Method and apparatus for separating a mixture containing co2

Abstract

The invention relates to a method for separating a gas mixture (1) having a dew point between 0 and 15°C at a first pressure, which gas mixture contains carbon dioxide and at least one first component that is heavier than carbon dioxide, which method comprises the steps of cooling the mixture at the first pressure to a temperature between 0 and 15°C and at least partially condensing the first component of the mixture in a first heat exchanger (E1) in order to obtain a two-phase mixture by indirect heat exchange with a pressurised liquid stream (29) which vaporises in the heat exchanger, separating the liquid phase (H) from the cooled two-phase mixture in order to obtain a liquid phase containing at least one first component and a gas phase (3) depleted of at least one first component, the liquid stream being produced by separating the gas phase.

Description

[0001] Title: Process and apparatus for separating a mixture containing CO2

[0002] The present invention relates to a method and apparatus for separating a mixture containing CO2 and at least one first component heavier than carbon dioxide. The mixture has a dew point temperature between 0 and 15°C at a first pressure.

[0003] CO2 capture using a low-temperature process sometimes involves using a refrigerant to condense at least one component heavier than carbon dioxide, such as water, from the gas to be treated. This step significantly reduces the content of the at least one component heavier than carbon dioxide in the gas before the gas passes through an adsorbent to remove the last traces of condensable molecules.

[0004] Carbon dioxide (CO2) capture by a partial condensation and / or distillation process operating at less than 0°C most often requires drying the wet gas to be treated, rich in CO2, upstream of the low-temperature separation to remove condensable molecules, mainly water (H2O), to avoid any risk of freezing. This drying is often divided into two stages: first, the gas is cooled in one or more heat exchangers to condense a large part of these molecules, then this CO2-rich gas passes through an adsorbent to remove the last traces of condensable molecules.

[0005] It is known to those skilled in the art that the cold required to condense the water from the humid, CO2-rich gas is often produced using a refrigeration unit. A heat transfer fluid (Freon®, ammonia, propane, etc.) is used to transfer this cold to a cold water loop and then to the humid, CO2-rich gas.

[0006] GB-A-2416389 describes a process for cooling wet CO2 in which compressed wet CO2 is cooled first with seawater in a first heat exchanger and then by two flows of gaseous CO2 in a second heat exchanger to condense water contained in the CO2 upstream of an adsorption unit. The water is removed by means of a phase separator downstream of the two exchangers.

[0007] Refrigeration units linked to the cold water loop, such as that of the first exchanger of GB-A-2416389, are expensive and inefficient equipment. The invention proposes an improvement of the CO2 capture process by carrying out thermal integration to cool the wet gas which feeds the CO2 capture process. Thus, the refrigeration unit and its cold water network are no longer necessary or can be reduced in size.

[0008] US2020 / 309451 describes a process in which all the liquid produced by a CO2 separation process is used to condense water in the flow to be separated. The liquid remains in liquid or supercritical form, to be fed into a pipeline. By using only sensible heat to condense the water, it is necessary to send a large quantity of liquid to the heat exchanger, in this case the entire liquid production of the process.

[0009] “Gas conditioning - The interface between CO2 capture and transport” by Aspelund et al, International Journal of Greenhouse Gas Control, 2007, pp343-354 describes a CO2 separation process in which water is condensed by heat exchange with CO2-rich fluids produced by distillation. However, it appears that these fluids are all gaseous.

[0010] In addition, the exchanger for cooling the wet gas carries out an exchange between only two fluids.

[0011] The cold required to condense water or another component having a relatively high condensation temperature is directly withdrawn from the part of the process operating at low temperature via at least a portion of the liquid CO2 produced. The invention applies in the case where the CO2 capture unit produces CO2 in the gaseous or liquid state or dense phase. Indeed, whatever the state of the CO2 produced, the cryogenic separation process necessarily passes through the liquid phase (liquid resulting from the partial condensation and / or from the distillation column and / or from the cycle in the case of liquid production).

[0012] The invention consists, according to one of the variants, of:

[0013] 1) Condensation of water by evaporation of CO2

[0014] • Cool a pressurized humid gas, rich in CO2 and H2O, in a heat exchanger by indirect heat exchange to a temperature between 0 and 15°C and partially condense the water it contains by vaporizing a liquid rich in CO2, for example pressurized liquid CO2.

