Method and apparatus for cryogenic separation of CO2-containing gas to produce CO2-rich fluid

Abstract

The present invention relates to a method for the cryogenic separation of a feed gas (1) containing CO2, at least one component lighter than CO2, and at least one component heavier than CO2, in which the feed gas is compressed (Cl, C2, C3, C4), the compressed gas is cooled in a first heat exchanger (E), and the gas cooled in the first heat exchanger is separated at a low temperature in a first distillation column (C) to produce a CO2-rich fluid, a liquid (8) that is rich in CO2 and depleted in at least one component lighter than CO2, and a gas (7) that is depleted in CO2 and enriched in at least one component lighter than CO2. ), the CO2-depleted gas is heated in a first heat exchanger, a first portion of the CO2-rich liquid (15) is expanded and sent in liquid form to a second distillation column (N), a second portion of the CO2-rich liquid (9) is vaporized in the first heat exchanger and then sent in gaseous form to the tank of the second distillation column, a CO2-depleted liquid (25) and rich in at least one heavier component is withdrawn from the second column, and a CO2-rich gas (21) and depleted in at least one heavier component is withdrawn at the top of the second column as product.

Description

[Technical field]

[0001] The present invention is 2 The gas containing CO is separated at low temperatures. 2 The present invention relates to a process and apparatus for producing a CO rich fluid. 2 And NO 2 etc., CO 2 At least one heavier component, such as carbon monoxide, hydrogen, nitrogen, oxygen, NO, or methane, CO 2 and at least one lighter component.

[0002] In particular, the process treats gases originating from combustion, e.g., oxyfuel combustion processes, boilers, SMRs, to remove, e.g., at least 80 mol % CO 2 , in practice further comprising at least 90 mol % CO 2 Contains CO 2 A product rich in [Background technology]

[0003] CO 2 Gas containing, for example, H 2 PSA or CO 2 It is waste gas from PSA.

[0004] Cryogenic separation operates at temperatures below 0°C, and indeed even below -40°C.

[0005] “A Study of the Extraction of CO 2 from the Flue Gas of a 500 MW Pulverized Coal Fired Boiler”, Energy Conversion and Management, Vol. 33, No. 5-8, 1992, CO 2 The flue gas containing 2 A liquid rich in CO and depleted in lighter components. 2It is known that the process produces a gas that is depleted in heavy components and enriched in lighter components. The gas from the first distillation column is separated in a second distillation column to produce a liquid that is enriched in heavy components and a product of the process, CO. 2 The resulting mixture forms a gas rich in Summary of the Invention [Means for solving the problem]

[0006] The present invention is 2 a first portion of the CO-rich liquid being expanded and sent in liquid form to the second distillation column, and also 2 A second portion of the fatty acid-rich liquid is vaporized in the first heat exchanger and then sent in gaseous form to the bottom of the second distillation column at an arrival point, and the first portion of the liquid is sent to the second column at a level above the arrival point of the second portion of the liquid.

[0007] This vaporization of the liquid contributes to the heat balance of the process and enables operation of the second column as a strip column, with the first portion of the liquid acting as a wash gas.

[0008] According to the present invention, CO 2 and CO 2 At least one lighter component and CO 2 and at least one heavier component, 2 1. A process for producing a CO-rich fluid, comprising: a feed gas being compressed in a compressor including at least two stages; the compressed gas being cooled in a first heat exchanger; and the gas cooled in the first heat exchanger being separated at a low temperature by distillation in at least a first distillation column to produce a CO-rich fluid. 2 is abundant and CO 2 A liquid deficient in at least one lighter component and CO 2 is deficient and CO 2 Generate gas rich in at least one lighter component and CO 2 The depleted gas is heated in the first heat exchanger and 2A liquid depleted in CO and enriched in at least one heavier component is withdrawn from the second column, and 2 and depleted in at least one heavier component is withdrawn at the top of the second column as product. 2 The first portion of the CO-rich liquid is expanded and sent in liquid form to a second distillation column, 2 The process is characterized in that a second portion of the liquid rich in is vaporized in a first heat exchanger and then sent in gaseous form to the bottom of a second distillation column at an arrival point, and the first portion of the liquid is sent to the second column at a level above the arrival point of the second portion of the liquid.

