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

Abstract

Title of the invention: Method and apparatus for separating a mixture containing CO2 by partial condensation and / or distillation. In a process for separating a gaseous mixture containing CO2, nitrogen, and oxygen, the compressed, cooled, and dried gaseous mixture (11) is separated by partial condensation and / or distillation (CC), forming a CO2-rich fluid (21) and / or a CO2-rich gas. During a first mode of operation, a stream that is part of the compressed, cooled, and dried flow (23) is sent to a buffer tank (B) and stored. During a second mode of operation, a gaseous flow (31) stored in the buffer tank (B) is sent upstream of the washing unit. Abstract figure: Fig. 2

Description

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

[0001] The present invention relates to a method and apparatus for separating a mixture containing CO2 by partial condensation and / or distillation.

[0002] The mixture contains CO2, nitrogen, oxygen, possibly argon, possibly water.

[0003] The process produces a CO2-rich gas, containing at least 80 mol% CO2, or even at least 95 mol% CO2 and / or a CO2-rich liquid, containing at least 80 mol% CO2, or even at least 95 mol% CO2.

[0004] Certain CO2 capture processes, in particular cryogenic processes, should preferably operate continuously and if possible with limited fluctuations in flow rates and molar mass.

[0005] In order to homogenize the compositions and average the gas flow rates feeding such units, the usual solution is to set up a gasometer: the gases (with variable flow rate and composition) are stored for a certain time (called "residence time") in an enclosure, such as a gasometer, which can be of variable volume or pressure, to possibly ensure a more homogeneous mixture, generally at low pressure (i.e., close to atmospheric pressure) and an averaged flow rate feeding the CO2 capture unit which is continuously withdrawn. It will be ensured that the different gases feeding the gasometer will be suitably mixed by the positioning and orientation of judicious gas inlets / outlets or recirculations or specific designs of injection rods.

[0006] Parallel Flow Regenerative Kilns (PFRK) cement plants operate according to a cyclic process using pairs of kilns, one kiln being in lime production mode, the second being in regeneration mode, fumes of different compositions and flow rates being emitted during a cycle and the CO2 having to be captured from the fumes generated by the process:

[0007] [TAB.l] Nominal operation Smoke flow rate Nm3 / h 33,000 Operating temperature / max °C 120°C Pressure bara atm Composition during Nominal co2 mol% 22.9 h2o mol% 6.5 02 mol% 8.4 n2 mol% 61.3 Ar mol% 0.7 Production time minutes 13 Inversion time minutes 1

[0008] If the CO2 from the fumes is not captured during the inversion time (i.e. the fumes do not feed the CC unit for 1 minute every 14 minutes), a first calculation defines that a “useful” or “displaced” storage volume at Patm of approximately 500 m3 for the nominal case above is necessary (gasometer). The absence of fumes may possibly last less than a minute, for example of the order of ten seconds, but nevertheless disrupts the operation of the partial condensation and / or CC distillation separation unit.

[0009] [Fig.l] illustrates a CO2 purification process using a preconcentration unit A capable of separating a gas by adsorption or permeation and a partial condensation and / or distillation process CC. A gas 1 at atmospheric pressure and a temperature of 120°C containing CO2, nitrogen, oxygen, argon as well as impurities such as NOX and / or SOX is compressed in a compressor C1 forming a compressed gas 3, washed with water 4 and / or a basic component in a washing unit Q to remove impurities such as NOX and SOX.The washed gas 5 is heated in a heater H and sent to a compressor C2 where it is compressed forming a compressed gas 8, cooled in a cooler R forming a cooled gas 9, dried in a dryer D for example by temperature swing adsorption and sent as dried gas 11 to a preconcentration unit, for example separation unit A by pressure swing adsorption producing a nitrogen-enriched and CO2-depleted gas 13 and a CO2-enriched and nitrogen-depleted gas 15. The gas 13 is compressed in a compressor C3 forming a gas 17, is cooled and then separated by partial condensation and / or distillation forming a CO2-rich liquid, containing at least 80 mol% of CO2.

[0010] Gas 1 comes from a flue gas source that does not operate permanently. To supply separation units A, CC during periods when gas is not available, a portion 6 of the gas heated in heater H is sent to a gasometer G while gas 1 is available and stored. While gas 1, 6 is not available, it is gasometer G which sends gas to compressor C2.

