Method and apparatus for separating a mixture containing CO2

Abstract

The present invention relates to a method for separating a gas mixture (1) having a dew point of 0 to 15°C at a first pressure, wherein the gas mixture contains carbon dioxide and at least one first component heavier than carbon dioxide, and the method comprises the steps of cooling the mixture to a first temperature of 0 to 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 pressurized liquid stream (29) vaporizing in a heat exchanger, and 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) from which at least one first component has been depleted, wherein the liquid stream is produced by separating the gas phase.

Description

Technical Field

[0001] The present invention relates to a process and an apparatus for separating a mixture containing CO2 and at least one first component heavier than carbon dioxide. The mixture has a dew point of 0 °C to 15 °C at a first pressure.

Background Art

[0002] The capture of CO2 by a process operating at low temperature may involve the use of a refrigerant to condense at least one component heavier than carbon dioxide, such as water, present in the gas to be treated. This step makes it possible to significantly reduce the content of at least one component heavier than the carbon dioxide of the gas before the gas passes through the adsorbent to remove the last traces of condensable molecules.

[0003] The capture of carbon dioxide (CO2) by a partial condensation and / or distillation process operating below 0 °C generally requires drying the wet CO2-enriched gas to be treated upstream of the low-temperature separator to remove condensable molecules, mainly water (H2O), in order to avoid any risk of freezing. This drying is often split into two steps. First, the gas is cooled in one or more heat exchangers to condense most of these molecules, and then this CO2-enriched gas passes through an adsorbent to remove the last traces of condensable molecules.

[0004] Those skilled in the art know that the cold air required to condense the water in the wet CO2-enriched gas is often generated by a refrigeration unit. A heat transfer fluid (Freon (registered trademark), ammonia, propane, and the like) is used to transfer this cold air to a cold water loop and then to the wet CO2-enriched gas.

[0005] GB-A-2 416 389 describes a process for cooling wet CO2, in which compressed wet CO2 is first cooled by seawater in a first heat exchanger, and then cooled by two flows of gaseous CO2 in a second heat exchanger, in order to condense the water contained in the CO2 upstream of the adsorption unit. This water is removed using a phase separator downstream of the two exchangers.

[0006] Refrigerated units connected to a chilled water loop, such as those in the first exchanger of GB-A-2 416 389, are expensive and not very efficient equipment items. This invention provides an improvement to the CO2 capture process by implementing thermal integration to cool the humid gas supplied to the CO2 capture process. As a result, the refrigerated unit and its chilled water network may no longer be necessary or may be reduced in size.

[0007] US2020 / 309451 describes a process in which all liquids produced by a CO2 separation process are used to condense water in the flow to be separated. The liquids remain in liquid or supercritical form before being supplied to the pipes. If only perceptible heat is used to condense the water, a large amount of liquid, in this case all liquid products of the process, must be sent to a heat exchanger.

[0008] Aspelund et al., in "Gas conditioning—The interface between CO2 capture and transport," published in the International Journal of Greenhouse Gas Control, 2007, pp. 343-354, describes a CO2 separation process in which water condenses through heat exchange with a CO2-enriched fluid produced by distillation. In reality, these fluids all appear to be in gaseous form.

[0009] Furthermore, the exchanger for cooling the humid gas performs the exchange between only two fluids.

[0010] The cold air required to condense water or another component with a relatively high condensation temperature is drawn directly from part of a process operating at low temperatures, via at least a portion of the generated liquid CO2. This invention applies when the CO2 capture unit produces CO2 in gaseous or liquid or dense phase. This is because, whatever state the generated CO2 is in, the cryogenic separation process always passes through a liquid phase (a liquid resulting from partial condensation and / or from a distillation column and / or from the cycle in the case of liquid production).

