Method and device for separating a mixture containing co2 via partial condensation and / or distillation

Abstract

The invention relates to a method for separating a gaseous mixture containing CO2, nitrogen and oxygen, wherein the compressed, cooled and dried gaseous mixture (11) is separated via partial condensation and / or distillation (CC) to form a CO2-rich fluid (21) and / or a CO2-rich gas, and wherein, in a first operating mode, a stream which is part of the compressed, cooled and dried stream (23) is sent to a buffer capacity (B) and stored and, in a second operating mode, a gaseous stream (31) stored in the buffer capacity (B) is sent upstream of the washing unit.

Description

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] Some CO2 capture processes, particularly 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(i.e., close to atmospheric pressure) and an averaged flow rate feeding the CO2 capture unit which is continuously withdrawn.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 are properly mixed by the positioning and orientation of judicious gas inlets / outlets or recirculations or specific designs of injection pipes.

[0006] Parallel Flow Regenerative Kilns (PFRK) cement plants operate using a cyclic process using pairs of kilns, with one kiln in lime production mode and the other in regeneration mode. Flue gases of different compositions and flow rates are emitted during a cycle, and CO2 must be captured from the flue gases generated by the process:

[0007] [TAB.1]Nominal operationSmoke flow rateNm 3 / h33,000Operating temperature / max℃120°CPressurebaraatmCompositionpendantNominalCO2mol%22.9H2Omol%6.5O2mol%8.4N2mol%61.3Armol%0.7Production timeminutes13Inversion timeminutes1

[0008] If the CO2 from the fumes is not captured during the inversion time (i.e. the fumes do not supply the CC unit for 1 minute every 14 minutes), a first calculation defines that a “useful” or “displaced” storage volume at P atm of about 500 m 3for the nominal case above is necessary (gasometer). The absence of fumes can possibly last less than a minute, for example of the order of ten seconds but nevertheless disrupts the operation of the partial condensation separation unit and / or CC distillation.

[0009] illustrates a CO2 purification process using a preconcentration unit A capable of separating a gas by adsorption or permeation and a process by partial condensation and / or distillation CC. A gas 1 at atmospheric pressure and a temperature of 120°C containing CO2, nitrogen, oxygen, argon as well as impurities such as NO x and / or the SO x 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 NO x and the SO x. 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 gas 13 enriched in nitrogen and depleted in CO2 and a gas 15 enriched in CO2 and depleted in nitrogen. 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 liquid rich in CO2, containing at least 80 mol% of CO2.

[0010] Gas 1 comes from a flue gas source that is not operating continuously. 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, gasometer G 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 in CO2 of C and a flow which is a part of the compressed, cooled and dried flow and possibly of the compressed flow taken upstream of the cooling and / or the drying and / or of the CO2-rich gas and / or of the CO2-enriched gas and / or of the CO2-rich liquid from the partial condensation and / or the distillation which 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, CO2-depleted gas and a CO2-enriched, 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 CO2-rich gas in which during a first mode of operation the gas mixture has a flow rate d and a molar mass of CO2 of C and a stream which is a part of the compressed, cooled and dried flow and optionally of the compressed flow taken upstream of the cooling and / or drying and / or

[0024] and / orCO2-enriched gas and / orCO2-rich gas and / orCO2-rich liquid from partial condensation and / or distillation that has been vaporized

[0025] is sent to a buffer capacity and stored and

[0026] 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.

[0027] According to other optional aspects: the buffer capacity stores the gas during the first mode of operation at a pressure greater than 6 bar abs, or even at least equal to 8 bar abs and preferably less than 30 bar 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 reheated upstream of the buffer capacity. the buffer capacity stores the gas at a temperature greater than 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 stream which is a part of the compressed, cooled and dried flow is sent to the buffer tank and stored.during the first mode of operation, no gas leaves the buffer tank 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 tank.during the second mode of operation, the buffer tank depressurizes, preferably to atmospheric pressure.during the first mode of operation, the buffer tank stores gas at the inlet pressure of the preconcentration unit.during the first mode of operation, the buffer tank stores gas at the inlet pressure of the partial condensation and / or distillation separation unit.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 is sent upstream of the washing unit.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 is sent upstream of the compressor of the purified flow.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 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 adsorptionthe preconcentration unit operates by permeation using at least one membrane permeation stage operating at ambient temperature or below 0°C.a sending of gas 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 is sent to the buffer capacity if, preferably, only if the CO2 content in the buffer capacity falls below a threshold.

[0028] 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 flow which is a portion of the compressed flow and / or of the compressed flow,cooled and dried and / orCO2-rich gas and / orCO2-rich liquid from partial condensation and / or distillation that has been vaporized at the buffer capacity,

[0029] to be stored and means

[0030] 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.