[0011] A similar method is known from WO2006 / 106253 and EP-A-341879.

[0012] According to an object of the invention, there is provided a method for separating a gas mixture containing CO2, nitrogen and oxygen in which:

[0013] i. The mixture is purified by washing with water in a washing unit producing a purified flow containing water,

[0014] ii. The purified flow is compressed in a compressor to form a compressed flow and then cooled and dried forming a compressed flow, cooled and dried

[0015] iii. At least a portion of the compressed, cooled and dried flow is separated by partial condensation and / or distillation forming a CO2-rich liquid and / or a CO2-rich gas.

[0016] wherein during a first mode of operation the gas mixture has a flow rate D and a molar mass of CO2 of C and a flow which is a part a. Of the compressed flow rate and / or b. Of the compressed, cooled and dried flow rate and / or c. Of the CO2-rich gas and / or d. Of the CO2-enriched gas and / or e. CO2-rich liquid from partial condensation and / or distillation that has been vaporized

[0017] is sent to a buffer capacity and stored and

[0018] in which during a second mode of operation, the gas mixture has a flow rate less than D, or even zero, and / or a molar mass of CO2 less than C and a gas flow stored in the buffer capacity is sent upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation and / or distillation unit.

[0019] According to another object of the invention, there is provided a method for separating a gas mixture containing CO2, nitrogen and oxygen in which:

[0020] i. The mixture is purified by washing with water in a washing unit producing a purified flow containing water,

[0021] ii. The purified flow is compressed in a compressor to form a compressed flow and then cooled and dried forming a compressed flow, cooled and dried

[0022] iii. At least a portion of the compressed, cooled and dried flow is separated by adsorption or permeation in a preconcentration unit forming a nitrogen-enriched and CO2-depleted gas and a CO2-enriched and nitrogen-depleted gas,

[0023] iv. The CO2-enriched gas is optionally compressed, optionally cooled and then separated by partial condensation and / or distillation in a partial condensation and / or distillation unit forming a CO2-rich liquid and / or a gas rich in CO2 in which during a first mode of operation the gas mixture has a flow rate D and a molar mass in CO2 of C and a flow which is a part a. Of the compressed flow and / or b. Compressed, cooled and dried flow and / or c. CO2-enriched gas and / or d. CO2-rich gas and / or e. CO2-rich liquid from partial condensation and / or distillation that has been vaporized

[0024] is sent to a buffer capacity and stored and

[0025] in which during a second mode of operation, the gas mixture has a flow rate less than D, or even zero, and / or a molar mass of CO2 less than C and a gas flow stored in the buffer capacity is sent upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation and / or distillation unit and downstream of the preconcentration unit.

[0026] According to other optional aspects: • the buffer capacity stores the gas during the first operating mode at a pressure greater than 6 bars abs, or at least equal to 8 bars abs and preferably less than 30 bars abs. • during the second mode of operation, the gas flow stored in the buffer capacity is expanded before being sent upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation and / or distillation unit and possibly downstream of the preconcentration unit. • during the first mode of operation, the flow intended for the buffer capacity is heated upstream of the buffer capacity. • the buffer capacity stores the gas at a temperature above 80°C. • the temperature in the buffer capacity is regulated during the second mode of operation to maintain the temperature above a threshold. • during the first mode of operation a flow which is a part of the compressed, cooled and dried flow is sent to the buffer capacity and stored. • during the first mode of operation, no gas leaves the buffer capacity to be separated in the preconcentration unit, if present, or the partial condensation and / or distillation unit. • during the second mode of operation, no gas is sent to the buffer capacity. • during the second mode of operation, the buffer capacity depressurizes, preferably to atmospheric pressure. • during the first mode of operation, the buffer capacity stores gas at the inlet pressure of the preconcentration unit. • during the first mode of operation, the buffer capacity stores gas at the inlet pressure of the separation unit by partial condensation and / or distillation. • during a second operating mode, the gas mixture has a flow rate lower than D, or even zero and / or a molar mass in CO2 lower than T, a gas flow stored in the buffer capacity is sent upstream of the washing unit. • during a second operating mode, the gas mixture has a flow rate lower than D, or even zero and / or a molar mass in CO2 lower than T, a gas flow stored in the buffer capacity is sent upstream of the compressor of the purified flow. • during a second mode of operation, the gas mixture has a flow rate lower than D, or even zero, and / or a molar mass of CO2 lower than T and a gas flow stored in the buffer capacity is sent upstream of the partial condensation and / or distillation unit and downstream of the dryer. • during a second mode of operation, the gas mixture has a flow rate lower than D, or even zero, and / or a molar mass of CO2 lower than T, and a gas flow stored in the buffer capacity is sent upstream of the partial condensation and / or distillation unit and downstream of the preconcentration unit. • the preconcentration unit operates by pressure swing adsorption • the preconcentration unit operates by permeation using at least one membrane permeation stage operating at room temperature or below 0°C. • a gas delivery from a source richer in CO2 than the gas stored in the buffer capacity is triggered if the CO2 content in the buffer capacity falls below a threshold. • CO2-enriched gas and / or CO2-rich gas and / or CO2-rich liquid from partial condensation and / or distillation that has been vaporized are sent to the buffer tank if, preferably, only if the CO2 content in the buffer tank falls below a threshold.

