Method and apparatus for separating a mixture containing CO2
By integrating thermal integration to utilize the excess cold from the low-temperature CO2 capture process, the need for refrigeration units and cold water loops is eliminated, significantly reducing energy consumption and costs while enhancing CO2 capture efficiency.
Patent Information
- Application Number
- FR2023004898
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-05-17
- Publication Date
- 2025-04-11
- Estimated Expiration
- 2043-05-17
AI Technical Summary
Existing CO2 capture processes require expensive and inefficient refrigeration units and cold water loops to cool wet gases rich in CO2, which increases energy consumption and costs.
The process integrates thermal integration to cool wet gases by using the excess cold from the low-temperature part of the CO2 capture process, eliminating the need for refrigeration units and cold water loops. This is achieved through indirect heat exchange with a liquid CO2 flow in a heat exchanger, allowing for partial condensation of water and other components.
This approach reduces the number of necessary equipment, lowers energy consumption, and decreases costs by utilizing the inherent cold from the CO2 capture process, thereby enhancing the efficiency of CO2 capture.
Smart Images
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Abstract
Description
Title of the invention: Method and apparatus for separating a mixture containing CO2
[0001] 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
[0002] The capture of carbon dioxide (CO2) by a partial condensation and / or distillation process operating at less than 0°C most often requires the drying of the wet gas to be treated, rich in CO2, upstream of the low-temperature separation to eliminate the 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 eliminate the last traces of condensable molecules.
[0003] 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.
[0004] GB-A-2416389 describes a method of cooling wet CO2 in which the 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.
[0005] 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 to 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.
[0006] In addition, the exchanger for cooling the CO2 carries out an exchange between only two fluids.
[0007] 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 by means of at least a portion of the liquid CO2 product. 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 partial condensation and / or from the distillation column and / or from the cycle in the case of liquid production).
[0008] The invention consists, according to one of the variants, of:
[0009] 1) Condensation of water by evaporation of CO2 Cooling 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 condensing the water it contains by vaporizing a liquid rich in CO2, for example pressurized liquid CO2. Separate liquid water from cooled pressurized wet gas.
[0010]
[0011] 2) Conditioning of liquid CO2 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. 3) The recovery of the gaseous CO2 obtained The CO2 exits 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. De-subcooling in step 2) can be achieved by mixing the pumped liquid CO2 with warmer CO2 to achieve a temperature between -5 and 15°C. This avoids a pass through the main exchanger of the cryogenic unit.
[0012] This invention, by using the potentially excess cold from the part operating at low temperature, makes it possible to remove the refrigeration unit as well as the water loop. cold. 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).
[0013] According to an 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:
[0014] 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 which vaporizes in the heat exchanger
[0015] ii) Separation of the liquid phase from the cooled two-phase mixture in order to obtain a liquid phase containing at least a first component and a gaseous phase depleted in at least a first component
[0016] iii) Cooling the gas phase or a gas derived from the gas phase in a second heat exchanger and
[0017] iv) Either liquefaction or separation as follows:
[0018] a) Either liquefaction of the cooled gas phase to produce a liquid rich in CO2
[0019] b) Either 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 possibly depleted in at least one second component compared to the gas mixture and
[0020] v) The liquid stream of step i) is part of the CO2-rich or CO2-enriched liquid of step iv)a) or b) or of a liquid derived therefrom.
[0021] The liquid stream preferably contains at least 95 mol% CO2.
[0022] According to other optional aspects of the 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 a bottom liquid of a distillation column. • the CO2-enriched liquid is at least part of a liquid from a phase separator • the CO2-rich liquid is at least part of a liquid from a phase separator • 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 which operates under a second pressure, preferably greater than 30 bara, or even greater than 46 bara. • 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. • 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. • the CO2-enriched liquid vaporized in the first heat exchanger is sent to the CO2 compressor, possibly at pumping pressure or third pressure or directly into the produced gaseous CO2. • 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. • 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 first exchanger carries out an indirect heat exchange between only two fluids. • CO2-enriched liquid contains at least 95% CO2 and is produced by partially condensing the cooled gas phase. • the liquid enriched with vaporized CO2 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.
[0023] The invention will be described in more detail with reference to the figures where:
[0024] [Fig-1] represents a method according to the invention.
[0025] [Fig.2] represents a method according to the invention.
[0026] In [Fig.l], a gas mixture 1 at a first pressure contains carbon dioxide, at least a 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. Gas mixture 1 may also contain a component heavier than carbon dioxide.