[0009] Other optional features include: CO 2 a third portion of the liquid rich in and depleted in at least one lighter component is vaporized in the first heat exchanger and returned to the first distillation column; CO 2 a portion of the gas rich in and depleted in at least one heavier component is condensed at the top of the second column and returned; CO 2 At least a portion of the cold for condensing a portion of the gas that is rich in and depleted in at least one heavier component is generated by a first closed refrigeration cycle; the compressor of the first refrigeration cycle is driven by a turbine which expands at least a portion of the gas depleted in at least one light component, which is produced by separation of the feed gas by partial condensation and / or distillation; CO 2 the second and optionally third portions of the liquid rich in and depleted in at least one lighter component are pressurized with a pump upstream of the first heat exchanger; The closed refrigeration cycle generates cold energy to cool the first heat exchanger, The compressed and cooled feed gas is 2is separated by partial condensation to produce lean gas and also liquid, and the liquid is separated by distillation in a first distillation column and sent to the top of the first distillation column; The second distillation column operates at a higher pressure than the first distillation column; · The second distillation column operates at the same pressure as the first distillation column.

[0010] According to another aspect of the present invention, CO 2 and CO 2 At least one lighter component and CO 2 and at least one heavier component, 2 1. An apparatus for producing a CO-rich fluid, the apparatus comprising: a compressor including at least two stages; a first heat exchanger; a first distillation column; a second distillation column; a conduit for transmitting a feed gas compressed in the compressor including at least two stages; a conduit for transmitting a compressed gas cooled in the first heat exchanger; 2 is abundant and CO 2 Fluids depleted of lighter components and CO 2 is deficient and CO 2 means for passing a gas cooled in the first heat exchanger, which is separated at a low temperature by distillation in at least a first distillation column to produce a gas enriched in lighter components and a gas enriched in lighter components, 2 a conduit for delivering the depleted gas, an expansion means, and a CO 2 a conduit for delivering a first portion of the CO-rich liquid; 2 means for withdrawing from the second column a liquid depleted in CO and enriched in at least one heavier component; 2 and means for withdrawing at the top of the second column as product a gas rich in at least one heavier component, the gas being vaporized in the first heat exchanger, said means comprising a conduit for sending the expanded first portion in liquid form to a second distillation column; 2and a conduit for delivering the vaporized second portion of the enriched liquid to the bottom of a second distillation column at an arrival point, wherein the first portion of the liquid is delivered to the second column at a level above the arrival point of the second portion of the liquid.

[0011] According to another aspect of the present invention, CO 2 and CO 2 At least one lighter component and CO 2 and at least one heavier component, 2 1. An apparatus for producing a CO-rich fluid, the apparatus comprising: a compressor including at least two stages; a first heat exchanger; a first distillation column; a second distillation column; a conduit for transmitting a feed gas compressed in the compressor including at least two stages; a conduit for transmitting a compressed gas cooled in the first heat exchanger; 2 is abundant and CO 2 A liquid deficient in at least one lighter component and CO 2 is deficient and CO 2 means for passing the gas cooled in the first heat exchanger, which is separated at a low temperature by distillation in at least a first distillation column to produce a gas enriched in at least one lighter component; and a gas enriched in at least one lighter component, which is heated in the first heat exchanger. 2 a conduit for delivering the depleted gas, an expansion means, and a CO 2 a conduit for delivering the expanded first portion in liquid form to a second distillation column; 2 means for withdrawing from the second column a liquid depleted in CO and enriched in at least one heavier component; 2 and means for withdrawing as product at the top of the second column a gas rich in at least one heavier component and depleted in at least one heavier component; and a closed refrigeration cycle including at least one cycle compressor and including at least one product compressor, wherein at least one of the cycle compressors and at least one of the product compressors are incorporated in a single compressor.