[0015] • Separate liquid water from cooled pressurized wet gas.

[0016] 2) Conditioning of liquid CO2

[0017] • The cold required to partially condense this humid, CO2-rich gas is provided by a liquid CO2 flow from the part of the process operating at low temperature and vaporizing in the exchanger. This liquid CO2 flow is drawn from part of the liquid from a liquefaction or from part of the liquid production from the distillation column and / or from the partial condensation and / or from the cycle in the case of a separation producing a liquid, pumped (if necessary) to obtain a pressure between 30 and 50 bara and then de-subcooled (if necessary) in the main exchanger of the cryogenic unit in order to obtain a temperature between -5 and 15°C in order to be sent to the heat exchanger. These temperatures and pressures are chosen to avoid any risk of freezing of the water in the exchanger.

[0018] 3) The recovery of the gaseous CO2 obtained

[0019] • The CO2 leaves the heat exchanger with a temperature between 5 and 80°C, preferably between 20 and 40°C, and is returned to a stage of the CO2 compressor or directly into the gaseous CO2 product if the pressure of the gaseous CO2 is lower than the pressure of the CO2 evaporating in the heat exchanger. In this way, energy savings are achieved in compressing the CO2.

[0020] • The de-subcooling of step 2) can be achieved by mixing the pumped liquid CO2 with warmer CO2 in order to obtain the temperature between -5 and 15°C. This avoids a pass through the main exchanger of the cryogenic unit.

[0021] This invention, by using the potentially excess cold from the part operating at low temperature, allows the refrigeration unit and the cold water loop to be removed. This reduces the number of equipment required and therefore the cost, as well as the energy consumption of this CO2 capture process (savings in the energy consumption of the refrigeration unit and the gain in compression of the pumped CO2).

[0022] According to one object of the invention, there is provided a method for separating a gas mixture having a dew point temperature between 0 and 15°C at a first pressure, containing carbon dioxide and at least one first component heavier than carbon dioxide, and optionally at least one second component lighter than carbon dioxide, comprising the following steps: i) Cooling the mixture at the first pressure to a temperature between 0 and 15°C and at least partial condensation of the first component of the mixture in a first heat exchanger in order to obtain a two-phase mixture by indirect heat exchange with a pressurized liquid flow ii) Separation of the liquid phase from the cooled two-phase mixture in order to obtain a liquid phase containing at least one first component and a gas phase depleted in at least one first component iii) Cooling the gas phase or a gas derived from the gas phase in a second heat exchangerheat and iv) Either liquefaction or separation as follows: a) Either liquefaction of the cooled gas phase to produce a CO2-rich liquid b) Or separation by partial condensation and / or distillation of the cooled gas phase or of a gas derived from the cooled gas phase to produce a liquid enriched in CO2 and optionally depleted in the at least one second component relative to the gas mixture and v) The liquid stream of step i) constitutes a part of the CO2-rich or CO2-enriched liquid of step iv)a) or b) or of a liquid derived therefrom characterized in that a pressurized liquid stream which vaporizes in the first heat exchanger.

[0023] The liquid stream preferably contains at least 95 mol% CO2.

[0024] According to other optional aspects of the invention:

[0025] • at least one first component is water, methanol or ammonia.

[0026] • the second component, if present, is nitrogen, oxygen, hydrogen, carbon monoxide or methane.

[0027] • the CO2-enriched liquid is at least part of a bottom liquid of a distillation column.

[0028] • the CO2-enriched liquid is at least part of a liquid from a phase separator

[0029] • the CO2-rich liquid is at least part of a liquid from a phase separator

[0030] • the CO2-enriched liquid is pressurized by a pump to a pumping pressure of between 30 and 50 bara and then heated to a temperature of between -5 and 10°C before being sent to the first heat exchanger. • the CO2-enriched liquid comes from a CO2 cycle, part of the cycle of which operates under a second pressure, preferably greater than 30 bara, or even greater than 46 bara.

[0031] • the CO2-enriched liquid is cooled to a temperature between -5 and 10°C then expanded to a third pressure between 30 and 46 bara and without change of state.

[0032] • another CO2-enriched liquid from liquefaction or partial condensation and / or distillation is vaporized in the second heat exchanger and the CO2-enriched gas obtained at the outlet of the second heat exchanger is sent to a CO2 compressor or directly into the CO2 gas produced.

