condensation and / or distillation separation unit.

[0041] The second separation unit may comprise at least one phase separator upstream of at least one distillation column, the second CO2-depleted fluid coming from the at least one phase separator and the CO2-rich product coming from the at least one distillation column.

[0042] Among the optional features of the invention: • the first flow comes from a steel mill • the first flow is a waste gas from fuel heating, for example from a steelworks • the first flow is blast furnace gas • the first flow comes from a lime factory • the first flow comes from a rotary drum kiln, an axial kiln or a FRP chimney of a lime factory • the first flow comes from a cement plant • the first flow comes from the main chimney of a cement plant or from the chimney dedicated to the rotary kiln of a cement plant or a lime factory • the first flow comes from a refinery • the first flow is a residual gas from fluidized bed catalytic cracking or comes from a refinery reheating furnace • the first flow is a gas sent to the chimney of an SMR • the first flow contains on a dry basis between 15 and 25% mol of CO2, between 10 and 20 mol% CO2, between 15 and 35 mol% CO2, between 10 and 25% CO2 • The second flow contains on a dry basis more than 90% mol of CO2, or even more than 95% mol of CO2 • The second flow comes from an amine wash, for example treating a gas from a refinery or reformer or a cement plant or a steel mill (for example DRI reactor gas or blast furnace gas). • the second flow comes from oxycombustion, for example from oxycombustion from a lime plant for precalciner or calciner • the second flow comes from a Calix process • the second flow is a PSA waste product having separated, for example, a blast furnace gas • the second flow comes from a lime factory • the second flow comes from an oxycombustion with a regenerative flow furnace parallels (PRFK) • the first flow comes from a parallel flow regenerative furnace with extraction of cooling air • the first and second flows both come from the same steel mill, the same lime plant, the same cement plant, the same refinery or the same reformer (for example SMR). • the first and second flows both come from different processes operated within the same steelworks, the same lime plant, the same cement plant, the same refinery or the same reformer (for example SMR). • both the first and second flows come from a steel mill, a lime plant, a cement plant, a refinery or a reformer (for example example SMR). • the first flow comes from a steel mill or a lime plant or a cement plant or a refinery or a reformer (e.g. SMR) and the second gas comes from another unit which is a steel mill or a lime plant or a cement plant or a refinery or a reformer (e.g. SMR).

[0043] The invention will be described in more detail with reference to the figures in which:

[0044] [Fig-1] illustrates a method according to the invention.

[0045] [Fig.2] illustrates a method according to the invention which is a variant of that of [Fig.l]

[0046] [Fig.3] illustrates a method according to the invention.

[0047] [Fig.4] illustrates a method according to the invention.

[0048] [Fig.l] illustrates a method according to the invention in which a first flow 1 containing less than 50% mol CO2 on a dry basis, for example between 15 and 25% mol CO2 on a dry basis is separated in a first apparatus A ending with a partial condensation and / or distillation step to produce a fluid, here a liquid containing at least 95% CO2.

[0049] The first apparatus A comprises a compressor IC, a drying unit 1D, a pre-concentration unit P, a compressor 1E and a partial condensation and / or distillation separation unit 1F. The drying unit D can be integrated into the pre-concentration unit P.

[0050] The first flow 1 also comprises oxygen, water and optionally at least one component which is nitrogen, nitrogen oxide or carbon monoxide.

[0051] The first gas may come from • a steelworks, • a lime factory, • a cement plant, • a refinery.

[0052] The first gas may be a waste gas from fuel heating, for example from a steelworks, a blast furnace gas

[0053] The first gas may come from a rotary drum kiln, an axial kiln or a PRFK chimney of a lime plant.

[0054] The first gas may come from a rotary drum kiln of a cement plant.

[0055] The first gas may come from the main chimney of a cement plant or from the chimney dedicated to the rotary kiln of a cement plant or a lime factory.

[0056] The first gas may be a residual gas from fluidized bed catalytic cracking or comes from a reheat furnace of a refinery.

[0057] The first gas may be a gas sent to the stack of an SMR.

[0058] The first gas contains on a dry basis between 15 and 25 mol% of CO2, between 10 and 20 mol% of CO2, between 15 and 35 mol% of CO2, between 10 and 25% of CO2.

[0059] The first flow 1 is compressed by the compressor IC and dried in the drying unit 1D. The condensed water 5 in the compressor IC and the water 7 removed in the drying unit 1D are removed as condensate 9.

[0060] The first compressed and dried flow 10 is separated in the preconcentration unit P, which can operate by adsorption, for example by pressure shift or by permeation. The first flow 10 is separated forming a gas 11 enriched in CO2 and depleted in oxygen compared to the first flow. In the case of separation by adsorption, this gas 11 constitutes the waste product at low pressure. The gas 11 enriched in CO2 is compressed in a compressor 1E forming a compressed CO2-enriched gas 13 which is separated by partial condensation and / or by distillation and / or by solidification in a first separation unit 1F producing a fluid 19 containing at least 95 mol% CO2 as product.