[0012] Other optional features allow the device to: Upstream of the first heat exchanger, CO 2 a pump for pressurizing a second portion of the enriched liquid; Upstream of the second distillation column, 2 a pump for pressurizing a first portion of the enriched liquid; Upstream of the first heat exchanger, CO 2 a pump for pressurizing a portion of the rich liquid and an expansion means for expanding said portion of the liquid upstream of the first distillation column; a phase separator for separating the feed gas cooled in the first heat exchanger and means for sending liquid from the phase separator to the first distillation column; a means for delivering liquid from the phase separator to the first distillation column is connected to the top of the first distillation column; Upstream of the first heat exchanger, CO 2 a second portion of the CO-rich liquid and a second distillation column upstream of the CO 2 a single pump for pressurizing a first portion of the enriched liquid; Upstream of the first heat exchanger upstream of the first column, 2 A portion of the CO-rich liquid and a portion of the CO 2 a second portion of the CO-rich liquid and / or a second distillation column upstream of the CO 2 A single pump for pressurizing the first portion of the rich liquid Includes.

[0013] The invention will now be explained in more detail with reference to the figures. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 represents diagrammatically the steps preceding the process according to the invention. [Diagram 2] FIG. 2 illustrates a schematic representation of the process according to the invention. [Diagram 3] FIG. 3 illustrates a schematic representation of the process according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] For example, the process of treating gas resulting from combustion is Gas cooling, Compression of cooling gas, Drying of compressed gases, Separation of compressed gases by pressure swing adsorption (denoted by the familiar acronym PSA), Compression of waste gases produced by PSA, Low pressure separation of compressed waste gas using cryogenic means Includes.

[0016] FIG. 1 shows the first step of a process according to an alternative form of the invention.

[0017] Gas FG (flue gas) is CO 2 and nitrogen-containing combustion gas. It is cooled in a quench tower Q, and water 41 is sent to the top of the tower to reduce the temperature of the gas FG from 160° C. to about 40° C. A portion of the condensate taken off at the bottom of tower Q is cooled against water CW and recycled as stream 45 for cooling the gas FG.

[0018] The cooled gas 43 withdrawn at the top of column Q is saturated with water and compressed by multi-stage compressors C1, C8, C9, C10 to a pressure of about 9 bar absolute. Most of the water in the gas 43 is therefore condensed and the condensate formed in the interstage separators S1, S2, S3 is collected to form part of stream 45.

[0019] The compressed gas is then dried by partial condensation after cooling with water CW and water W originating from a cooling tower T to cool the compressed gas to about 10° C. The water condensed in separator S4 joins stream 45.

[0020] The gas is then converted into CO in this example. 2 The mixture is further dried in a dryer D before being sent to a PSA, denoted PSA, which is a CO 2a nitrogen-rich and nitrogen-depleted gas and a second pressure higher than the first pressure; 2 It produces a gas that is deficient in nitrogen but rich in nitrogen. Regeneration of the PSA is achieved by gas 3, which will be described later.

[0021] The nitrogen-rich gas is expanded from about 8 bar to atmospheric pressure to generate some of the energy to compress the gas FG. It is then mixed with water H in tower T before being sent to air as top gas from tower T. 2 The cooled water W is pumped by pump P2 to cool the gas upstream of separator S4, as already described.

[0022] CO 2 CO resulting from separation by adsorption in the PSA unit 2 The isocyanate-rich gas 1 is compressed in a compressor to about 39 bar and separated at low temperature, i.e. below 0°C, in practice even below -30°C.

[0023] Two different ways of performing these next steps are illustrated in FIGS.

[0024] FIG. 2 illustrates a schematic representation of the process according to the invention.