[0027] According to another object of the invention, there is provided an apparatus for separating a gas mixture containing CO2, nitrogen and oxygen comprising a washing unit, a compressor, a unit for separation by partial condensation and / or distillation, a buffer capacity, means for sending the mixture to be purified by washing with water in the washing unit producing a purified flow containing water, means for sending the purified flow to be compressed in the compressor to form a compressed flow, means for cooling the compressed flow, means for drying the compressed and cooled flow, means for sending at least a portion of the compressed, cooled and dried flow to be separated by partial condensation and / or distillation in the separation unit forming a CO2-rich liquid and / or a CO2-rich gas, means for sending a stream which is a portion a. of the compressed flow and / or b. Compressed, cooled and dried flow and / or c. CO2-rich gas and / or d. CO2-rich liquid from partial condensation and / or distillation that has been vaporized at the buffer capacity

[0028] to be stored and means

[0029] to send a gas flow stored in the buffer capacity upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation and / or distillation unit.

[0030] According to another object of the invention, there is provided an apparatus for separating a gas mixture containing CO2, nitrogen and oxygen comprising a washing unit, a compressor, a preconcentration unit, a unit for separation by partial condensation and / or distillation, a buffer capacity, means for sending the mixture to be purified by washing with water in the washing unit producing a purified flow containing water, means for sending the purified flow to be compressed in the compressor to form a compressed flow, means for cooling the compressed flow, means for drying the compressed and cooled flow, means for sending at least a portion of the compressed, cooled and dried flow to be separated in the preconcentration unit forming a nitrogen-enriched and CO2-depleted gas and a CO2-enriched and nitrogen-depleted gas, means for sending the CO2-enriched gas, possibly compressed,optionally cooled to be separated by partial condensation and / or distillation in the partial condensation and / or distillation separation unit forming a CO2-rich liquid and / or a CO2-rich gas, means for sending a stream which is a part a. of the compressed flow and / or b. of the compressed, cooled and dried flow and / or c. of the CO2-enriched gas and / or d. of the CO2-rich gas and / or e. of the CO2-rich liquid from the partial condensation and / or distillation which has been vaporized,

[0031] to the buffer capacity to be stored and means for sending

[0032] a gas flow stored in the buffer capacity upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation unit and / or distillation and downstream of the preconcentration unit.

[0033] Preferably the apparatus comprises a flow meter for measuring the flow rate of the gas mixture 1, 5, 7 at at least one point of the process.

[0034] Preferably the apparatus comprises an analyzer for detecting the molar mass in CO2 of the flow rate of the gas mixture 1, 5, 7 at at least one point of the process.

[0035] Preferably, the apparatus comprises a regulating unit capable of sending the flow

[0036] to the buffer capacity as a function of the flow rate and / or the molar mass of the gas mixture.

[0037] Preferably, the apparatus comprises a regulating unit capable of sending a gas from

[0038] the buffer capacity upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation and / or distillation unit and downstream of the preconcentration unit.