[0011] According to one of the alternative embodiments, the present invention consists of: 1) Condensation of water due to the evaporation of CO2 • Cooling a pressurized, humid gas enriched with CO2 and H2O in a heat exchanger by indirect heat exchange to a temperature of 0°C to 15°C, and partially condensing the water it contains through the vaporization of a CO2-enriched liquid, such as pressurized liquid CO2. • Separating liquid water from cooled, pressurized, and humid gas. 2) Preparation of liquid CO2 The cold air necessary to partially condense this moist CO2-enriched gas is provided by a stream of liquid CO2 that originates from a part of the process operating at low temperatures and vaporizes in the exchanger. This stream of liquid CO2 is drawn from a part of the liquid liquefaction or from a part of the liquid production in a distillation column and / or a part of the partial condensation and / or a part of the cycle in the case of separation producing liquid, pumped (if necessary) to obtain a pressure of 30-50 bara, then de-subcooled (if necessary) in the main exchanger of the cryogenic unit to obtain a temperature of -5°C to 15°C, and sent into the heat exchanger. These temperatures and pressures are chosen to avoid any risk of water freezing in the exchanger. 3) Recovery of gaseous CO2 obtained CO2 exits the heat exchanger at a temperature of 5°C to 80°C, preferably 20°C to 40°C, and is returned to the CO2 compressor stage, or, if the pressure of the gaseous CO2 is lower than the pressure of the CO2 evaporating in the heat exchanger, is returned directly to the generated gaseous CO2. In this way, energy savings are achieved in the compression of CO2. Step 2) De-subcooling can be carried out by mixing pumped liquid CO2 with higher temperature CO2 to obtain a temperature of -5°C to 15°C. This makes it possible to avoid passing through the main exchanger of the cryogenic unit.

[0012] This invention makes it possible to eliminate both refrigeration units and chilled water loops by utilizing some potentially excess cold air that operates at low temperatures. This reduces the number of equipment items required, and consequently the cost, as well as the energy consumption of this CO2 capture process (savings on energy consumption of refrigeration units and savings on compression of pumped CO2).

[0013] According to the subject of the present invention, a process for separating a gas mixture having a dew point of 0°C to 15°C at a first pressure and containing carbon dioxide, at least one first component heavier than carbon dioxide, and optionally at least one second component lighter than carbon dioxide, i) To obtain a two-phase mixture by indirect heat exchange with a pressurized liquid stream, the gas mixture is cooled at a first pressure to a temperature of 0°C to 15°C, and the first component of the gas mixture is at least partially condensed in a first heat exchanger. ii) Separating the liquid phase of a cooled two-phase mixture in order to obtain a liquid phase containing at least one first component and a gaseous phase from which at least one first component has been depleted, iii) A step of cooling the gas phase or a gas derived from the gas phase in a second heat exchanger, iv) Either of the following liquefaction or separation steps, i.e., a) A step of liquefying the cooled gas phase in order to produce a CO2-enriched liquid, or b) To produce a gas mixture enriched with CO2 and optionally depleted of at least one second component, the gas is separated from the cooled gas phase or the gas derived from the cooled gas phase by partial condensation and / or distillation. Equipped with, v) A process is provided in which the liquid stream of step i) constitutes a portion of the CO2-enriched liquid or the CO2-enriched liquid of step iv a) or b), or a portion of the liquid derived therefrom, wherein the pressurized liquid stream is preferably vaporized in a first heat exchanger.

[0014] The liquid stream preferably contains at least 95 mol% CO2.

