Process for separating a mixture containing carbon dioxide, at least one component heavier than carbon dioxide and at least one component lighter than carbon dioxide
The method uses high-pressure CO2 vapor to condense and separate heavier components in gas mixtures, improving CO2 separation efficiency and reducing costs by recycling CO2 vapor in both small and large-scale operations.
Patent Information
- Application Number
- FR2024004262
- Authority / Receiving Office
- FR · FR
- Patent Type
- Utility models
- Current Assignee / Owner
- Filing Date
- 2024-04-25
- Publication Date
- 2025-08-29
- Estimated Expiration
- 2034-04-25
AI Technical Summary
Existing methods for separating carbon dioxide from gas mixtures containing heavier and lighter components, particularly water, are inefficient in reducing investment costs and energy consumption, especially in small-scale operations, and lack effective recycling of high-pressure CO2 vapor.
A method and apparatus utilizing high-pressure CO2 vapor as a refrigerant to condense heavier components like water, followed by partial condensation and distillation, with optional drying and cooling stages, to efficiently separate and recycle CO2, reducing energy consumption and investment costs.
The method enhances CO2 separation efficiency and reduces energy consumption and investment costs by effectively recycling CO2 vapor, suitable for both small-scale and large-scale operations with or without a product compressor.
Smart Images
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Abstract
Description
Title of the invention: Method for separating a mixture containing carbon dioxide, at least one component heavier than carbon dioxide and at least one component lighter than carbon dioxide
[0001] The invention relates to a method and apparatus for separating a mixture containing carbon dioxide, at least one component heavier than carbon dioxide, for example water, and at least one component lighter than carbon dioxide.
[0002] The gas mixture preferably has a dew point temperature between 0 and 15°C at a first pressure.
[0003] The capture of CO2 by a process operating at low temperature sometimes involves the use of a refrigerant fluid to condense at least one component heavier than carbon dioxide, for example water, present in the gas to be treated. This step makes it possible to greatly reduce the content of the at least one component heavier than carbon dioxide in the gas before the latter passes through an adsorbent to eliminate the last traces of condensable molecules. This invention proposes a new way of using the vaporized fluid in the case where the refrigerant is high-pressure liquid CO2.
[0004] State of the art
[0005] It is known from US2020 / 309451 to use high pressure liquid CO2 to cool a wet mixture containing CO2 to be treated and to condense part of the water contained in the gas. This process does not include a distillation column.
[0006] Problems solved by the invention
[0007] As part of an optimization of the investment cost, particularly possible on units treating a small quantity of gas, it is possible to consider a scheme possibly without a product compressor. This change leads to rethinking the place where the high-pressure CO2 vaporized in the gas condenser was recycled.
[0008] However, the method according to the invention also applies to methods with a product compressor.
[0009] Description of the invention
[0010] This invention proposes two new ways of using vaporized high pressure CO2 against gas containing at least one component heavier than CO2, for example a humid gas.
[0011] 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, at least one first component heavier than carbon dioxide, for example water, and at least one component lighter than carbon dioxide in which:
[0012] i. The mixture is cooled to the first pressure to condense at least a portion of the at least one first component it contains and form a mixture depleted in the at least one first component
[0013] ii. The mixture depleted in at least one first component
[0014] is optionally dried in a dryer
[0015] iii. The mixture depleted in at least one first component
[0016] is optionally separated to form a flow depleted in CO2 relative to the dried mixture
[0017] iv. The dried mixture or the CO2-depleted stream is cooled and then separated by partial condensation and in a distillation column and optionally by solidification forming a CO2-enriched liquid.
[0018] v. A portion of the CO2-enriched liquid is used to cool the mixture in step i)
[0019] Characterized in that 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.
[0020] According to other optional aspects: • the depleted mixture, for example dried, is cooled in a second heat exchanger in which the flow of vaporized liquid cools. • the CO2-depleted flow is cooled in a second heat exchanger in which the vaporized liquid flow is cooled. • the depleted mixture, for example dried, is cooled in a second heat exchanger in which the flow of vaporized liquid does not cool • the CO2-depleted flow is cooled in a second heat exchanger in which the vaporized liquid flow is not cooled. • 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 • 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 CO2-enriched liquid heats up and vaporizes in the second heat exchanger and is sent to the column bottom in gaseous form to separate there. • another part of the CO2-enriched liquid vaporizes in the second heat exchanger and is sent to a customer without having been compressed. • 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). • part of the pressurized liquid is expanded to form a liquid product. • at least part of the vaporized flow is sent in gaseous form to a first temperature to mix with a portion of the pressurized liquid intended to serve as product which is at a second temperature, lower than the first temperature.
[0021] 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 bottom of the distillation column to separate there.
[0022] 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.
[0023] 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 splitting 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 tank liquid.
[0024] The invention will be described in more detail with reference to the figures where:
[0025] [Fig-1] illustrates the part of the process where water in the gas mixture is condensed.
[0026] [Fig.2] illustrates one way of using the CO2-enriched liquid used by condensing at least one component heavier than carbon dioxide, e.g., water, in [Fig.l],
[0027] [Fig.3] illustrates an alternative way of using the CO2-enriched liquid used by condensing at least one component heavier than carbon dioxide, e.g., water, in [Fig.l].
[0028] In [Fig.l], 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, which it contains and to form a dried mixture. Preferably the water is condensed by indirect heat exchange in the heat exchanger E1 with only one flow, a liquid flow 29 enriched in CO2 coming from the separation of the dried mixture. The liquid flow enriched in CO2 is vaporized.