[0039] depending on the flow rate and / or the molar mass of the gas mixture.

[0040] The apparatus may comprise an analyzer of the gas in the buffer capacity and means for triggering a delivery of gas from a source richer in CO2 than the gas stored in the buffer capacity if the CO2 content in the buffer capacity falls below a threshold.

[0041] The proposed innovation consists of dispensing with the low pressure gasometer G of [Fig.l] by setting up a buffer capacity at a pressure P2 higher than the atmospheric pressure PI supplied by at least one feed gas available at said pressure P2 and by supplying the partial condensation and / or distillation separation unit CC by depressurizing the buffer capacity at the most opportune moment.

[0042] Tl = CT filling time

[0043] T2 = duration of availability of at least one charge gas with CAR2 characteristics (flow rate D2, composition C2, etc.) and at pressure P2 of the buffer capacity CT

[0044] T3 = duration of non-availability of the charge gas with the CAR2 characteristics (i.e. say presenting CAR3 characteristics (i.e. flow rate D3, composition C3, etc.) different from CAR2)

[0045] The buffer capacity will be supplied by a percentage of the feed gas flow rate with characteristics CAR2 for a duration T1 less than or equal to T2. The remaining percentage of feed gas may supply the partial condensation and / or distillation separation unit CC. The buffer capacity will be depressurized to supply the partial condensation and / or distillation separation unit CC for a time at least equal to T3.

[0046] Several decarbonizing gases can be involved in the filling and emptying of the buffer capacity.

[0047] When depressurizing the gas stored in the buffer capacity, the temperatures gas and buffer capacity will decrease. As a result, the risk of water and CO2 freezing must be avoided.

[0048] The invention will be described in more detail with reference to the figures where:

[0049] [Fig.2] represents a method according to the invention.

[0050] [Fig.3] represents a method according to the invention.

[0051] [Fig.4] represents a method according to the invention.

[0052] [Fig.2] represents a method according to the invention in which the gas 1 is constituted by fumes, which are not always available or are not always available with the same flow rate and / or the same molar mass in CO2. For example, the fumes may come from a cement plant where no fumes are available during the inversion of the kilns, i.e. for about one minute.

[0053] Gas 1 can come from at least two different sources, possibly having different flow rates and / or molar masses of CO2.

[0054] Note the absence of gasometer G upstream of compressor C2.

[0055] Gas 1 at atmospheric pressure and a temperature of 120°C containing between 20 and 25 mol% CO2, nitrogen, oxygen as well as impurities such as NOX and / or SOX is compressed to approximately 8 bars in a compressor C1 forming a compressed gas 3, washed with water 4 and / or a basic component in a washing unit Q to remove impurities such as NOX and SOX.The washed gas 5 is heated in a heater H and sent to a compressor C2 where it is compressed forming a compressed gas 8 at a pressure greater than 6 bar abs, cooled in a cooler R forming a cooled gas 9, dried in a dryer D for example by temperature swing adsorption and sent as dried gas 11 according to this first variant to an optional preconcentration unit A which carries out a separation for example by pressure swing adsorption or by permeation producing a nitrogen-enriched and CO2-depleted gas 13 and a CO2-enriched and nitrogen-depleted gas 15. The CO2-enriched gas 15 is compressed in a compressor C3 forming a gas 17, is cooled and then separated by partial condensation and / or distillation forming a CO2-rich gas, containing at least 80 mol% of CO2 and / or a CO2-rich liquid, containing at least 80 mol% of CO2.

[0056] During a first mode of operation, the gas 1 is available with a flow rate D and a CO2 concentration in mol% C. The method produces a CO2-rich gas, containing at least 80 mol% of CO2, or even at least 95 mol% of CO2 and / or a CO2-rich liquid 21, containing at least 80 mol% of CO2, or even at least 95 mol% of CO2. During this first mode, a buffer capacity B is filled by taking a portion 23, 26, 29 of the gas 1, 5 downstream of the compressor C2 and / or a portion 21, 27 of a gas enriched in CO2 relative to the gases 1, 5, for example the gas 25 and / or the gas 27.