[0025] Gas stream 1 is compressed in a multi-stage compressor, in this example with four stages C1, C2, C3, C4, with coolers R1, R2, R3 between each pair of stages and two coolers R4, R5 downstream of the last stage. 2 or CO 2 It may be a waste product from the PSA and may be compressed to at least 35 bar absolute in compressor stages C1-C4. Coolers R1-R3 are cooled solely by cooling water CW, as is cooler R5.

[0026] Gas Stream 1 is CO 2and at least one lighter component which may be hydrogen, carbon monoxide, nitrogen or oxygen. In this example, the gas stream is rich in nitrogen. Preferably, gas stream 1 contains less than 1 mol % methane.

[0027] The gas stream cooled in the two coolers R4, R5 downstream of the last stage is cooled in a first heat exchanger E to a temperature below −50° C. by heat exchange with at least one fluid originating from the cryogenic separation. This exchanger E can be a plate-and-fin type exchanger made from brazed aluminium.

[0028] The gas stream 1 is partially condensed in the first heat exchanger E and the two-phase stream formed is separated in a phase separator S to form at least one lighter component, in this example at least nitrogen-rich gas 3. This gas is heated in the first exchanger E and is then the only cooling fluid sent to the first cooler R4, which is heated in this first cooler R4 immediately after the last stage C4 of the compressor, from a temperature of 30° C. to a temperature of 100° C. The gas cooled in the first cooler R4 is then cooled in a second cooler R5 against cooling water CW to an ambient temperature below 40° C., in practice even below 30° C.

[0029] Alternatively, the at least one light component-rich gas stream 3 can cool the compressed gas in a second cooler R5, the first cooler being water cooled.

[0030] Alternatively or additionally, at least one light component-rich stream may cool the compressed gas in a cooler R1, R2, R3 between two stages of the compressor.

[0031] Thus, the gas 3 expanded in the turbine T is preheated against the compressed gas in the compressors C1-C4, thereby enabling the heat of compression to generate more energy in the turbines.

[0032] The light-rich gas stream 3, heated in the first cooler R4, is at 8 bar and is expanded in a turbine T from this pressure to approximately atmospheric pressure. The light-rich gas stream 3 can then be used to regenerate an adsorbent for drying the gas that feeds the PSA producing stream 1. Additionally or alternatively, the expanded stream 3 is cooled to room temperature to remove CO2 that it contains. 2 The resulting mixture can be fed to a PSA unit for recovery.

[0033] The liquid 5 from the phase separator S is sent to the top of the distillation column C, from which CO 2 A liquid 9 rich in and depleted in at least one light component is withdrawn at the bottom. At least a part of the liquid can be pressurized with a pump P and sent to be vaporized in a first heat exchanger E, a part 11 of the liquid vaporized on reboiling is optionally sent to the bottom of the column C, and another part 19 is sent to feed the column N at the bottom. The overhead gas 7 from the column C is heated in the first exchanger E.

[0034] Pump P may simply serve to overcome the hydrostatic pressure and head losses, so that columns C, N operate at the same pressure.

[0035] Alternatively, column C may be operated at a higher pressure than column N, with pressurization of the fluids pumped into the columns allowing for particularly inexpensive operation.

[0036] Tower N is CO 2 A tower for removing the heavier NOx compounds, which are the following compounds: nitric oxide (NO), nitrogen dioxide (NO 2 ), nitrous oxide (N 2 O), dinitrogen tetroxide (N 2 O 4 ) and dinitrogen trioxide (N 2 O 3 ) is the name applied to CO 2 Because it is lighter, tower N is more effective at reducing nitrogen dioxide (NO 2 ), nitrous oxide (N 2 O), dinitrogen tetroxide (N 2 O 4 ) and dinitrogen trioxide (N2 O 3 ) is used to remove

[0037] In this column, fed by stream 19, CO 2 At least one of the heavier impurities is CO 2 15 intermediate reflux and pure CO 2 and NOX compounds, e.g., NO 2 At the bottom, a liquid 25 enriched in at least one heavier impurity such as

[0038] The liquid 25 rich in at least one heavier impurity is vaporized in a first exchanger E.