[0015] According to other optional embodiments of the present invention, • At least one first component is water, methanol, or ammonia. The second component, if present, is nitrogen, oxygen, hydrogen, carbon monoxide, or methane. The CO2-enriched liquid is at least part of the liquid at the bottom of the distillation column. The CO2-enriched liquid is at least part of the liquid in the phase separator. • The CO2-enriched liquid is at least part of the liquid in the phase separator. The CO2-enriched liquid is pressurized by a pump to a pumping pressure of 30-50 bara before being sent to the first heat exchanger, and then heated to a temperature of -5°C to 10°C. The CO2-enriched liquid is produced from the CO2 cycle, and part of that cycle operates under a second pressure, preferably higher than 30 bara, and actually higher than 46 bara. The CO2-enriched liquid is cooled to a temperature of -5°C to 10°C without any change in state, and then expanded to a third pressure of 30 to 46 bara. The CO2-enriched liquid resulting from liquefaction or partial condensation and / or distillation is vaporized in a 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 generated gaseous CO2. • Another liquid is a fraction of the liquid at the bottom of the tower. The liquid enriched with CO2 vaporized in the first heat exchanger is optionally sent to a CO2 compressor at pumping pressure or a third pressure, or directly into the generated gaseous CO2, or to a distillation column, or to the liquid product of the distillation column. • Another liquid enriched with CO2 is sent to the second heat exchanger at a pressure lower than the pressure of the CO2-enriched liquid sent to the first heat exchanger. The gas mixture is cooled upstream of the first heat exchanger by heat exchange with water or another refrigerant. The gas derived from the gas phase is formed by separating the gas phase by adsorption, permeation, and / or partial condensation and / or distillation. The gas derived from the gas phase is separated from it, for example by adsorption or permeation, in order to reduce its content of at least one lighter component. The gas derived from the gas phase is then extracted from it by compression and drying. • The first heat exchanger performs indirect heat exchange between only two fluids. • The CO2-enriched liquid contains at least 95% CO2 and is produced by partially condensing the cooled gas phase. The CO2-enriched vaporized liquid is sent to be mixed with the gas phase upstream of the partial condensation and / or distillation step, and the liquid derived from the CO2-enriched liquid or the CO2-enriched liquid is derived therefrom by purification and / or pumping and / or expansion. The liquid stream completely vaporizes in the first heat exchanger. The liquid at the bottom of the column is preferably vaporized in the second exchanger without being compressed or expanded, and the vaporized liquid is at least partially delivered into the bottom of the column in a gaseous form. · The bottom liquid of the column preferably vaporizes in the second exchanger without being compressed or expanded, and the vaporized liquid is sent partially into the bottom of the column in gaseous form and partially to the product compressor. · The liquid stream sent to the first heat exchanger constitutes 5% - 15% of the bottom liquid of the column. · A part of the CO₂ - enriched liquid vaporizes by indirect heat exchange with the mixture cooled in step i) to form a vaporized liquid stream, and the vaporized liquid stream is sent at least partially into the bottom of the column in gaseous form so as to be separated in the column. · The depleted, e.g., dried mixture is cooled in the second heat exchanger, in which the vaporized liquid stream is cooled. · The CO₂ - depleted stream is cooled in the second heat exchanger, in which the vaporized liquid stream is cooled. · The depleted, e.g., dried mixture is cooled in the second heat exchanger, in which the vaporized liquid stream is not cooled. · The CO₂ - depleted stream is cooled in the second heat exchanger, in which the vaporized liquid stream is not cooled. · The vaporized liquid stream is sent into the bottom of the distillation column and / or is not cooled before being mixed with the CO₂ - enriched liquid pressurized by a pump. · The depleted, e.g., dried mixture, or the CO₂ - depleted stream is cooled in the second heat exchanger, in which a part of the CO₂ - enriched liquid is heated before step v). · Another part of the CO₂ - enriched liquid is heated and vaporized in the second heat exchanger and sent into the bottom of the column in gaseous form so as to be separated in the column. · Another part of the CO₂ - enriched liquid vaporizes in the second heat exchanger and is sent to the customer without being compressed. · A fraction of the CO₂ - enriched liquid is pressurized by a pump, and a part of the pressurized liquid constitutes the liquid used to cool the mixture in step i). · A part of the pressurized liquid is expanded to form a liquid product. The vaporized flow is delivered in a gaseous form at a first temperature so that at least a portion of it mixes with a portion of a pressurized liquid intended to act as a product at a second temperature lower than the first temperature.

[0016] According to another subject of the present invention, an apparatus for separating a gas mixture having a dew point of 0°C to 15°C at a first pressure and containing carbon dioxide, 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 gas mixture at a first pressure so that it is cooled in the first heat exchanger by indirect heat exchange to a temperature of 0°C to 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; and removal of the condensed portion of the first component of the gas mixture. An apparatus is provided comprising means for doing so, means for sending a gas phase depleted of at least one first component to a second heat exchanger so as to be cooled, means for separating the cooled gas phase in the second heat exchanger comprising a distillation column, means for discharging the CO2-enriched liquid from the distillation column, and means for sending a portion of the CO2-enriched liquid to the first heat exchanger, where this portion constitutes a liquid stream, and means for sending at least a portion of the vaporized liquid stream from the first heat exchanger to the bottom of the distillation column so as to be separated in the distillation column, or to a product compressor so as to act as a product, or to a liquid stream drawn out of the distillation column.

[0017] Preferably, the apparatus comprises means for pressurizing a flow of CO2-enriched liquid drawn out at the bottom of the tower to form a pressurized flow, and means for sending a portion of the vaporized liquid stream from the first heat exchanger to be mixed with the pressurized liquid flow.