[0057] Several locations are possible to divert this gas to the buffer capacity B according to the invention: • At the outlet of the intermediate compression stages C2 of gas 5 upstream of drying and cooler R (flow 26) or after compression in C3 of gas 15 (flow 27). • At the outlet of the intermediate stage coolers or the final cooler R of compressor C2 (flow 29). • Downstream of dryers D to provide dry compressed gas (stream 23, this variant being the most preferable).

[0058] The use of gases 25, 27 will be described later.

[0059] It is also possible to divert the gas to the buffer capacity B from a point downstream of the preconcentration unit, taking for example the gas 27 enriched in CO2 before or after compression in the compressor C3.

[0060] It is also possible to divert the gas to the buffer capacity B by taking a gas and / or vaporizing a liquid 21 enriched in CO2 or rich in CO2 in the partial condensation and / or distillation unit.

[0061] The gas supplying the buffer capacity can come from several different points.

[0062] The buffer capacity B will be pressurized for Tl=13 minutes by a flow rate constituting 1 / 13 of the flow rate of the charge gas 1 during the first mode of operation then depressurized during the second mode of operation for T3=1 minute (for example, during the inversion time of the kilns, if the gas 1 comes from a cement plant) in order to maintain a substantially constant feed flow rate to the partial condensation and / or distillation separation unit CC.

[0063] The volume of the buffer capacity B required at 20°C, 8 bar is 60 m3 (much lower than the volume of gasometer G of 500 m3, Patm of [Fig.l]).

[0064] In this example of [Fig.2], the gas is stored in the buffer capacity B at the inlet pressure of the preconcentration unit A, for example a PSA adsorption separation unit A (between 60 and 30 bar abs, 8 bar abs for example) or a permeation separation unit, the permeation using for example at least one membrane permeation step operating at ambient temperature or below 0°C.

[0065] During the second mode of operation, gas 1 is not available and gas 31 released from buffer capacity B supplies compressor C1 with fumes 31 which replace gas 1 in order to maintain continuous operation of the entire compressor C1, washing unit Q and compression in compressor C2.

[0066] The gas constituting the flow 31 can be sent to the washing tower Q as flow 4 and / or upstream of the compressor C2 and downstream of the washing tower Q as flow 32 and / or to an intermediate stage of the compressor C2 as flow 33.

[0067] It should be noted that during the depressurization of the gas stored in the buffer capacity B from 8 bars to a lower pressure, for example Patm, the temperatures of the gas 31 and the buffer capacity B will decrease (approximately 1.2°C / sec), i.e. a temperature drop of approximately 70°C at the inlet of the compressor Cl. Consequently, to avoid the risks of freezing of the water and CO2, it will be preferable to store a dry gas 23 taken downstream of the dryer D, preferably preheated in a dedicated heater H.

[0068] It is thus possible to design a preheating temperature of the stored gas of 100°C (i.e. a storage capacity which increases from 60 m3 to 100 m3) at the start of depressurization, making it possible to reach 20°C at the end of depressurization in order to limit the temperature variations at the inlet of compressor C1.

[0069] As the buffer capacity B is pressurized, the temperature will increase: it will be necessary to regulate the preheating temperature by the heater H of the gas 23 supplying the buffer capacity B to maintain a temperature of 100°C at the bottom of the buffer capacity B by means of a regulation means TIC.

[0070] It will therefore be preferable to store a dry gas (gas 23 from the outlet of dryer D for example) and / or to maintain a sufficiently high temperature in buffer capacity B (via a preheater H for example) to avoid freezing of the water and / or CO2 during the depressurization of buffer capacity B. This will also avoid the risks of formation of acid condensates (in the presence of SOx in the gas in particular). The temperature in buffer capacity B can be controlled by the preheating rate of heater H.

[0071] It will be noted that the preheater H can be used to heat any flow rate 21, 23, 26, 27, 29 and can heat a mixture of at least two of these gases.

[0072] According to a second variant, either the preconcentration unit A or the compressor C are not present, for example in the case of a cement plant operating by oxy-combustion.

[0073] In the absence of the preconcentration unit, the dried gas 11 is sent directly from the dryer D to the partial condensation and / or distillation and / or solidification separation unit CC to be separated.