[0027] 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.
[0028] 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 SL. 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.
[0029] Exchangers E2, E3 can constitute a single exchanger.
[0030] The liquid 13 is expanded and sent to the top of a distillation column K.
[0031] 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.
[0032] The gas 17 heats up in the third and second heat exchanger E3, E2. The liquid 15 is expanded and sent to the top of the column K.
[0033] The head 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.
[0034] The bottom liquid 19 of the 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 of the separator S4 vaporizes in one of the second and third exchangers and the gas 33 of 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.
[0035] 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 gas flow.
[0036] A portion of the flow 27 can be sent to the compressor C3.
[0037] Part 29 is pressurized by a pump P 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 which 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 the flow 1
[0038] The temperature between -5 and 10°C can be achieved by mixing pumped liquid CO2 with warmer CO2 (e.g. some of the CO2 produced 39, 41).
[0039] Part 29 has vaporized in the first exchanger E1 and the gas formed is sent at a temperature between 5 and 40°C to a point between the compressors C3, C4 by mixing with the flow 39 compressed in the compressor C3 whose outlet pressure is between 15 and 46 bars and less than or equal to the pumping pressure of part 29.
[0040] Alternatively, the first exchanger E1 may be located between the compressors C1, C2.
[0041] 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 SI and upstream of the compressor CL.
[0042] 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.
[0043] Alternatively, gas 3 or a gas derived 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.
[0044] Alternatively, gas 3 is sent to exchanger E2 without intermediate compression.
[0045] According to a variant, [Fig.l] may comprise a step of separation by adsorption to reduce the content of the gas phase 3 in at least one lighter component, for example upstream of the compressor CL
[0046] [Fig.2] represents a method according to the invention in which the liquid providing the cold required by the heat exchanger El to condense the at least one first component, for example water, is at least 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.
[0047] The liquid 29 is expanded in a valve and then vaporizes in the heat exchanger El and is returned in gaseous form between the compressors C1, C2, to compensate for the pressure loss in the pipes and the exchanger El by the compression in C2. The rest of the figure is unchanged from [Fig.l].
[0048] Alternatively, a portion of the liquid 15 is used to cool the heat exchanger E1 to condense the at least one first component.
[0049] The liquid 29 preferably contains at least 95 mol% CO2.
[0050] In a variant which is 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 in order 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 in order 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.
[0051] According to a variant, [Fig. 2] may comprise a step of separation by adsorption to reduce the content of the gas phase 3 in at least one lighter component, for example upstream of the compressor CL
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 which is water, methanol or ammonia, 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) which vaporizes in the heat exchanger 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 thegas phase or a gas derived (5) 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 a 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 from step i) is part of the CO2-rich or CO2-enriched liquid from step iv) a) or b) or a liquid derived therefrom, the liquid stream preferably containing at least 95 mol% CO2.
2. The method of claim 1 wherein the second component, if present, is nitrogen, oxygen, hydrogen, carbon monoxide or methane.
3. Method according to one of the preceding claims in which the CO2-enriched liquid (29) is at least a part of a bottom liquid (19) of a distillation column (K).
4. 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.
5. Method according to one of the preceding claims 1 to 3 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.
6. Method according to claim 5 in which the CO2-enriched liquid (29) is cooled to a temperature between -5 and 10°C and then expanded to a third pressure between 30 and 46 bara and without change of state.
7. 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.
8. Method according to one of the preceding claims in which the CO2-enriched liquid (19, 29) vaporized in the first heat exchanger (El) is sent to the CO2 compressor (C3, C4), optionally at the pumping pressure or at the third pressure or directly into the CO2 gas produced.
9. A method according to claim 7 wherein the other CO2-enriched liquid (23) is sent to the second heat exchanger (E2) at a lower pressure than the CO2-enriched liquid (20) sent to the first heat exchanger (El).
10. Method according to one of the preceding claims in which the gaseous mixture (1) is cooled upstream of the first heat exchanger (El) by heat exchange with water or another refrigerant.
11. A method according to one of the preceding claims 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.
12. Method according to one of the preceding claims in which the first exchanger (El) carries out an indirect heat exchange between only two fluids (1, 29).
13. 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).
14. Method according to claim 13 in which the vaporized CO2-enriched liquid (29) is sent to mix with the gaseous phase (5) upstream of a partial condensation and / or distillation step.