[0029] The gas 3 is dried in a dryer D and then separated by one of the processes illustrated in [Fig.2] and [Fig.3].
[0030] A first variant of the invention is illustrated in [Fig.2]. It consists of using the vaporized CO2-enriched liquid in its entirety as reboiling gas for a distillation column of 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 part of the vaporized liquid CO2 in the main heat exchanger. [Fig.2] shows this new configuration of the cryogenic section. This invention 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.
[0031] The gas mixture 3 whose content has been reduced in at least one heavier component H and possibly in 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 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 whose gas 17 heats up in the heat exchanger E2, the liquid being sent to the top of column K. The gas 17 can then be separated by permeation, in a known manner.
[0032] 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 reboiling gas for 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 part of the tank liquid 19 is pressurized by a pump, for example up to at least 30 bar abs. A part 29 of the liquid pressurized 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.
[0033] A portion 51 of the pressurized liquid is heated in the heat exchanger E2 and is mixed with the pressurized liquid to heat it, forming a liquid 55 as a 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.
[0034] A refrigeration cycle using PR propane is used to produce the cold required for the process which produces a percentage of the CO2 in liquid form.
[0035] A short-circuit circuit 31 makes it possible to vary the temperature of the liquid 29 sent to the first heat exchanger EL.
[0036] A second variant of the invention is illustrated in [Fig.3]. This is a variant of [Fig.2] and only the elements different from those of [FIG.2] are identified in the figure, for clarity. It consists of sending the CO2 gas both as reboiling of the distillation column but also as a source of heat 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 normal conditions (we often speak of 2°C of subcooling compared to the equilibrium temperature). Thanks to this diagram proposed in [Fig.3], it is thus possible to heat the production while greatly reducing energy consumption compared to the diagram in [Fig.2] in the context of high-pressure production.
[0037] 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 bars 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 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 bars 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.
[0038] Neither the part of the vaporized liquid in the first heat exchanger El 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 El.
[0039] 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.
[0040] Alternatively, the gas mixture dried in the dryer directly can be separated 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, for example hydrogen and / or nitrogen, and a gas depleted in this component. The gas depleted in this component lighter than CO2 is enriched in CO2 and can be compressed in the compressor and separated by partial condensation and distillation.
[0041] In the version of [Fig.3], the heated liquid 51 does not exist and is not returned to the liquid pumped in the pump P. If a valve is illustrated in this figure, it may exist, for example to equalize the pressures between the liquid pressurized by the pump P and the flow 29A.
[0042] Indeed, in this specific case, sending all the flow coming from the first heat exchanger El to the reboiling of column K would have increased the quantity of CO2 recycled to the compressor and therefore the latter's energy consumption.
[0043] 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 having a dew point temperature between 0 and 15°C at a first pressure containing carbon dioxide, at least one first component heavier than carbon dioxide, for example water, and at least one component lighter than carbon dioxide wherein: i. The mixture (1) is cooled to the first pressure to condense at least a portion (H) of the at least one first component it contains and form a mixture depleted in the at least one first component ii. The mixture depleted in the at least one first component is optionally dried in a dryer (D) iii. The mixture depleted in the at least one first component is optionally separated to form a stream depleted in CO2 relative to the dried mixture iv.The dried mixture or the CO2-depleted flow is cooled and then separated by partial condensation and in a distillation column (S2, S3, K) and optionally by solidification forming a CO2-enriched liquid (19) v. A portion (29) of the CO2-enriched liquid is used to cool the mixture in step i) characterized in that the portion of the CO2-enriched liquid is vaporized by indirect heat exchange with the mixture which cools in step i) forming a vaporized liquid flow and the vaporized liquid flow is sent at least in part (30) to the bottom of the column (K) in gaseous form to separate there.
2. A method according to claim 1 wherein the depleted, for example dried, mixture or the CO2-depleted flow is cooled in a second heat exchanger (E2) in which the vaporized liquid flow cools.
3. Method according to claim 1 or 2 in which the depleted mixture (3), for example dried or the flow depleted in CO2 is cooled in a heat exchanger in which the part of the liquid (29) enriched in CO2 heats up before step v).
4. A method according to one of the preceding claims 2 or 3 in which another part of the CO2-enriched liquid heats up and
5.
6.
7.
8.
9. vaporizes in the second heat exchanger (E2) and is sent to the column bottom in gaseous form for separation. Method according to one of the preceding claims 2 to 4 in which another part of the CO2-enriched liquid (35) vaporizes in the second heat exchanger (E2) and is sent to a customer without having been compressed. Method according to one of the preceding claims in which a fraction of the CO2-enriched liquid is pressurized by a pump (P) and a part of the pressurized liquid constitutes the liquid used to cool the mixture in step i). A method according to claim 6 wherein a portion of the pressurized liquid is expanded to form a liquid product (55). Method according to claim 7 in which at least a part of the vaporized flow (29A) is sent in gaseous form at a first temperature to mix with a part of the pressurized liquid intended to serve as product which is at a second temperature, lower than the first temperature. 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 (El), a second heat exchanger (E2), means for sending the mixture at the first pressure to cool in the first heat exchanger (El) 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 (El), 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, 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,
10. a portion of the vaporized liquid stream from the first heat exchanger into the bottom of the distillation column to separate therein. Apparatus according to claim 9 comprising means (P) for pressurizing a flow of CO2-rich liquid withdrawn from the bottom of the column to form a pressurized flow (55) and means for sending a portion of the vaporized liquid stream from the first heat exchanger to mix with the pressurized liquid flow.