[0033] • the other liquid is a fraction of the column bottom liquid

[0034] • the CO2-enriched liquid vaporized in the first heat exchanger is sent to the CO2 compressor, possibly at pumping pressure or at the third pressure or directly into the CO2 gas produced or to the distillation column or to a liquid product of the distillation column.

[0035] • the other CO2-enriched liquid is sent to the second heat exchanger at a lower pressure than the CO2-enriched liquid sent to the first heat exchanger.

[0036] • the gas mixture is cooled upstream of the first heat exchanger by heat exchange with water or another refrigerant.

[0037] • the gas derived from the gas phase is formed by separating the gas phase by adsorption, permeation and / or partial condensation and / or distillation.

[0038] • the gas derived from the gas phase is derived therefrom by being separated, for example by adsorption or permeation, to reduce its content of the at least one lighter component

[0039] • the gas derived from the gas phase is derived by compression and drying

[0040] • the first exchanger carries out an indirect heat exchange between only two fluids.

[0041] • CO2-enriched liquid contains at least 95% CO2 and is produced by partially condensing the cooled gas phase.

[0042] • the vaporized CO2-enriched liquid is sent to mix with the gas phase upstream of a partial condensation and / or distillation step. • the liquid which is derived from the CO2-rich liquid or the CO2-enriched liquid is derived from it by purification and / or pumping and / or expansion.

[0043] • the liquid flow vaporizes completely in the first heat exchanger

[0044] • liquid from the column bottom vaporizes in the second exchanger, preferably without having been compressed or expanded, and the vaporized liquid is sent at least in part to the column bottom in gaseous form

[0045] • liquid from the column bottom vaporizes in the second exchanger, preferably without having been compressed or expanded, and the vaporized liquid is sent partly to the column bottom in gaseous form and partly to the product compressor

[0046] • the liquid flow sent to the first heat exchanger constitutes between 5 and 15% of the column tank liquid.

[0047] • the part of the liquid enriched in CO2 is vaporized by indirect heat exchange with the mixture which cools in step i) forming a flow of vaporized liquid and the flow of vaporized liquid is sent at least in part to the bottom of the column in gaseous form to separate there.

[0048] • the depleted mixture, for example dried, is cooled in a second heat exchanger in which the flow of vaporized liquid cools.

[0049] • the CO2-depleted flow is cooled in a second heat exchanger in which the vaporized liquid flow is cooled.

[0050] • the depleted mixture, for example dried, is cooled in a second heat exchanger in which the flow of vaporized liquid does not cool

[0051] • the CO2-depleted flow is cooled in a second heat exchanger in which the vaporized liquid flow is not cooled.

[0052] • the flow of vaporized liquid does not cool before being sent to the bottom of the distillation column and / or mixed with the liquid enriched in CO2 pressurized by a pump

[0053] • the depleted mixture, for example dried, or the flow depleted in CO2 is cooled in a second heat exchanger in which the part of the liquid enriched in CO2 heats up before step v). • another part of the liquid enriched in CO2 heats up and vaporizes in the second heat exchanger and is sent to the bottom of the column in gaseous form to separate there.

[0054] • another part of the CO2-enriched liquid vaporizes in the second heat exchanger and is sent to a customer without having been compressed.

[0055] • a fraction of the CO2-enriched liquid is pressurized by a pump and part of the pressurized liquid constitutes the liquid used to cool the mixture in step i).

[0056] • part of the pressurized liquid is expanded to form a liquid product.

[0057] • at least part of the vaporized flow is sent in gaseous form at a first temperature to mix with part of the pressurized liquid intended to serve as a product which is at a second temperature, lower than the first temperature.

[0058] According to another object of the invention, there is provided an apparatus for separating a gas mixture having a dew point temperature between 0 and 15°C at a first pressure, containing carbon dioxide and at least one first component heavier than carbon dioxide, and optionally at least one second component lighter than carbon dioxide, comprising a first heat exchanger, a second heat exchanger, means for sending the mixture at the first pressure to cool in the first heat exchanger by indirect heat exchange to a temperature between 0 and 15°C in order to obtain a two-phase mixture by indirect heat exchange, means for sending a pressurized liquid stream to the first heat exchanger, means for removing a condensed portion of the first component from the mixture, means for sending a gas phase depleted in at least one first component to the second heat exchanger to cool,means for separating the cooled gas phase in the second heat exchanger comprising a distillation column, means for removing a CO2-rich liquid from the distillation column, means for sending a portion of the CO2-rich liquid to the first heat exchanger, this portion constituting the liquid flow and means for sending at least a portion of the vaporized liquid flow from the first heat exchanger to the tank of the distillation column to separate there or to a product compressor to serve as product or to a liquid flow withdrawn from the distillation column.,