[0018] Preferably, to form a pressurized flow, means for pressurizing the flow of CO2-enriched liquid drawn out at the bottom of the tower are connected to means for splitting the liquid into two downstream of a second heat exchanger, forming a first and second portion of the liquid, and the apparatus comprises means for delivering the first portion of the liquid, connected to the first heat exchanger, and means for delivering the second portion of the liquid from the second heat exchanger to be mixed with the bottom liquid.

[0019] The present invention will be described in more detail with reference to the figures. [Brief explanation of the drawing]

[0020] [Figure 1] This represents the process according to the present invention. [Figure 2] This represents the process according to the present invention. [Figure 3] This represents the process according to the present invention. [Figure 4] This represents the process according to the present invention. [Figure 5] This represents a part of the process according to the present invention. [Figure 6] Figure 5 shows a continuation of the process according to the present invention. [Figure 7] Figure 5 shows a continuation of the alternative process according to the present invention. [Modes for carrying out the invention]

[0021] In Figure 1, gas mixture 1 at a first pressure contains carbon dioxide, at least one first component having a condensation point of 0°C to 15°C at the first pressure, such as water, methanol, and ammonia, and at least one second component lighter than carbon dioxide, such as nitrogen, oxygen, hydrogen, methane, or carbon monoxide. Gas mixture 1 may also contain components heavier than carbon dioxide.

[0022] The gas mixture 1 is at a temperature of 5°C to 25°C. It is sent to a first heat exchanger E1, where the first heat exchanger E1 indirectly exchanges heat with a flow of liquid CO2 29 so that it cools down to a temperature of 0°C to 15°C, and the mixture 1 remains at a first pressure.

[0023] At least one first component contained in the gas mixture is condensed to form a condensate H, for example, condensed water, which is removed in the phase separator S1. The gas 3, enriched with CO2 and depleted of at least one first component, is compressed in the compressor C1, dried in the dryer D to remove the remaining water, and then formed a flow 5 which is compressed in the compressor C2 to a pressure of 15-65 bara. The flow 7 compressed in the compressor C2 is sent to a second heat exchanger E2 to be partially condensed, forming a two-phase flow 9. The flow 9 is separated in the separator S2 into a gas 11 which is depleted of CO2 and enriched with at least one second component, and a liquid 13 which is depleted of at least one second component and enriched with CO2.

[0024] Switches E2 and E3 can constitute a single switch.

[0025] Liquid 13 is expanded and sent to the top of the distillation column K.

[0026] The gas 11 is partially condensed in the third heat exchanger E3, forming a two-phase flow that is separated in the phase separator S3, forming a gas 17 in which CO2 is depleted and enriched with at least one second component, and a liquid 15 in which at least one second component is depleted and enriched with CO2.

[0027] The gas 17 is heated in the third and second heat exchangers E3 and E2. The liquid 15 is expanded and sent to the top of the tower K.

[0028] The top gas 21 from tower K is heated in the third and second heat exchangers E3 and E2, then sent between compressors C1 and C2 and mixed with flow 5.

[0029] The liquid 19 at the bottom of tower K is drawn out as a flow 19 enriched with CO2 and depleted of at least one second component. The liquid 19 is divided into two parts 23 and 25. Part 23 is expanded in a valve to form a two-phase flow that is separated in phase separator S4. The liquid 35 from separator S4 is vaporized in either the second or third exchanger, and the gas 33 from separator S4 is heated in the second and third exchangers. The two heated gases thus formed are mixed and compressed in series in compressors C3 and C4 to form a flow 37 in which CO2 in gaseous form is enriched into a product 41.

[0030] Part 25 is separated to form part 29, and the remaining part 27 of this part vaporizes in the second heat exchanger E2 before being sent into the bottom of tower K, providing re-boiling in the form of a gaseous flow.

[0031] A portion of flow 27 may be sent to compressor C3.

[0032] Portion 29 is pressurized by pump P to a pressure of 30-50 bar abs, and then the pressurized portion of portion 29 is heated in exchanger E2, and in fact even vaporized, while the remaining portion of the pressurized portion 29 does not enter exchanger E2. The portion sent to exchanger E2 and the remaining portion not sent to exchanger E2 are mixed to obtain liquid CO2 with the desired subcooling. This mixture is sent at a temperature of -5°C to 10°C to vaporize in the first heat exchanger E1 by heat exchange with flow 1 only.