[0039] The overhead gas 21 from column N constitutes the product purified of at least one heavier impurity and is heated in a first exchanger E before being compressed in a first compression stage C5 driven by a turbine T. After cooling in R6, the stream is split, a portion 23 is condensed in the first exchanger E and the remaining portion 27 is compressed in compression stages C6, C7 to form a compressed gas product. The gas compressed in C7 is the CO2 product of this example. 2 The resulting gas product is rich in

[0040] Portion 23 is returned at the top of column N as reflux.

[0041] Exchanger E, phase separator S and column C are located within an insulating chamber CB.

[0042] Two means of low temperature generation are used. CO 2 is compressed in cycle compressor CC and returned through two different valves to the first heat exchanger where it is cooled, liquefied, separated and expanded forming two streams of 5.5 and 9.5 bar absolute. These two streams are heated in the first heat exchanger E to provide cold and then returned to cycle compressor CC. Vaporization of liquid 9 in exchanger E.

[0043] Obviously, the system may comprise several phase separators in series and / or parallel and upstream of the distillation, and may also comprise at least one distillation column.

[0044] If the system does not include a column separator, the turbine expanded gas is removed at the top of the distillation column.

[0045] Preferably, at least one of the cycle compressors CC and at least one of the product compressors C6, C7 are combined into a single compressor.

[0046] FIG. 3 illustrates, in schematic form, another process according to the invention.

[0047] Gas stream 1 is compressed in a multi-stage compressor, in this example with four stages C1, C2, C3, C4, with coolers R1, R2, R3 between each pair of stages and a single cooler R5 downstream of the final stage C4. 2 It is the waste product from the PSA and may be compressed to at least 35 bar absolute in compressor stages C1-C4. The coolers R1-R3 are cooled solely by cooling water CW, as is the cooler R5.

[0048] Gas Stream 1 is CO 2 and at least one lighter component which may be hydrogen, carbon monoxide, nitrogen or oxygen. In this example, the gas stream is rich in nitrogen. Preferably, gas stream 1 contains less than 1 mol % methane.

[0049] The gas stream cooled in the cooler R5 downstream of the last stage is cooled in a first heat exchanger E to a temperature below −50° C. by heat exchange with at least one fluid originating from the cryogenic separation. This exchanger E can be a plate-and-fin type exchanger made from brazed aluminum.

[0050] Gas stream 1 is partially condensed in a first heat exchanger E and the two-phase stream formed is separated in a phase separator S to form at least one lighter component, a gas 3, which in this example is at least rich in nitrogen. This gas is heated in the first exchanger E and then expanded in a turbine T. Gas 3 contains most of the nitrogen present in stream 1 and also carbon dioxide.

[0051] The light-rich gas stream 3, heated in the first cooler R4, is at 8 bar and is expanded in a turbine T from this pressure to approximately atmospheric pressure. The light-rich gas stream 3 is then heated in an exchanger E and can be used to regenerate the adsorbent for drying the gas that feeds the PSA producing stream 1. The gas used for the regeneration of the dryer D is mixed with the gas separated downstream of the stage C10. In this way, the CO 2 is recovered and more NOX is absorbed during partial condensation upstream of separator S4.

[0052] Additionally or alternatively, the expanded stream 3 may be 2 The resulting mixture can be fed to a PSA unit for recovery.

[0053] The liquid 5 from the phase separator S is expanded to about 14 bar and sent to the top of the distillation column C, from which CO 2 A liquid 9 rich in and depleted in at least one light component is withdrawn at the bottom. The liquid can be pressurized with a pump P or otherwise transferred by pressure difference. A part of the liquid is sent for vaporization in a first heat exchanger E, a part 11 of the liquid vaporized on reboiling is sent to the bottom of column C, and another part 19 is sent in gaseous form to feed column N at the bottom. The remaining part of the pressurized liquid is sent in liquid form as intermediate reflux to column N.