[0059] Preferably, the apparatus comprises means for pressurizing a flow of CO2-rich liquid withdrawn from the bottom of the column to form a pressurized flow and means for sending a portion of the vaporized liquid flow from the first heat exchanger to mix with the pressurized liquid flow.

[0060] Preferably, the means for pressurizing a flow of CO2-rich liquid withdrawn from the bottom of the column to form a pressurized flow are connected to means for dividing the liquid into two downstream of the second heat exchanger forming a first and a second part of the liquid and the apparatus comprises means for sending the first part of the liquid connected to the first heat exchanger and means for sending the second part of the liquid from the second heat exchanger to mix with the bottom liquid.

[0061] The invention will be described in more detail with reference to the figures where: [FIG.1] represents a method according to the invention.

[0062] [FIG.2] represents a method according to the invention.

[0063] [FIG.3] represents a method according to the invention.

[0064] [FIG.4] represents a method according to the invention.

[0065] [FIG.5] represents a part of a method according to the invention.

[0066] [FIG.6] represents a continuation of the method according to the invention of [FIG.5]

[0067] [FIG.7] represents an alternative continuation of the method according to the invention of [FIG.5]

[0068] In [FIG.1 ], a gas mixture 1 at a first pressure contains carbon dioxide, at least one first component, having a condensation temperature between 0 and 15°C at the first pressure, for example water, methanol and ammonia, and at least one second component lighter than carbon dioxide, for example nitrogen, oxygen, hydrogen, methane, carbon monoxide. The gas mixture 1 may also contain a component heavier than carbon dioxide.

[0069] The gas mixture 1 is at a temperature between 5 and 25°C. It is sent to a first heat exchanger E1 where it exchanges heat indirectly with a flow of liquid CO2 29 in order to cool down to a temperature between 0°C and 15°C, the mixture 1 still being at the first pressure.

[0070] At least one first component contained in the gas mixture condenses forming a condensate H, for example condensed water, which is removed in a phase separator S1. The gas 3 enriched in CO2 and depleted in the at least one first component is compressed in a compressor C1 forming a flow 5 which is dried in a dryer D to remove remaining water and then compressed in a compressor C2 to a pressure between 15 and 65 bara. The flow 7 compressed in the compressor C2 is sent to partially condense in a second heat exchanger E2 forming a two-phase flow 9. The flow 9 is separated in the separator S2 into a gas 11 depleted in CO2 and enriched in at least one second component and a liquid 13 depleted in the at least one second component and enriched in CO2.

[0071] Exchangers E2, E3 can constitute a single exchanger.

[0072] Liquid 13 is expanded and sent to the top of a distillation column K.

[0073] The gas 11 is partially condensed in a third heat exchanger E3 forming a two-phase flow which is separated in a phase separator S3 forming a gas 17 depleted in CO2 and enriched in at least one second component and a liquid 15 depleted in the at least one second component and enriched in CO2. The gas 17 is heated in the third and second heat exchangers E3, E2. The liquid 15 is expanded and sent to the top of the column K.

[0074] The overhead gas 21 from column K is heated in the third and second heat exchanger E3, E2 and is sent between the compressors C1, C2 being mixed with flow 5.

[0075] The bottom liquid 19 of column K is withdrawn as flow 19 enriched in CO2 and depleted in at least one second component. The liquid 19 is divided into two parts 23 and 25. The part 23 is expanded in a valve, forming a two-phase flow which is separated in a phase separator S4. The liquid 35 from the separator S4 vaporizes in one of the second and third exchangers and the gas 33 from the separator S4 heats up in the second and third exchangers, the two heated gases thus formed being mixed forming the flow 37 which is compressed in the compressors C3, C4 in series forming a CO2-rich product 41 in gaseous form. The part 25 is separated to form part 29 and the remainder 27 of this part vaporizes in the second heat exchanger E2 before being sent to the bottom of column K providing reboiling in the form of a gaseous flow.