[0033] Temperatures of -5°C to 10°C can be achieved by mixing the pumped liquid CO2 with warmer CO2 (e.g., some of the CO2 produced 39, 41).

[0034] Part 29 vaporizes in the first exchanger E1, and the formed gas is sent to a point between compressors C3 and C4 at a temperature of 5°C to 40°C, where it is mixed with the compressed flow 39 in compressor C3, and the outlet pressure of compressor C3 is 15 to 46 bar, which is less than the pumping pressure of part 29.

[0035] In an alternative configuration, the first exchanger E1 can be located between the compressors C1 and C2.

[0036] The gas purified by the condensation of the first component in the exchanger E1 can be dried, for example, by a TSA in adsorption units downstream of the phase separator S1 and upstream of the compressor C1.

[0037] In an alternative configuration, the liquid CO2 supplied to the first heat exchanger E1 may originate from a refrigerated cycle in which carbon dioxide circulates. This cycle can provide cool air for a partial condensation and / or distillation process. Part of the cycle operates under a second pressure, preferably higher than 30 bara, and in practice higher than 46 bara. The liquid in the cycle is cooled to a temperature of -5°C to 10°C without a change of state, expanded to a third pressure of 30 to 46 bara, and then supplied to the first heat exchanger E1 as flow 29.

[0038] In an alternative configuration, gas 3 or the gas produced therefrom may be separated in a pressure swing adsorption (PSA) unit to generate low-pressure and high-pressure products compressed in the compressor C1.

[0039] In the alternative configuration, gas 3 is sent to the exchanger E2 without intermediate compression.

[0040] According to an alternative configuration, Figure 1 may include, for example, a separation step by adsorption upstream of the compressor C1 to reduce the content of gas phase 3 in at least one lighter component.

[0041] The liquid stream 29 sent to the first heat exchanger constitutes 5% to 15% of the liquid 19 at the bottom of tower K in Figures 1 to 3.

[0042] Figure 2 illustrates this alternative configuration in which purified gas 3, free of water and / or methanol and / or ammonia H, is separated by an adsorbent A upstream of a four-stage compressor C1. The adsorbent produces gas 3B enriched with at least one lighter component and depleted of CO2, and gas 3A enriched with CO2 and depleted of at least one lighter component. Gas 3A is then compressed in compressor C1, dried in dryer D, for example by TSA, and compressed in three-stage compressor C2. The number of stages in compressors C2 and C3 is obviously variable.

[0043] Another difference from Figure 1 is that some of the vaporized gas 27 28 in the exchanger E2 is sent to the product compressor at a higher pressure than the pressure of flows 33 and 35. Thus, flows 33 and 35 are first compressed in compressor C3, then mixed with flow 28 and compressed in compressor C3'. The vaporized liquid 29 is mixed with the gas from compressor C3', and the mixture is compressed in compressor C4.

[0044] Figure 3 shows a version of Figure 1 without the adsorption unit A, but with compression of part of the gas 27 28.

[0045] Figure 4 illustrates the process according to the present invention, wherein the heat exchanger E1 provides the necessary cool air to condense at least one first component, such as water, which is at least a portion of the feed flow that is removed after drying in the exchanger E1, and preferably after drying by adsorption. The liquid 29 forms a portion of the liquid condensed in the phase separator S2, which is produced by the partial condensation of the flow 9 that is compressed in the compressors C1, C2 and cooled in the exchanger E2. The liquid 29 may otherwise be removed from the separator S3.

[0046] Liquid 29 is expanded in the valve, then vaporizes in the heat exchanger E1, and is returned in gaseous form between compressors C1 and C2 to compensate for the pressure drop in the pipe and exchanger E1 by compression in C2. The rest of the figure is unchanged from Figure 1.

[0047] Alternatively, a portion of the liquid 15 is used to cool the heat exchanger E1 in order to condense at least one first component.

[0048] Liquid 29 preferably contains at least 95 mol% CO2.