[0061] A second flow 2 comprises at least 50 mol% CO2 on a dry basis, preferably at least 70 mol% CO2 on a dry basis and is separated in the apparatus B. It also comprises oxygen, water and optionally at least one component which is nitrogen, a nitrogen oxide or carbon monoxide. The second flow 2 contains in certain cases between 70 and 85 mol% of CO2 on a dry basis. The second flow 2 contains in certain cases at least 90%, or even at least 95 mol% of CO2 on a dry basis.

[0062] The second flow comes for example from an amine wash, for example treating a gas coming from a refinery or a reformer or a cement plant or a steelworks (for example DRI reactor gas or blast furnace gas).

[0063] The second gas comes for example from oxycombustion, for example from oxycombustion of a lime factory for precalciner or calciner

[0064] The second gas comes, for example, from a Calix process in a cement plant. This process works by heating the limestone via a special steel reactor. This separates and captures the pure CO2 as it is released from the limestone, and therefore keeps the exhaust gases from the kiln isolated.

[0065] The second gas may be a PSA waste product having separated, for example, a blast furnace gas.

[0066] The second gas may come from a lime factory.

[0067] The second gas can come from oxycombustion with a parallel flow regenerative furnace (PRFK).

[0068] The second gas can come from a parallel flow regenerative furnace with extraction of cooling air.

[0069] The first and second gases may both come from the same unit, which may be a steel mill, a lime plant, a cement plant, a refinery or a reformer (for example SMR).

[0070] The second flow 2 is compressed in a compressor 2C, condensing the water 105 it contains and the partially dried flow 102 is dried in a drying unit 2D, for example at atmospheric pressure, forming a dried flow 104 and water 107. The condensates 109 formed by mixing the flows 105, 107 are removed.

[0071] The second dried flow 104 is compressed in a compressor 2E and then sent as flow 113 to a unit for separation by partial condensation and / or distillation and / or by solidification 2F. A fluid 119, here liquid, is produced containing at least 90 mol% CO2. The unit 2F also produces a flow 121 depleted in CO2 and enriched in O2 which may for example come from at least one partial condensation separator upstream of at least one distillation column from which liquid CO2 119 is withdrawn. To recover the CO2 contained in the flow 121, it is sent to the pre-concentration unit P to separate there, preferably being mixed with the first flow 10.

[0072] In this case, membrane separation of the gas 121 is not necessary. Compressors 2C and 2E can be part of the same machine.

[0073] In [Fig.2], a variant of [Fig.l] is shown in which, rather than being injected directly upstream of the preconcentration unit P as in [Fig.l], the fluid 121 can be injected as flow 121A, 121B, 121C downstream of the latter, benefiting from the fact that the CO2-poor fluid 121 from the second unit 2F is typically at a pressure of around 30 bar. In this case, this fluid can be mixed after compression of the CO2-rich fluid from the preconcentration unit P or at the outlet of the low-temperature separation unit by partial condensation and / or distillation but before expansion in the turbine T.

[0074] Thus, the flow 121B depleted in CO2 and enriched in O2 coming from the unit 2F can be sent to mix with the gas 15 produced by the first separation unit 1F, the mixture then being expanded in a turbine T and sent to the preconcentration unit as regeneration gas.

[0075] Otherwise the flow 121C can be mixed with the feed flow 13 feeding the first separation unit 1F.

[0076] Otherwise the flow 121A can be compressed in the compressor 1E

[0077] In [Fig.3], apparatus A differs from that of [Fig.l] in that the fluid product 19 is a gas containing more than 80 mol% CO2, preferably at least 90% CO2. Apparatus B comprises two sections for separation by partial condensation and / or distillation and / or by solidification 2F, 2G, as well as possibly a unit M for separation by permeation.

[0078] Compressor 2E is not present.

[0079] The first section 2F separates the second compressed and dried flow 104 forming a gas flow 129 enriched in CO2 (containing more than 80 mol% of CO2, preferably at least 90% of CO2) and a flow 123 enriched in oxygen which can be separated by adsorption or permeation in the unit M to recover the CO2 which it contains.

[0080] Gas 129 and gas 19 from unit A are separated in the second section 2G by partial condensation and / or distillation forming a liquid 119 rich in CO2, for example containing at least 95% mol CO2. Section 2G produces an oxygen-enriched gas 121. Gas 123 and / or gas 121 is sent to the pre-concentration unit to be separated there.

[0081] [Fig.4] differs from [Fig.3] in that there is only one section for separation by partial condensation and / or distillation, which is section 2F and by the presence of compressor 2E. The gas 104 is compressed in compressor 2E, separated in section 2F forming a liquid 119 rich in CO2, section 2F also being supplied by gas 19 coming from apparatus A.