[0074] In this case, without a preconcentration unit P, the mixture 1 is purified by washing with water in a washing unit Q producing a purified flow 5 containing water, the purified flow is compressed in a compressor C2 to form a compressed flow then, cooled and dried forming a compressed flow, cooled and dried, at least a part 11 of the compressed flow, cooled and dried is separated by partial condensation and / or distillation CC forming a gas enriched in nitrogen and depleted in CO2 and a gas enriched in CO2 and depleted in nitrogen in a partial condensation and / or distillation unit forming a liquid rich in CO2 and / or a gas rich in CO2.

[0075] During a first mode of operation the gas mixture has a flow rate D and a molar mass in CO2 of C and a flow which is a part of the compressed flow rate 1 and / or the flow rate compressed, cooled and dried 11 and / or CO2-rich gas and / or CO2-enriched gas and / or CO2-rich liquid from partial condensation and / or distillation which has been vaporized is sent to a buffer capacity B and stored.

[0076] During a second mode of operation, the gas mixture 1 has a flow rate lower than D, or even zero, and / or a molar mass of CO2 lower than C and a gas flow stored in the buffer capacity B is sent upstream of the washing unit Q or upstream of the compressor C1 of the purified flow or upstream of the partial condensation and / or distillation unit.

[0077] In the case (with or without preconcentration) where a gas flow 1 is always available during the second mode of operation but with fluctuating characteristics (for example flow rate and / or composition) and assuming that the compressor C1 and the washing unit Q can manage the fluctuations (or an intermittent operating situation if the flue gas flow 1 is available punctually for a certain time), it will be possible to depressurize the buffer capacity B and send gas that it stores to the inlet of the flue gas compressor C1 (preferably) as in [Fig. 2] or upstream of the compressor C2 or to an inter-stage of the compressor C2, as illustrated in [Fig. 3], for the flow 33.

[0078] [Fig.3] shows a variant of [Fig.2] in which the gas 31 from the buffer capacity B is expanded to the outlet pressure of the compressor C1 and is sent to the washing tower Q as flow 4 or upstream of the compressor C2 as flow 32.

[0079] In this case, the expansion of the flow 31 will be less and less heating will be required from the preheater H to compensate for the cold generated by the expansion.

[0080] [Fig. 3] shows that the sending of the CO2-enriched and / or CO2-rich flows 21, 27 is regulated by a CO2 concentration analyzer CONC which detects the CO2 concentration of the gas in the buffer capacity. In this way it is possible to compensate for a drop in the CO2 concentration of the gas 1. It is possible to use the gases 21, 27 to supply the buffer capacity only in the case where the CO2 concentration of the gas in the buffer capacity drops.

[0081] The apparatus also comprises a TIC apparatus for measuring the temperature of the gas in the buffer capacity and for regulating the operation of the preheater H to maintain the temperature in the buffer capacity B at a given value.

[0082] For the second variant where the preconcentration unit A and the compressor C3 are absent, a CO2-enriched gas and / or a CO2-enriched vaporized liquid can be sent to the buffer capacity B to increase its molar mass in CO2.

[0083] [Fig.4] shows a method according to the invention according to the first variant with preconcentration A and compressor C3, in which the buffer capacity B is supplied with gas 23 taken downstream of the dryer D, as for figures 2 and 3.

[0084] To smooth out composition fluctuations towards the separation unit by partial condensation and / or distillation CC, it will also be possible to pressurize the buffer capacity B with additional gases, richer in CO2 than gases 1, 5, 23, 26, 29, such as the residual 27 from the adsorption unit A or the liquid rich in CO2 21 produced by the unit CC and vaporized in a vaporizer V. Thus, as seen in Figures 2, 3 and 4, a flow 25 from the vaporizer V brings a gas rich in CO2 to the buffer capacity B. The sending of this gas to the buffer capacity B is triggered according to the CO2 concentration of the gas in the buffer capacity B measured by the analyzer CONC by opening a valve to let the flow 25 pass. If the molar mass of CO2 falls below the value C of the molar mass of CO2 of gas 1 during the first mode, the sending of gas 25 and / or 27 is triggered to enrich the stored gas in CO2.