[0049] In alternative configurations not illustrated, a gaseous mixture containing carbon dioxide and at least one first component heavier than carbon dioxide, having a dew point of 0°C to 15°C at a first pressure, is cooled in a first heat exchanger to a temperature of 0°C to 15°C at a first pressure. 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 vaporizing 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 of at least one first component. The gas phase is cooled and liquefied in a second heat exchanger to form a CO2-enriched liquid containing at least 95 mol% CO2. A portion of this liquid is used as a liquid stream to condense at least one first component in the first heat exchanger.

[0050] According to an alternative configuration, Figure 4 may include, for example, a separation step by adsorption upstream of the compressor C1 to reduce the content of gas phase 3 in at least one lighter component.

[0051] Figures 5-7 illustrate a new method using a vaporized fluid when the refrigerant is found to be high-pressure liquid CO2.

[0052] In the context of optimizing capital costs, and perhaps especially for units handling small amounts of gas, it is possible to consider a scheme without a product compressor at an optional cost. This change leads to a rethinking of where the high-pressure CO2 vaporized in the gas condenser is recycled.

[0053] However, the processes shown in Figures 5-7 are also applicable to processes involving a product compressor.

[0054] In Figure 5, a gas mixture 1 containing carbon dioxide and at least one component heavier than carbon dioxide, such as water, and at least one component lighter than carbon dioxide, is cooled in a heat exchanger E1 to condense at least a portion of the heavier components it contains, such as water and / or methanol and / or ammonia, to form a dried mixture. Preferably, the heavier components, such as water, are condensed by indirect heat exchange in the heat exchanger E1 with only one flow, namely, a CO2-enriched liquid flow 29 resulting from the separation of the dried mixture. The CO2-enriched liquid flow then vaporizes.

[0055] Gas 3 is dried in dryer D and then separated by one of the processes illustrated in Figures 6 and 7.

[0056] A first alternative embodiment of the present invention is illustrated in Figure 6. It involves using the CO2-enriched vaporized liquid directly as the reboiling gas in the cryogenic section of the distillation column. Very frequently, this dry gas flow is insufficient to enable effective reboiling, and thus would only serve as a supplement to the conventional reboiling source, which consists of some of the vaporized liquid CO2 in the main heat exchanger. Figure 6 shows this new configuration in a section operating at low temperatures. This alternative embodiment thus allows for the efficient recycling of vaporized CO2, particularly when the process does not have a product compressor. However, the present invention may also be applicable when such a compressor exists, and thus simply allows for a reduction in the flow of the vaporized liquid in the main heat exchanger that is sent into the column.

[0057] A gas mixture 3, in which at least one heavier component H and optionally at least one lighter component in which its content is reduced (e.g., by adsorption), is cooled in a second heat exchanger E2, where the gas mixture 3 is partially condensed. The two-phase flow is drawn out of the heat exchanger E2 at an intermediate level and sent to a phase separator S2. The formed liquid is sent to the top of the tower K, and the formed gas is cooled in the second heat exchanger E2 so as to be partially condensed. The formed flow is separated in a phase separator S3, the gas 17 is heated in the heat exchanger E2, and the liquid is sent to the top of the tower K. The gas 17 can then be separated by permeation in known ways.

[0058] The liquid sent to tower K is separated to form a gas 21 enriched with at least one component lighter than CO2 and a liquid 19 enriched with CO2. Gas 21 is heated in 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. Liquid 19 is divided into two parts, one part of which is divided to form a flow 27, which is vaporized in a second heat exchanger E2 and used as the re-boiling gas of tower K without being cooled in heat exchanger E2. The other liquid flow is expanded to form a two-phase flow that is separated in phase separator S4. The formed gas 33 and liquid 35 are heated and vaporized when the liquid and gas are mixed to form a gas. This gas can be used as a product after or without compression in a compressor. Another part of the bottom liquid 19 is pressurized by a pump, for example, to at least 30 bar abs. A portion of the pressurized liquid 29 in pump P vaporizes in heat exchanger E2 and is used to vaporize itself and cool the first heat exchanger E1. The vaporized liquid is mixed with the gas 27 produced from the vaporization of the liquid downstream of heat exchanger E2, and the mixture is used as the reboiling gas for the tower.

[0059] A portion of the pressurized liquid 51 is heated in the heat exchanger E2 and mixed with the pressurized liquid used to heat it, forming liquid 55 as a product. The pressurized liquid that is not sent to the heat exchanger E2 must be slightly expanded to compensate for the pressure drop of the portion 51 that rejoins the heat exchanger E2 to form liquid 55.