Claims

Claims

1. Integrated separation process in which i) a first flow (1) containing a first percentage of CO2 as well as oxygen and optionally water is compressed (IC), optionally dried in a first drying unit (1D), separated in a pre-concentration unit (P), for example by adsorption in an adsorption unit, producing a gas (11) enriched in CO2 and depleted in oxygen compared to the first flow and the CO2-enriched gas is separated by partial condensation and / or by distillation and / or by solidification in a first separation unit (1F) producing a fluid containing at least 95 mol% CO2 (19) and at least a first CO2-depleted fluid (15, 17) ii) a second flow (2) contains a second percentage of CO2 higher than the first percentage as well as oxygen and water, the second flow is compressed (2C), dried in a second drying unit (2D),separated by partial condensation and / or by distillation and / or by solidification in a second separation unit (2F, 2G), the second separation unit producing a CO2-enriched fluid (119) containing at least 90 mol% CO2 and depleted in oxygen as well as a second CO2-depleted and oxygen-enriched fluid (121, 121A, 121B, 121C) and iii) to recover the CO2 present in the second CO2-depleted fluid, the latter is sent at least in part a. upstream of the pre-concentration unit and / or b. downstream of the pre-concentration unit.,

2. A method according to claim 1 wherein the first and / or second flow (1,2) contains nitrogen, nitrogen oxide or carbon monoxide.

3. Method according to claim 1 or 2 in which the preconcentration unit (P) separates the first flow (1) and optionally the second fluid depleted in CO2 (121) by adsorption, for example by pressure shift, or by permeation.

4. Method according to one of the preceding claims in which the first flow (1) contains less than 50% mol CO2 on a dry basis, preferably less than 35% or even less than 30% mol CO2 on a dry basis.

5. Method according to one of the preceding claims in which the CO2-enriched gas (11) contains more than 50 mol% CO2 on a dry basis, preferably more than 90% mol CO2 dry basis.

6. Method according to one of the preceding claims in which the second flow (2) contains at least 50 mol% CO2 on a dry basis, preferably more than 70 mol% CO2 on a dry basis.

7. The method of claim 6 wherein the difference between the first percentage and the second percentage of CO2 on a dry basis is at least 20%, or even at least 40%.

8. Method according to one of the preceding claims in which the second flow (2) is dried, at atmospheric pressure, compressed and then separated in the second separation unit (2F).

9. Method according to one of the preceding claims in which the second CO2-depleted fluid (121) is sent at least partly upstream of the pre-concentration unit (P) possibly by mixing it directly with the first flow (10) and the CO2-enriched gas (11) contains less of the lighter constituent than a residual gas (12) from the pre-concentration unit.

10. Method according to one of the preceding claims in which the second CO2-depleted fluid (121) is mixed under pressure at least in part with the CO2-enriched gas (11) coming from the preconcentration unit (P) after at least one compression step (1E) of the CO2-enriched gas.

11. A method according to any preceding claim wherein the first CO2-depleted fluid (15, 17) is mixed with the second CO2-depleted fluid (121B, 121C).

12. A method according to claim 11 wherein a gas mixture formed by mixing the first and second CO2-depleted fluids (15, 17, 121B) is expanded in a turbine (T).

13. A method according to claim 11 or 12 wherein a gas mixture formed by mixing the first and second CO2-depleted fluids (15, 17, 121B) serves as a regeneration gas in the preconcentration unit (P) which operates by adsorption.

14. Method according to one of the preceding claims in which a fluid (19) containing at least 95 mol% CO2 coming from the first separation unit (1F) is sent to separate in the second separation unit (2F, 2G).

15. Integrated separation apparatus (A,B) comprising a first compressor IC), optionally a first drying unit (1D), a pre-concentration unit (P), for example by adsorption in a adsorption unit, a first separation unit (1F), means for sending a first flow containing a first percentage of CO2 as well as oxygen and possibly water to the compressor to be compressed, possibly means for sending the first compressed flow to be dried in the first drying unit, means for sending the first compressed and possibly dried flow to separate in the preconcentration unit, producing a gas enriched in CO2 and depleted in oxygen compared to the first flow, means for sending the CO2-enriched gas (13) to be separated by partial condensation and / or by distillation in the first separation unit producing a fluid containing at least 95 mol% CO2 (19) and at least a first fluid depleted in CO2 (15, 17), a second compressor (2C), a second drying unit (2D), a second separation unit (2F, 2G) by partial condensation and / or distillation and / or by solidification,means for sending a second flow (2) containing a second percentage of CO2 greater than the first percentage as well as oxygen and water to the second compressor to be compressed, means for sending the second compressed flow (102) to be dried in the second drying unit, means for sending the second compressed and dried flow (104) to be separated by partial condensation and / or by distillation and / or by solidification in the second separation unit, the second separation unit producing a CO2-enriched fluid (119) containing at least 90 mol% of CO2 and depleted in oxygen as well as a second CO2-depleted and oxygen-enriched fluid (121, 121 A, 121B, 121C) and means for sending the second fluid depleted in CO2 at least in part, a. upstream of the pre-concentration unit and / or b. downstream of the pre-concentration unit. to recover the CO2 present in the second CO2-depleted fluid.