[0031] 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 of the compressed flow and / or of the compressed, cooled and dried flow and / or of the CO2-enriched gas and / or of the CO2-rich gas and / or of the CO2-rich liquid from the partial condensation and / or distillation which has been vaporized,

[0032] to the buffer capacity to be stored and means to send

[0033] 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 and downstream of the preconcentration unit.

[0034] 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.

[0035] 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.

[0036] Preferably, the apparatus comprises a regulating unit capable of sending the flow

[0037] to the buffer capacity depending on the flow rate and / or the molar mass of the gas mixture.

[0038] Preferably, the apparatus comprises a regulating unit capable of sending a gas from

[0039] 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.

[0040] depending on the flow rate and / or the molar mass of the gas mixture.

[0041] 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.

[0042] The proposed innovation consists of doing away with the low pressure gasometer G by setting up a buffer capacity at a pressure P2 higher than the atmospheric pressure P1 supplied by at least one feed gas available at said pressure P2 and by supplying the separation unit by partial condensation and / or distillation CC by depressurizing the buffer capacity at the most opportune moment.

[0043] T1 = CT filling time

[0044] T2 = duration of availability of at least one charge gas with the characteristics CAR2 (flow rate d2, composition C2, etc.) and at the pressure P2 of the buffer capacity CT

[0045] T3 = duration of unavailability of the feed gas with CAR2 characteristics (i.e. presenting CAR3 characteristics (i.e. flow rate d3, composition C3, etc.) different from CAR2)

[0046] The buffer capacity will be supplied by a percentage of the feed gas flow rate with CAR2 characteristics 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.

[0047] Several decarbonizing gases can be involved in filling and emptying the buffer capacity.

[0048] When the gas stored in the buffer tank is depressurized, the temperatures of the gas and the buffer tank will decrease. Consequently, the risk of water and CO2 freezing must be avoided.

[0049] The invention will be described in more detail with reference to the figures where:

[0050] represents a method according to the invention.

[0051] represents a method according to the invention.

[0052] represents a method according to the invention.

[0053] represents a method according to the invention in which the gas 1 consists of 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 approximately one minute.

[0054] Gas 1 can come from at least two different sources, possibly having different flow rates and / or molar masses of CO2.

[0055] Note the absence of gasometer G upstream of compressor C2.

[0056] 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 NO x and / or the SO x is compressed to about 8 bar 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 NO x and the SO x. 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.

[0057] 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% CO2, or even at least 95 mol% CO2 and / or a CO2-rich liquid 21, containing at least 80 mol% CO2, or even at least 95 mol% CO2. During this first mode, a buffer capacity B is filled by taking a portion 23 of the gas 1, 5 downstream of the compressor C2, taken for example downstream of the dryers D. This gas 23 can be mixed with a portion 26, 29 of the gas 1, 5 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.

[0058] Several optional locations are possible to divert the gas to be mixed with the gas 23 sent to the buffer capacity B according to the invention: At the outlet of the intermediate compression stages C2 of the gas 5 upstream of the drying and the cooler R (flow 26) or after compression in C3 of the gas 15 (flow 27). At the outlet of the intermediate stage coolers or the final cooler R of the compressor C2 (flow 29).

[0059] The use of gases 25, 27 will be described later.

[0060] It is also possible to derive gas to be mixed with gas 23 and sent to buffer capacity B from a point downstream of the preconcentration unit, taking for example gas 27 enriched in CO2 before or after compression in compressor C3.

[0061] It is also possible to derive gas to be mixed with gas 23 and sent to 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.

[0062] The gas supplying the buffer capacity can come from several different points.

[0063] The buffer capacity B will be pressurized for T1=13 minutes by a flow rate constituting 1 / 13 of the flow rate of the feed gas 1 during the first mode of operation and 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 rate to the partial condensation separation and / or distillation unit CC.

[0064] The volume of buffer capacity B required at 20°C, 8 bar is 60 m 3(much less than the gasometer volume G of 500 m 3 , P atm of the).

[0065] In this example, 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.

[0066] During the second mode of operation, gas 1 is not available or is available with a flow rate lower than d 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.

[0067] 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.

[0068] It should be noted that when depressurizing the gas stored in the buffer capacity B from 8 bar to a lower pressure, e.g. P atm , the temperatures of gas 31 and buffer capacity B will decrease (approximately 1.2°C / sec), i.e. a temperature drop of approximately 70°C at the inlet of compressor C1. Consequently, to avoid the risk of freezing of water and CO2, it will be preferable to store a dry gas 23 taken downstream of dryer D, preferably preheated in a dedicated heater H.

[0069] We can thus design a preheating temperature of the stored gas of 100°C (i.e. a storage capacity which increases from 60 m 3 100 m away 3) at the start of depressurization allowing 20°C to be reached at the end of depressurization in order to limit temperature variations at the inlet of compressor C1.

[0070] 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 TIC regulation means.