[0060] The refrigeration cycle using propane (PR) plays a role in generating the cold air necessary for the process that produces a certain proportion of CO2 in liquid form.

[0061] The short circuit 31 allows for a change in the temperature of the liquid 29 supplied to the first heat exchanger E1.

[0062] A second alternative embodiment of the present invention is illustrated in Figure 7. This is an alternative embodiment of Figure 6, and only elements different from those in Figure 6 are identified in the figure for clarity. It involves supplying gaseous CO2 not only as a reboiling product in the distillation column but also as a heat source to "de-subcool" the liquid product. This is because, particularly in the context of high-pressure (>30 bara) liquid production, the liquid drawn at the bottom of the distillation column and then pumped to the production pressure is too cold to be stored or transported under normal conditions (often referred to as a subcooling of 2°C above equilibrium temperature). This scheme provided in Figure 7 makes it possible to heat the product while significantly reducing energy consumption compared to the scheme in Figure 6, in the context of high-pressure production.

[0063] A portion of the liquid vaporized in the first heat exchanger E1 is sent to the tower K as a re-boiling gas, and another portion of the vaporized liquid 29A is drawn from the bottom of the tower K and mixed with liquid 55 that has been pressurized by a pump to at least 30 bar abs. Thus, a portion of the vaporized flow 29A is mixed with a portion of the pressurized liquid 55 that is intended to be delivered in gaseous form at a first temperature and act as a product at a second temperature lower than the first temperature. The resulting mixture 57 constitutes a liquid that has been de-subcooled to at least 30 bar abs. This feature can be utilized when a portion of the vaporized liquid is not sent from the first heat exchanger E1 to the tower K.

[0064] A portion of the liquid vaporized in the first heat exchanger E1 is not sent to tower K as a re-boiling gas, and another portion of the vaporized liquid 29A is not mixed with the liquid 55 drawn from the bottom of tower K, but is cooled downstream of the first heat exchanger E1.

[0065] As explained above, the gaseous mixture dried in the dryer can be sent directly to the cryogenic separator without being separated between the dryer and the cryogenic separator by pressure swing adsorption.

[0066] Otherwise, the gas mixture dried in the dryer can be directly separated by pressure swing adsorption between the dryer and a cryogenic separator. Separation by adsorption forms a gas enriched with at least one lighter component, e.g., hydrogen and / or nitrogen, and a gas depleted of this component. The gas depleted of this component, which is lighter than CO2, can be enriched with CO2, compressed in a compressor, and separated by partial condensation and distillation.

[0067] In the version shown in Figure 7, the heated liquid 51 is absent and is not returned to the liquid being pumped in pump P. A valve is illustrated in this figure, which may be present, for example, to equalize the pressure between the liquid pressurized by pump P and the flow 29A.

[0068] This is because, in this particular case, sending all the flow coming from the first heat exchanger E1 to the reboiled material in tower K increases the amount of CO2 recycled to the compressor, and consequently increases the energy consumption of the compressor.

[0069] A portion of the gas 29A is not sent to the heat exchanger E2, either before or after mixing with the pressurized liquid.

Claims

1. A process for separating a gas mixture (1) having a dew point of 0°C to 15°C at a first pressure and containing carbon dioxide, at least one first component heavier than carbon dioxide, and optionally at least one second component lighter than carbon dioxide, i) Cooling the gas mixture to a temperature of 0°C to 15°C in order to obtain a two-phase mixture by indirect heat exchange with a pressurized liquid stream (29), and condensing at least partially the first component of the gas mixture in a first heat exchanger (E1), ii) Separating the cooled liquid phase (H) of the two-phase mixture in order to obtain a liquid phase containing at least one first component and a gas phase (3) from which at least one first component has been depleted, iii) A step of cooling the gas phase (3) or the gases (3A, 5) derived from the gas phase in a second heat exchanger (E2), iv) Either of the following liquefaction or separation steps, a) CO 2 To produce an enriched liquid, the steps include liquefying the cooled gas phase, or b) CO 2 To produce a liquid (13, 15, 19, 25, 29) enriched and optionally depleted of at least one of the second components, one of the steps of separating the cooled gas phase or the gas derived from the cooled gas phase by partial condensation and / or distillation is performed. Equipped with, v) The liquid stream in step i) is the CO in step iv a) or b). 2 enriched liquid or CO 2 This constitutes part of the enriched liquid or part of the liquid derived therefrom, and the liquid stream preferably contains at least 95 mol% CO 2 In a process that contains, The process is characterized in that the liquid stream vaporizes in the first heat exchanger.