[0076] Part of the flow 27 can be sent to compressor C3.

[0077] Part 29 is pressurized by a pump P up to a pressure between 30 and 50 bars abs then a fraction of the pressurized part 29 heats up or even vaporizes in the exchanger E2 while the rest of the pressurized part 29 does not enter the exchanger E2. The fraction sent to the exchanger E2 and the rest that is not sent there are mixed to obtain liquid CO2 with the desired subcooling. This mixture is sent at a temperature between -5 and 10°C to vaporize in the first heat exchanger E1 by heat exchange only with flow 1

[0078] The temperature between -5 and 10°C can be achieved by mixing pumped liquid CO2 with warmer CO2 (e.g. some CO2 produces 39, 41).

[0079] Part 29 vaporized in the first exchanger E1 and the gas formed is sent at a temperature between 5 and 40°C to a point between compressors C3, C4 by mixing with the flow 39 compressed in compressor C3 whose outlet pressure is between 15 and 46 bars and less than or equal to the pumping pressure of part 29.

[0080] Alternatively, the first exchanger E1 can be located between the compressors C1, C2.

[0081] The gas purified by the condensation of the first component in the exchanger E1 can be dried in an adsorption unit, for example by TSA, downstream of the phase separator S1 and upstream of the compressor C1.

[0082] Alternatively, the liquid CO2 sent to the first heat exchanger E1 may come from a refrigeration cycle in which carbon dioxide circulates. This cycle may provide cold for the partial condensation and / or distillation process. Part of the cycle operates under a second pressure, preferably greater than 30 bara, or even greater than 46 bara. The liquid in the cycle is cooled to a temperature between -5 and 10°C, expanded to a third pressure between 30 and 46 bara and without change of state, then sent to the first heat exchanger E1 as flow 29. Alternatively, gas 3 or a gas resulting therefrom may be separated in a pressure swing adsorption (PSA) unit to generate a low-pressure product compressed in compressor C1 and a high-pressure product.

[0083] Alternatively, the gas 3 is sent to the exchanger E2 without intermediate compression. According to a variant, Figure 1 may comprise an adsorption separation step to reduce the content of the gas phase 3 in at least one lighter component, for example upstream of the compressor C1.

[0084] The liquid stream 29 sent to the first heat exchanger constitutes between 5 and 15% of the tank liquid 19 of column K in Figures 1 to 3.

[0085] Figure 2 illustrates this variant where the gas 3 purified of water and / or methanol and / or ammonia H is separated by adsorption A upstream of the four-stage compressor C1. The adsorption produces a gas 3B enriched in the at least one lighter component and depleted in CO2 and a gas 3A enriched in CO2 and depleted in the at least one lighter component. The gas 3A is then compressed in the compressor C1, dried in the dryer D, for example by TSA, and compressed in the three-stage compressor C2. The number of stages of the compressors C2, C3 is obviously variable.

[0086] Another difference with Figure 1 is that a part 28 of the gas 27 vaporized in the exchanger E2 is sent to the product compressor at a higher pressure than that of the flows 33, 35. Thus the flows 33, 35 are first compressed in a compressor C3 and then are mixed with the flow 28 to be compressed in the compressor C3'. The vaporized liquid 29 mixes with the gas from the compressor C3' and the mixture is compressed in the compressor C4. Figure 3 represents the version of Figure 1 without adsorption unit A but with the compression of a part 28 of the gas 27.

[0087] [FIG.4] represents a method according to the invention in which the liquid providing the necessary cold to the heat exchanger E1 to condense the at least one first component, for example water, is at least a part of the feed flow taken after drying in the exchanger E1 and preferably after drying by adsorption. The liquid 29 is part of the liquid condensed in the phase separator S2, produced by partial condensation of the flow 9 compressed in the compressors C1, C2 and cooled in the exchanger E2. The liquid 29 can otherwise be taken from the separator S3. The liquid 29 is expanded in a valve and then vaporizes in the heat exchanger E1 and is returned in gaseous form between the compressors C1, C2, to compensate for the pressure drop in the pipes and the exchanger E1 by the compression in C2. The rest of the figure is unchanged from [FIG.1].

[0088] Alternatively, a portion of the liquid 15 is used to cool the heat exchanger E1 to condense the at least one first component.

[0089] Liquid 29 preferably contains at least 95 mol% CO2.