[0071] 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 SO xin the gas 1 in particular). The temperature in the buffer capacity B can be controlled by the preheating rate of the heater H.

[0072] It will be noted that preheater H can be used to heat any flow 21, 23, 26, 27, 29 and can heat a mixture of at least two of these gases.

[0073] 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 oxycombustion.

[0074] 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.

[0075] 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.

[0076] 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 1 and / or the compressed, cooled and dried flow 11 and / or the CO2-rich gas and / or the CO2-enriched gas and / or the CO2-rich liquid from the partial condensation and / or the distillation which has been vaporized is sent to a buffer capacity B and stored.

[0077] 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 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.

[0078] 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 compressor C1 and scrubbing unit Q can handle the fluctuations (or an intermittent operating situation if flue gas flow 1 is available punctually for a certain time), buffer capacity B can be depressurized and gas stored therein sent to the inlet of flue gas compressor C1 (preferably) as in or upstream of compressor C2 or to an inter-stage of compressor C2, as illustrated in, for flow 33.

[0079] La shows a variant of the 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.

[0080] In this case, the expansion of flow 31 will be less and less heating will be required from preheater H to compensate for the cold generated by the expansion.

[0081] Lamontre shows that the delivery of 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 gas 1. It is possible to use gases 21, 27 to supply the buffer capacity only in the case where the CO2 concentration of the gas in the buffer capacity drops.

[0082] The device also includes a TIC device 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.

[0083] 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.

[0084] Lamontre shows a process 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.

[0085] To smooth out the composition fluctuations towards the partial condensation and / or distillation separation unit CC, it will also be possible to pressurize the buffer capacity B with additional gases, richer in CO2 than the gases 1, 5, 23, 26, 29, such as the residual 27 from the adsorption unit A or the CO2-rich liquid21 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 CO2-rich gas towards the buffer capacity B. The sending of this gas towards the buffer capacity B is triggered according to the CO2 concentration of the gas in the buffer capacity B measured by the CONC analyzer 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 for enrich the stored gas with CO2.

[0086] 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, flow 34 is sent from capacity B to the inlet of compressor C3 to supply the CC unit.

[0087] To manage fluctuations at the inlet of adsorption unit A, during the second mode of operation, it is possible to consider recycling all or part 33 of the CO2-enriched gas15 to adsorption unit A to increase its inlet flow rate and its CO2 molar mass.

[0088] For all 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 to separation in units A or CC during the first mode of operation.

[0089] The buffer capacity does not store liquid.

[0090] In the case of the, we note that the preheater is not present to heat the gas 23 intended for the buffer capacity. Since 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.

[0091] In all 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.

[0092] 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.

[0093] 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 CO2 of the flow rate of the gas mixture 1, 5, 7 at at least one point of the process.

[0094] The device may include a regulating unit capable of sending the flow

[0095] to the buffer capacity depending on the flow rate and / or the molar mass of the gas mixture.

[0096] The device includes a regulating unit capable of sending a gas from

[0097] 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

[0098] depending on the flow rate and / or the molar mass of the gas mixture.

[0099] Otherwise the sending of flow and / or gas can be triggered manually.

Claims

A method for separating a gas mixture containing CO2, nitrogen and oxygen in which: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 and then cooled and dried (D) forming a compressed, cooled and dried flow (11)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 CO2in 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 stream which is a portion of the compressed, cooled and dried flow (23) and optionallyOf the compressed flow taken upstream of the cooling and / or drying (26,29) and / orCO2-rich gas and / orCO2-rich liquid (21) from the partial condensation and / or distillation which has been vaporized is sent to a buffer tank (B) and stored and 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 C and a gas flow (4, 31, 32, 33, 34) stored in the buffer tank (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., A method for separating a gas mixture (1) containing CO2, nitrogen and oxygen in which:The mixture 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 and then cooled and dried forming a compressed, cooled and dried flow (11)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), 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 CO2 molar mass of C and a stream which is a part of the compressed, cooled and dried flow (23) and optionally of the compressed flow taken upstream of the cooling and / or drying (26, 29) and / or of the CO2-enriched gas (27) and / or of the CO2-rich gas and / or of the CO2-rich liquid (21) from the partial condensation and / or distillation which 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 less than d, or even zero, and / or a CO2 molar mass less than C and a stored gas flow rate (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., 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. 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 downstream of the preconcentration unit (A). 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. Method according to claim 4 in which the buffer capacity (B) stores the gas (26, 29, 23, 27, 21) at a temperature above 80°C. Method according to one of claims 4 or 5 in which the temperature in the buffer capacity (B) is regulated during the second mode of operation to maintain the temperature above a threshold. 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. 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). 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). Method according to one of the preceding claims, in which during the second mode of operation, the buffer capacity (B) is depressurized, preferably to atmospheric pressure. 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). 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). 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). 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 (32) stored in the buffer capacity is sent upstream of the compressor of the purified flow (C2).

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