2. The process according to claim 1, wherein at least one of the first components is water, methanol, or ammonia.

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

4. The aforementioned CO 2 The process according to any one of claims 1 to 3, wherein the enriched liquid (29) is at least a portion of the bottom liquid (19) of the distillation column (K).

5. The aforementioned CO 2 The process according to any one of claims 1 to 4, wherein the enriched liquid (29) is pressurized by a pump (P) to a pumping pressure of 30 to 50 bar before being sent to the first heat exchanger, and then heated to a temperature of -5°C to 10°C.

6. Said CO 2 enriched liquid (29) results from the CO 2 cycle, a part of said cycle operating at a second pressure which is preferably higher than 30 bara and in fact higher than 46 bara, of the process according to any one of claims 1 to 4.

7. The aforementioned CO 2 The process according to claim 6, wherein the enriched liquid (29) is cooled to a temperature of -5°C to 10°C without a change of state, and then expanded to a third pressure of 30 to 46 bara.

8. CO generated from the liquefaction or partial condensation and / or distillation 2 Another liquid (23) enriched with CO vaporizes in the second heat exchanger (E2) and is acquired at the outlet of the second heat exchanger. 2 The enriched gas (37) is CO 2 Gaseous CO2 is sent to the compressors (C3, C4) or generated. 2 The process described in any one of claims 1 to 7, which is sent directly into the container.

9. The CO vaporized in the first heat exchanger (E1) 2 The enriched liquid (19, 29, 29A) is optionally pumped at the aforementioned pumping pressure or the third pressure and the CO2 2 Gaseous CO2 is sent to the compressors (C3, C4) or generated. 2 The process according to any one of claims 1 to 8, wherein the product is sent directly into the distillation column (K), or to the liquid product (55) of the distillation column.

10. The aforementioned CO 2 Another liquid (23) enriched with CO is sent to the first heat exchanger (E1) 2 The process according to claim 8, wherein the enriched liquid (20) is sent to the second heat exchanger (E2) at a pressure lower than the pressure of the enriched liquid (20).

11. The process according to any one of claims 1 to 10, wherein the gas mixture (1) is cooled upstream of the first heat exchanger (E1) by heat exchange with water or another refrigerant.

12. The process according to any one of claims 1 to 11, wherein 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. The process according to any one of claims 1 to 12, wherein the first heat exchanger (E1) performs indirect heat exchange between only two fluids (1, 29).

14. The aforementioned CO 2 The enriched liquid (29) contains at least 95% CO 2 The process according to any one of claims 1 to 13, which is produced by partially condensing the cooled gas phase (7) containing (S2, S3).

15. An apparatus for separating a gas mixture (1) having a dew point of 0°C to 15°C at a first pressure, and containing carbon dioxide, at least one first component heavier than carbon dioxide, and optionally at least one second component lighter than carbon dioxide, The first heat exchanger (E1), A second heat exchanger (E2), and means for supplying the gas mixture at the first pressure so that it is cooled in the first heat exchanger by indirect heat exchange to a temperature of 0 to 15 degrees Celsius in order to obtain a two-phase mixture by indirect heat exchange, Means for sending a pressurized liquid stream (29) to the first heat exchanger, Means for removing the condensed portion (H) of the first component of the gas mixture, Means for supplying a gas phase (3) in which at least one first component has been depleted to the second heat exchanger so as to be cooled, Means for separating the gas phase cooled in the second heat exchanger, which is equipped with a distillation column (K), CO 2 Means for discharging the enriched liquid (19), The CO2 is supplied to the first heat exchanger. 2 Means for delivering a portion of the enriched liquid, where this portion constitutes the liquid stream. An apparatus comprising means for sending at least a portion of the vaporized liquid stream from the first heat exchanger to the bottom of the distillation column so as to be separated in the distillation column, or means for sending it to product compressors (C3, C4) so ​​as to act as a product, or means for sending it to a liquid stream (55) drawn out of the distillation column.

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