[0085] It is also possible to consider depressurizing the buffer capacity B at the inlet of the partial condensation and / or distillation separation unit CC to limit the fluctuations that it may have to manage. Thus the flow 34 is sent from the capacity B to the inlet of the compressor C3 to supply the unit CC.

[0086] For the management of fluctuations at the inlet of the adsorption unit A, during the second mode of operation, it is possible to envisage recycling all or part 33 of the CO2-enriched gas 15 to the adsorption unit A to increase its inlet flow rate and its molar mass in CO2.

[0087] For all of Figures 2 to 4, buffer capacity B is not supplied with gas during the second mode of operation and no gas leaves buffer capacity B to be sent for separation in units A or CC during the first mode of operation.

[0088] The buffer capacity does not store liquid.

[0089] In the case of [Fig.4], it is noted that the preheater is not present to heat the gas 23 intended for the buffer capacity. As the buffer capacity in this case provides gas 34 at relatively high pressure after expansion in the valve, less cold is generated and the preheater H is not essential. On the other hand, it can nevertheless be present to heat the flow 23 or another gas supplying the buffer capacity, for example the flow 27 coming from the compressor C3 and / or the vaporizer V of liquid rich in CO2 coming from the separation CC.

[0090] In all the figures, it may be necessary to recycle a portion 33 of the CO2-depleted gas 15 upstream of the preconcentration unit A to separate there and thus compensate for a drop in flow rate in the gas coming from the dryer D.

[0091] The method and apparatus described herein could be applied to the case where the separation of the CC unit is done at least in part by pressure swing adsorption or by permeation.

[0092] The figures do not illustrate a flow meter for measuring the flow rate of the gas mixture 1, 5, 7 at at least one point of the process and an analyzer for detecting the molar mass in C02 of the flow rate of the gas mixture 1, 5, 7 at at least one point of the process.

[0093] The apparatus may comprise a regulating unit capable of sending the flow

[0094] to the buffer capacity as a function of the flow rate and / or the molar mass of the gas mixture.

[0095] The apparatus comprises a regulating unit capable of sending a gas from

[0096] the buffer capacity upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation and / or distillation unit and downstream of the preconcentration unit.

[0097] depending on the flow rate and / or the molar mass of the gas mixture.

[0098] Otherwise the sending of flow and / or gas can be triggered manually.

Claims

Claims

1. A method of separating a gas mixture containing CO2, nitrogen and oxygen in which: i. The mixture (1) is purified by washing with water in a washing unit (Q) producing a purified flow (5) containing water, ii. The purified flow is compressed in a compressor (C2) to form a compressed flow and then cooled and dried (D) forming a compressed, cooled and dried flow (11) iii. At least a portion (17) of the compressed, cooled and dried flow is separated by partial condensation and / or distillation (CC) forming a liquid (21) rich in CO2 and / or a gas rich in CO2 in which during a first mode of operation the gas mixture has a flow rate D and a molar mass in CO2 of C and a flow which is a part a. Compressed flow (26, 29) and / or b. Compressed, cooled and dried flow (23) and / or c. CO2-rich gas and / or d. CO2-rich liquid (21) from partial condensation and / or distillation that has been vaporized is sent to a buffer capacity (B) and stored and in which during a second mode of operation, the gas mixture (1) has a flow rate lower than D, or even zero and / or a molar mass in CO2 lower than C and a gas flow (4, 31, 32, 33, 34) stored in the buffer capacity (B) is sent upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation and / or distillation unit.