[0054] The top gas 7 from column C is heated in a first exchanger E and enriched with the light components of the liquid 5, such as oxygen, and / or nitrogen, and / or methane, and / or NO. It can be recycled upstream of the PSA.

[0055] Tower N is CO 2 A tower for removing the heavier NOx compounds, which are the following compounds: nitric oxide (NO), nitrogen dioxide (NO 2 ), nitrous oxide (N 2 O), dinitrogen tetroxide (N 2 O 4 ) and dinitrogen trioxide (N 2 O 3 ) is the name applied to CO 2 Because it is lighter, tower N is more effective at reducing nitrogen dioxide (NO 2 ), nitrous oxide (N 2 O), dinitrogen tetroxide (N 2 O 4 ) and dinitrogen trioxide (N 2 O 3 ) is used to remove

[0056] In this tower, which is fed by the CO 2 At least one of the heavier impurities is CO 2 intermediate reflux and pure CO 2 and NOx compounds, e.g. NO 2 At the bottom, a liquid rich in at least one heavier impurity such as

[0057] NO 2 etc., CO 2 A liquid 25 rich in heavier NOx is withdrawn at the bottom of column N. The liquid 25 is heated in exchanger E and then recycled to the combustion gas FG upstream of column Q.

[0058] Compressor C5 driven by turbine T produces CO 2 or forms part of an ammonia refrigeration cycle. The gas is then compressed by other compression stages C6, C7, with water coolers CW between each pair of stages (R6 between C5 and C6) and a final cooler downstream of stage C7.

[0059] The overhead gas 21 from column N is the CO 2 The gas product is rich in CO. 2This gas, rich in and depleted in at least one heavy component, is condensed in heat exchanger 22 and cooled by a refrigeration cycle C22, C23. A portion 28 is returned to column N as reflux, while the remaining portion 24 of the liquid constitutes the product of the process.

[0060] Exchanger E, phase separator S and columns C and N are located within an insulating chamber CB.

[0061] Three means of low temperature generation are used. CO 2 is compressed in cycle compressor CC and returned through two different valves to the first heat exchanger where it is cooled, liquefied, separated and expanded forming two streams of 5.5 and 9.5 bar absolute. These two streams are heated in the first heat exchanger E to provide cold and then returned to cycle compressor CC. Vaporization of liquid 9 in exchanger E. Uses compressors C22 and C23, CO 2 Or the closed ammonia cycle.

[0062] Obviously, the system may comprise several phase separators in series and / or parallel and upstream of the distillation, and may also comprise at least one distillation column.

Claims

1. CO ２ And, ２ At least one lighter component and CO ２ and at least one heavier component, ２ A process for producing a fluid rich in CO, wherein the feed gas is compressed in a compressor (C1, C2, C3, C4) comprising at least two stages, the compressed gas is cooled in a first heat exchanger (E), and the gas cooled in the first heat exchanger is separated at low temperature by distillation in at least a first distillation column (C) to produce a CO ２ is rich in CO ２ a liquid (8) depleted of said at least one lighter component; and CO ２ is deficient and CO ２ and a gas (7) enriched in said at least one lighter component, ２ The depleted gas (7) is heated in the first heat exchanger and ２ A liquid (25) depleted in and enriched in the at least one heavier component is withdrawn from the second column, and ２ and the gas (21) rich in and depleted in said at least one heavier component is withdrawn at the top of said second column as product (24, 27). ２ The first portion (10, 15) of the CO-rich liquid is expanded and sent in liquid form to the second distillation column (N), ２ a second portion (9) of the liquid rich in is vaporized in said first heat exchanger and then sent in gaseous form to the bottom of said second distillation column at an arrival point, said first portion of said liquid being sent to said second column at a level above said arrival point of said second portion of said liquid.

2. CO ２ 2. The process of claim 1, wherein a third portion (17) of the liquid, rich in and depleted in the at least one lighter component, is vaporized in the first heat exchanger (E) and returned to the first distillation column (C).