[0090] In a variant not illustrated, a gas mixture having a dew point temperature between 0 and 15°C at a first pressure, containing carbon dioxide and at least one first component heavier than carbon dioxide is cooled to a temperature between 0 and 15°C at the first pressure in a first heat exchanger. This causes at least partial condensation of the first component of the mixture in the first heat exchanger to obtain a two-phase mixture by indirect heat exchange with a pressurized liquid stream which vaporizes in the heat exchanger. The liquid phase of the cooled two-phase mixture is separated to obtain a liquid phase containing at least one first component and a gas phase depleted in at least one first component. The gas phase is cooled in a second heat exchanger and liquefied forming a CO2-rich liquid containing at least 95 mol% CO2.A portion of this liquid serves as the liquid stream to condense the at least one first component in the first heat exchanger.

[0091] According to a variant, Figure 4 may comprise an adsorption separation step to reduce the content of the gas phase 3 in at least one lighter component, for example upstream of the compressor C1.

[0092] Figures 5 to 7 illustrate a new way of using vaporized fluid in the case where the refrigerant happens to be high pressure liquid CO2.

[0093] As part of an investment cost optimization, particularly possible on units processing a small quantity of gas, it is possible to consider a scheme possibly without a product compressor. This change requires rethinking the location where the high-pressure CO2 vaporized in the gas condenser was recycled.

[0094] But the method according to figures 5 to 7 also applies to processes with a product compressor. In [FIG. 5], a gas mixture 1 containing carbon dioxide, at least one component heavier than carbon dioxide, for example water and at least one component lighter than carbon dioxide is cooled in a heat exchanger E1 to condense at least a part of the heavier component, for example water and / or methanol and / or ammonia, contained therein and to form a dried mixture. Preferably the heavier component, for example water, is condensed by indirect heat exchange in the heat exchanger E1 with only one flow, a liquid flow 29 enriched in CO2 from the separation of the dried mixture. The liquid flow enriched in CO2 is vaporized as a result.

[0095] Gas 3 is dried in a dryer D and then separated by one of the processes illustrated in [FIG.6] and [FIG.7],

[0096] A first variant of the invention is illustrated in [FIG.6]. It consists of using the vaporized CO2-enriched liquid in its entirety as reboiling gas for a distillation column in the cryogenic section. Very often this dry gas flow rate will not be sufficient to allow efficient reboiling and will therefore only be a supplement to the conventional reboiling source which constitutes a portion of the vaporized liquid CO2 in the main heat exchanger. [FIG.6] shows this new configuration of the section operating at low temperature. This variant therefore makes it possible to efficiently recycle the vaporized CO2, in particular in the case where the process does not include a product compressor. However, this invention can also be applied in the case where such a compressor is present and will thus make it possible to simply reduce the flow rate of the vaporized liquid in the main heat exchanger sent to the column.

[0097] The gas mixture 3, the content of which has been reduced in the at least one heavier component H and possibly in the at least one lighter component (for example by adsorption), is cooled in the second heat exchanger E2 where it partially condenses. The two-phase flow is withdrawn at an intermediate level of the heat exchanger E2 and sent to a phase separator S2. The liquid formed is sent to the top of the column K and the gas formed cools in the second heat exchanger E2 to be partially condensed. The flow formed is separated in a phase separator S3, the gas 17 of which is heated in the heat exchanger E2, the liquid being sent to the top of the column K. The gas 17 can then be separated by permeation, in a known manner.

[0098] The liquid sent to column K is separated to form a gas 21 enriched in the at least one component lighter than CO2 and a liquid enriched in CO2 19. The gas 21 heats up in the heat exchanger E2 and can be mixed with the gas mixture, for example after an adsorption step to increase the CO2 content of the gas mixture. The liquid 19 is divided in two, one part being divided to form a flow 27 which is vaporized in the second heat exchanger E2 and which serves as reboil gas of column K without having been cooled in the heat exchanger E2. Another liquid flow is expanded to form a two-phase flow which is separated in a separator S4. The gas 33 and the liquid 35 formed are heated and vaporized in the case of the liquid and are mixed forming a gas. This gas can serve as a product after or without compression in a compressor.Another portion of the tank liquid 19 is pressurized by a pump, for example to at least 30 bar abs. A portion 29 of the pressurized liquid in the pump P vaporizes in the heat exchanger E2 and serves to cool the first heat exchanger E1, being itself vaporized. The vaporized liquid is mixed with the gas resulting from the vaporization of the liquid 27 downstream of the heat exchanger E2 and the mixture serves as reboiling gas for the column. A portion 51 of the pressurized liquid is reheated in the heat exchanger E2 and is mixed with the pressurized liquid to reheat it forming a liquid 55 as product. The liquid pressurized by the pump which is not sent to the heat exchanger E2 must be expanded slightly to compensate for the pressure losses of the portion 51 which joins it forming the liquid 55.