2. A method of separating a gas mixture (1) containing CO2, nitrogen and oxygen in which: i. The mixture is purified by washing with water in a washing unit (Q) producing a purified flow (5) containing water, ii. The purified flow is compressed in a compressor (C2) to form a compressed flow and then cooled and dried forming a compressed, cooled and dried flow (11) iii. At least a portion of the compressed, cooled and dried flow is separated by adsorption or permeation in a preconcentration unit (A) forming a nitrogen-enriched and CO2-depleted gas (13) and a CO2-enriched and nitrogen-depleted gas (15), iv. The CO2-enriched gas is optionally compressed, optionally cooled and then separated by partial condensation and / or distillation in a partial condensation and / or distillation unit (CC) forming a CO2-rich liquid (21) and / or a CO2-rich gas in which during a first mode of operation the gas mixture has a flow rate D and a molar mass in CO2 of C and a flow which is a part a. Compressed flow (26, 29) and / or b. Compressed, cooled and dried flow (23) and / or c. CO2-enriched gas (27) and / or d. CO2-rich gas and / or e. CO2-rich liquid (21) from partial condensation and / or distillation that has been vaporized is sent to a buffer capacity (B) and stored and in which during a second mode of operation, the gas mixture has a flow rate lower than D, or even zero and / or a molar mass in CO2 lower than C and a stored gas flow (4, 31, 32, 33, 34) in the buffer capacity is sent upstream of the washing unit or upstream of the compressor of the purified flow or upstream of the partial condensation and / or distillation unit and downstream of the preconcentration unit.

3. Method according to claim 1 or 2 in which the buffer capacity (B) stores the gas (26, 29, 23, 27, 21) during the first mode of operation at a pressure greater than 6 bars abs, or even at least equal to 8 bars abs and preferably less than 30 bars abs.

4. Method according to one of the preceding claims during the second mode of operation, the gas flow (3, 31, 33) stored in the buffer capacity is expanded before being sent upstream of the washing unit (Q) or upstream of the compressor of the purified flow (C2) or upstream of the partial condensation and / or distillation unit (CC) and possibly actually downstream of the preconcentration unit (A).

5. Method according to one of the preceding claims during the first mode of operation, the flow (26, 29, 23, 27, 21) intended for the buffer capacity (B) is heated upstream of the buffer capacity.

6. A method according to claim 4 wherein the buffer capacity (B) stores the gas (26, 29, 23, 27, 21) at a temperature above 80°C.

7. A method according to either of claims 4 or 5 wherein the temperature in the buffer capacity (B) is regulated during the second mode of operation to maintain the temperature above a threshold.

8. Method according to one of the preceding claims in which during the first mode of operation a flow (23) which is a part of the compressed, cooled and dried flow is sent to the buffer capacity (B) and stored.

9. Method according to one of the preceding claims in which during the first mode of operation, no gas leaves the buffer capacity (B) to be separated in the preconcentration unit (A), if present, or the partial condensation and / or distillation unit (CC).

10. Method according to one of the preceding claims in which during the second mode of operation, no gas is sent to the buffer capacity (B).

11. Method according to one of the preceding claims in which during the second mode of operation, the buffer capacity (B) depressurizes, preferably to atmospheric pressure.

12. A method according to claim 2 or one of the preceding claims when dependent on claim 2 wherein during the first mode of operation, the buffer capacity (B) stores gas at the inlet pressure of the preconcentration unit (A).

13. Method according to one of the preceding claims in which during the first mode of operation, the buffer capacity (B) stores gas at the inlet pressure of the partial condensation and / or distillation separation unit (CC).

14. Method according to one of the preceding claims in which during a second mode of operation, the gas mixture has a flow rate less than D, or even zero and / or a molar mass of CO2 less than T, a gas flow stored in the buffer capacity (B) is sent upstream of the washing unit (Q).

15. A method according to any preceding claim wherein during a second mode of operation, the gas mixture has a flow rate less than D, or even zero and / or a molar mass of CO2 lower than T, a gas flow (32) stored in the buffer capacity is sent upstream of the compressor of the purified flow (C2).

16. Method according to one of the preceding claims in which during a second mode of operation, the gas mixture (1) has a flow rate less than D, or even zero and / or a molar mass of CO2 less than T and a gas flow (34) stored in the buffer capacity is sent upstream of the partial condensation and / or distillation unit (CC) and downstream of the dryer (D).

17. Method according to claims 2 and 16 in which during a second mode of operation, the gas mixture has a flow rate less than D, or even zero and / or a molar mass of CO2 less than T, and a gas flow (34) stored in the buffer capacity (B) is sent upstream of the partial condensation and / or distillation unit (CC) and downstream of the preconcentration unit (A).

18. A method according to claim 2 or one of claims 3 to 17 when dependent on claim 2 wherein the preconcentration unit (A) operates by pressure swing adsorption or by permeation using at least one membrane permeation step operating at room temperature or below 0°C.

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