3. CO ２ 3. The process according to claim 1 or 2, wherein a portion (23, 28) of the gas rich in and depleted in the at least one heavier component is condensed at the top of the second column (N) and returned.

4. CO ２ 4. The process according to claim 3, wherein at least a portion of the cold for condensing said portion (28) of said gas rich in and depleted in said at least one heavier component is produced by a first closed refrigeration cycle (C21, C22, C23).

5. 5. The process according to claim 4, wherein the compressor of the first refrigeration cycle (C21) is driven by a turbine (T) which expands at least a portion (3) of the gas depleted in at least one light component produced by the separation of the feed gas by partial condensation (S) and / or distillation (C).

6. CO ２ 6. The process according to any one of claims 1 to 5, wherein the second part (9) and optionally the third part (17) of the liquid rich in and depleted in the at least one lighter component are pressurized by a pump (P) upstream of the first heat exchanger (E).

7. The process according to any one of claims 1 to 6, wherein a closed refrigeration cycle (C21, C22, C23) produces cold for cooling the first heat exchanger (E).

8. The compressed and cooled feed gas (1) is ２ is separated by partial condensation (S) to produce a lean gas (3) and also a liquid (5), and said liquid is separated by distillation in the first distillation column (C) and sent to the top of said first distillation column.

9. CO ２ And, ２ At least one lighter component and CO ２ and at least one heavier component to separate the feed gas at a low temperature to obtain CO ２ An apparatus for producing a fluid rich in CO, comprising a compressor (C1, C2, C3, C4) including at least two stages, a first heat exchanger (E), a first distillation column (C), a second distillation column (N), a conduit for sending the feed gas compressed in the compressor including at least two stages, a conduit for sending the compressed gas cooled in the first heat exchanger, and ２ is rich in CO ２ a liquid depleted of said at least one lighter component; and CO ２ is deficient and CO ２ a means for passing said gas cooled in said first heat exchanger, which is separated at a low temperature by distillation in at least said first distillation column to produce a gas enriched in said at least one lighter component; and a means for passing said gas cooled in said first heat exchanger, which is heated in said first heat exchanger. ２ a conduit for delivering the depleted gas; an expansion means; ２ means for withdrawing from said second column a liquid (25) depleted in CO and enriched in said at least one heavier component; ２ and means for withdrawing at the top of the second column a gas (21) rich in and depleted in said at least one heavier component as product (24, 27). ２ a conduit for sending a first portion (10, 15) of the expanded liquid to the second distillation column in liquid form; ２ and a conduit for sending the vaporized second portion (9) of the liquid enriched in nitric acid, and a conduit for sending the vaporized second portion at an arrival point to the bottom of the second distillation column, wherein the first portion of the liquid is sent to the second column at a level above the arrival point of the second portion of the liquid.

10. 10. The apparatus according to claim 9, comprising a closed refrigeration cycle including at least one cycle compressor (CC) and including at least one product compressor (C6, C7), wherein at least one cycle compressor and at least one product compressor are combined in a single compressor.

11. The CO ２ 11. Apparatus according to claim 9 or 10, comprising a pump (P) for pressurizing said second portion (9) of enriched liquid.

12. The CO ２ The apparatus according to any one of claims 9 to 11, comprising a pump (P) for pressurizing said first portion (19) of rich liquid.

13. The CO ２ 13. An apparatus according to any one of claims 9 to 12, comprising a pump (P) for pressurising a portion (17) of the rich liquid, and expansion means (17) for expanding said portion of said liquid upstream of said first distillation column (C).

14. 14. An apparatus according to any one of claims 9 to 13, comprising a phase separator (S) for separating the feed gas cooled in the first heat exchanger (E) and means for sending liquid (5) from the phase separator to the first distillation column (C).

15. 15. The apparatus according to claim 14, wherein the means for sending liquid (5) from the phase separator to the first distillation column (C) is connected to the top of the first distillation column.

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