[0099] A refrigeration cycle using PR propane is used to produce the cold needed for the process which produces a percentage of the CO2 in liquid form.

[0100] A short-circuit circuit 31 makes it possible to vary the temperature of the liquid 29 sent to the first heat exchanger E1.

[0101] A second variant of the invention is illustrated in [FIG.7]. This is a variant of [FIG.6] and only the elements different from those of [FIG.6] are identified in the figure, for clarity. It consists of sending the gaseous CO2 both as reboiling of the distillation column but also as a heat source in order to “de-subcool” the liquid production. Indeed, particularly in the context of high-pressure liquid production (>30 bara), the liquid withdrawn at the bottom of the distillation column and then pumped up to the production pressure is too cold to be stored or transported under the usual conditions (we often speak of 2°C of subcooling compared to the equilibrium temperature). Thanks to this scheme proposed in [Fig.7], it is thus possible to heat the production while greatly reducing energy consumption compared to the scheme of [Fig.6 in the context of high-pressure production.

[0102] A portion of the vaporized liquid in the first heat exchanger E1 is sent to the column K as reboiling gas and another portion of the vaporized liquid 29A is mixed with liquid 55 drawn from the bottom of the column K and pressurized by a pump P to at least 30 bar abs. Thus a portion 29A of the vaporized flow is sent in gaseous form at a first temperature mixing with a portion of the pressurized liquid 55 intended to serve as a product which is at a second temperature, lower than the first temperature. The mixture formed 57 constitutes a de-subcooled liquid at at least 30 bar abs. This characteristic can be exploited in the case where a portion of the vaporized liquid is not sent from the first heat exchanger E1 to the column K.

[0103] Neither the part of the vaporized liquid in the first heat exchanger E1 sent to the column K as reboiling gas nor the other part of the vaporized liquid 29A is mixed with liquid 55 withdrawn from the bottom of the column K is cooled downstream of the first heat exchanger E1.

[0104] It is possible, as described above, to send the dried gas mixture in the dryer directly to the low-temperature separation without separating it between the dryer and the low-temperature separation by pressure swing adsorption. Alternatively, the dried gas mixture in the dryer can be separated directly by pressure swing adsorption between the dryer and the low-temperature separation. The adsorption separation forms a gas enriched in the at least one light component, e.g., hydrogen and / or nitrogen, and a gas depleted in this component. The gas depleted in this component, which is lighter than CO2, is enriched in CO2 and can be compressed in the compressor and separated by partial condensation and distillation.

[0105] In the version of [FIG. 7], the heated liquid 51 does not exist and is not returned to the liquid pumped in pump P. If a valve is shown in this figure, it may exist, for example to equalize the pressures between the liquid pressurized by pump P and the flow 29A.

[0106] In fact, in this specific case, sending all the flow coming from the first heat exchanger E1 to the reboiler of column K would have increased the quantity of CO2 recycled to the compressor and therefore the latter's energy consumption.

[0107] No part of the gas 29A is sent to the heat exchanger 2A either before or after mixing with the pressurized liquid.

Claims

Claims 1. A method for separating a gas mixture (1) having a dew point temperature between 0 and 15°C at a first pressure, containing carbon dioxide and at least one first component heavier than carbon dioxide, and optionally at least one second component lighter than carbon dioxide, comprising the following steps: i) Cooling the mixture at the first pressure to a temperature between 0 and 15°C and at least partial condensation of the first component of the mixture in a first heat exchanger (E1) in order to obtain a two-phase mixture by indirect heat exchange with a pressurized liquid stream (29) ii) Separation of the liquid phase (H) from the cooled two-phase mixture in order to obtain a liquid phase containing at least one first component and a gas phase (3) depleted in at least one first component iii) Cooling the gas phase (3) or a gas (3A,5) derived from the gas phase in a second heat exchanger (E2) and iv) Either liquefaction or separation as follows: a) Either liquefaction of the cooled gas phase to produce a CO2-rich liquid b) Either separation by partial condensation and / or distillation of the cooled gas phase or of the gas derived from the cooled gas phase to produce a CO2-enriched liquid (13, 15, 19, 25, 29) and optionally depleted in the at least one second component relative to the gas mixture and v) The liquid stream of step i) constitutes a portion of the CO2-rich or CO2-enriched liquid of step iv) a) or b) or of a liquid derived therefrom, the liquid stream preferably containing at least 95 mol% CO2 characterized in that the liquid stream vaporizes in the first heat exchanger.

2. The method of claim 1 wherein the at least one first component is water, methanol or ammonia.

3. A method according to claim 1 or 2 wherein the second component, if present, is nitrogen, oxygen, hydrogen, carbon monoxide or methane.

4. Method according to one of the preceding claims in which the CO2-enriched liquid (29) is at least part of a tank liquid (19) of a distillation column (K).

5. Method according to one of the preceding claims in which the CO2-enriched liquid (29) is pressurized by a pump (P) to a pumping pressure of between 30 and 50 bara and then heated to a temperature of between -5 and 10°C before being sent to the first heat exchanger.

6. Method according to one of the preceding claims 1 to 4 in which the CO2-enriched liquid (29) comes from a CO2 cycle of which part of the cycle operates under a second pressure, preferably greater than 30 bara, or even greater than 46 bara.

7. Method according to claim 6 in which the CO2-enriched liquid (29) is cooled to a temperature between -5 and 10°C then expanded to a third pressure between 30 and 46 bara and without change of state.

8. Method according to one of the preceding claims in which another liquid (23) enriched in CO2 originating from the liquefaction or partial condensation and / or the distillation is vaporized in the second heat exchanger (E2) and the gas enriched in CO2 (37) obtained at the outlet of the second heat exchanger is sent to a CO2 compressor (C3, C4) or directly into the gaseous CO2 produced.

9. Method according to one of the preceding claims in which the CO2-enriched liquid (19, 29, 29A) vaporized in the first heat exchanger (E1) is sent to the CO2 compressor (C3, C4), optionally at the pumping pressure or at the third pressure or directly into the gaseous CO2 produced or to the distillation column (K) or to a liquid product (55) of the distillation column.

10. Method according to claim 8 in which the other CO2-enriched liquid (23) is sent to the second heat exchanger (E2) at a pressure lower than that of the CO2-enriched liquid (20) sent to the first heat exchanger (E1).

11. Method according to one of the preceding claims in which the gaseous mixture (1) is cooled upstream of the first heat exchanger (E1) by heat exchange with water or another refrigerant.

12. Method according to one of the preceding claims in which the gas (5) derived from the gas phase (3) is formed by separating the gas phase by adsorption, permeation and / or partial condensation and / or distillation.

13. Method according to one of the preceding claims in which the first exchanger (E1) carries out an indirect heat exchange between only two fluids (1, 29).

14. Method according to one of the preceding claims in which the CO2-enriched liquid (29) contains at least 95% CO2 and is produced by partially condensing (S2, S3) the cooled gas phase (7).

15. Apparatus for separating a gas mixture (1) having a dew point temperature between 0 and 15°C at a first pressure, containing carbon dioxide and at least one first component heavier than carbon dioxide, and optionally at least one second component lighter than carbon dioxide, comprising a first heat exchanger (E1), a second heat exchanger (E2), means for sending the mixture at the first pressure to cool in the first heat exchanger by indirect heat exchange to a temperature between 0 and 15°C in order to obtain a two-phase mixture by indirect heat exchange, means for sending a liquid stream (29) under pressure to the first heat exchanger, means for removing a condensed portion (H) of the first component of the mixture, means for sending a gas phase (3) depleted in at least one first component to the second heat exchanger to cool,means for separating the cooled gas phase in the second heat exchanger comprising a distillation column (K), means for removing a CO2-rich liquid (19) from the distillation column, means for sending a portion of the CO2-rich liquid to the first heat exchanger, this portion constituting the liquid flow and means for sending at least a portion of the vaporized liquid flow from the first heat exchanger to the bottom of the distillation column to separate there or to a product compressor (C3, C4) to serve as product or to a liquid flow (55) withdrawn from the distillation column.,

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