Method for drying and liquefying co2

Abstract

A method for drying and liquefying a wet CO2 stream comprises the steps of: compressing (C1, C2) the wet CO2 stream (1) to a first pressure, compressing (C3) the CO2 stream after drying to a second pressure, expanding the CO2 stream, after cooling in a heat exchanger (E), from the second pressure in order to obtain liquid CO2 at a third pressure, drawing off a portion (11) of the liquid CO2 at the third pressure and expanding to a fourth pressure lower than the first pressure and vaporizing the portion of CO2 at the fourth pressure in the exchanger in order to generate a gaseous CO2 stream as regeneration gas. Drawing_references_to_be_translated:

Description

[0001] Description

[0002] Title of the invention: CO2 drying and liquefaction process

[0003] The present invention relates to a method for drying and liquefying CO2.

[0004] CO2 liquefiers most often include a CO2 compressor allowing the pressurization of CO2 before its cooling, liquefaction and subcooling in a unit operating at low temperature.

[0005] Subcooling in the CO2 liquefaction unit involves taking a portion of the produced liquid CO2, expanding it, and vaporizing it against the cooling CO2. The resulting gaseous CO2 is recycled upstream, in the compression stage, to complete what is commonly known as the CO2 cycle.

[0006] When the gaseous CO2 to be liquefied is moist and / or contains impurities that must be removed before liquefaction, it is typically introduced into a temperature-switching adsorption dryer to remove the water and / or impurities. STATE OF THE ART

[0007] It is typical to regenerate the dryer adsorbent with a gas emitted to the atmosphere (from the separation of impurities contained in CO2) or with a portion of the CO2 downstream of the dryer which is recycled after passing through the adsorbent upstream of the dryer to remove the water desorbed by condensation during a cooling step.

[0008] Aspelund et al., in "Gas Conditioning - The Interface Between CO2 Capture and Transport," vol. 1, no. 3, June 16, 2007, pages 343-354, describe several processes for drying and liquefying a wet CO2 stream. The regeneration gas for drying is taken from the headspace above the liquid product, which has been expanded to 4 bar (Figures 6 and 7). In this case, the gas flow rate is not necessarily sufficient for regeneration, and the expansion induces an energy loss. Alternatively, the regeneration gas is at a pressure of approximately 12 bar (Figures 2 and 3), which necessitates that the first two stages of the compressor be made of a moisture-resistant material.

[0009] PROBLEM SOLVED BY THE INVENTION

[0010] The flow rate of CO2 released into the atmosphere from a CO2 liquefier is very limited. Because the CO2 entering the system is already highly concentrated, the compounds separated within the liquefier are present in small quantities. The CO2 to be liquefied can contain between 90 and 100% mol of CO2, or even between 95 and 100% mol of CO2. This flow rate is therefore usually too low to allow for dryer regeneration, necessitating the use of an alternative fluid. The solution of using CO2 extracted downstream and recycled upstream of the dryer is energy-intensive and entails additional investment costs. Indeed, to enable this recycling, the pressure losses associated with the adsorption and regeneration loop must be compensated either by a dedicated compression stage (a fan, for example) or by recycling upstream of the compression stage preceding the dryer, thus increasing the size of this stage.In the case of a dryer receiving gas to be dried at 5 bar, for example, and therefore with an adsorption pressure of 5 bar, this implies recycling the gas used for regeneration at approximately 2.5 bar, assuming a compression ratio of 2 during the final compression stage. The only advantage of this method is regeneration at a lower pressure, thus minimizing the flow rate and regeneration energy.

[0011] According to one object of the invention, a process for drying and liquefying a wet CO2 stream is provided, comprising the following steps: a) Compression of the wet CO2 stream to a first pressure greater than 7 bar, preferably equal to at most 16 bar b) Cooling and drying of the wet CO2 stream at the first pressure in an adsorption purification unit with temperature switching in order to generate a dry CO2 stream c) Compression of the dry CO2 stream to a second pressure d) Cooling of the dry CO2 stream to the second pressure in a heat exchanger and expansion of the dry CO2 stream from the second pressure in order to obtain liquid CO2 at a third pressure e) Withdrawal of a portion of the liquid CO2 at the third pressure and expansion to a fourth pressure between 5.1 and 6 bara f) Vaporization of the portion of liquid CO2 at the fourth pressure in the heat exchanger in order to provide the necessary cooling for step d) and in order to generate a stream of gaseous CO2 at the fourth pressure as at least part of the regeneration gas g) Heating of the gaseous CO2 stream forming at least part of the regeneration gas at the fourth pressure h) Regeneration of the purification unit using at least the heated gaseous CO2 stream as regeneration gas at the fourth pressure i) Cooling of the wet regeneration gas obtained before or after mixing with the wet CO2 stream to a pressure lower than the first pressure by at least one bar j) Compression of the wet regeneration gas together with the wet CO2 stream entering from step a) and k) Production of a portion of the liquid CO2 at a pressure equal to the third pressure, higher than the third pressure or lower than the third pressure.According to other optional aspects:

[0012] • the second pressure is between 50 and 120 bara, preferably above 73 bar.

[0013] • the first pressure is greater than 10 bara, greater than 12 bara, greater than 14 bara.

[0014] • the first pressure is less than 16 bar

[0015] • Compression steps a) and c) take place in the same compressor.

[0016] • Water present in the wet CO2 stream is condensed upstream of the purification unit and removed.

[0017] • a flow of dry CO2 from an external source, for example a storage or means of transport at a pressure below the fourth pressure and compressed and mixed with the regeneration gas upstream of the purification unit.

[0018] • another part of the liquid CO2 at the third pressure, expanded from the third pressure to a pressure lower than the second pressure, or even lower than the first pressure, vaporized in the heat exchanger, the other vaporized part being mixed with the dry CO2 stream upstream of the compression of step c), without having been used as a regeneration gas.

[0019] • part of the regeneration gas consists of dry gaseous CO2 generated in a liquid CO2 storage, the storage being possibly transportable.

[0020] • The gaseous CO2 is generated at a pressure greater than 7 bar, preferably equal to at most 16 bar, preferably being generated at the fourth pressure

[0021] • another part of the liquid CO2 is taken at the third pressure and expanded from the third pressure to the first pressure, the other part expanded at the first pressure is vaporized in the heat exchanger, the other vaporized part being mixed with the dry CO2 stream upstream of the compression of step c).

[0022] • The regeneration pressure of the adsorption unit is less than 6 bar, for example between 5.1 and 6 bar

[0023] • The regeneration pressure of the adsorption unit is greater than 5.1 bara

[0024] • The regeneration pressure of the adsorption unit is between 5.1 and 6 bara

[0025] • the regeneration pressure is lower than the initial pressure

[0026] • the regeneration pressure of the adsorption unit is greater than 7 bar, preferably equal to or less than 16 bara.

[0027] • the regeneration pressure is different from the pressure at which the liquid CO2 portion is produced, for example higher than or lower than this pressure.

[0028] • Vaporization of the liquid CO2 portion at the fourth pressure in the heat exchanger provides all the cooling required for step d)

[0029] • Vaporization of the portion of liquid CO2 at the fourth pressure in the heat exchanger provides part of the cooling required for step d)

[0030] • the dry CO2 flow at the second pressure cools and liquefies in the heat exchanger (E) without having been depleted of CO2 upstream of the cooling.

[0031] • the dry CO2 flow at the second pressure cools and liquefies in the heat exchanger (E) without having been depleted in CO2 upstream of the cooling and without having been enriched in CO2 before being totally liquefied.

[0032] •

[0033] The process can be carried out in a wet CO2 stream drying and liquefaction apparatus comprising a first multi-stage compressor capable of compressing the wet CO2 stream to a first pressure greater than 7 bar, preferably equal to at most 16 bar, a cooler for cooling the stream exiting the compressor, an adsorption purification unit with temperature switching for drying the wet CO2 stream at the first pressure downstream of the cooler in order to generate a dry CO2 stream, a second compressor for compressing the dry CO2 stream to a second pressure, a heat exchanger for cooling the dry CO2 stream at the second pressure, means for expanding the dry CO2 stream downstream of the heat exchanger to expand the CO2 stream from the second pressure in order to obtain liquid CO2 at a third pressure, means for extracting a portion of the liquid CO2 at the third pressure.expansion means to reduce it to a fourth pressure lower than the first pressure, between 5.1 and 6 bara, means to send the portion of the liquid CO2 expanded in the expansion means to vaporize at the fourth pressure in the heat exchanger in order to provide the necessary cooling in step d) and to generate a flow of gaseous CO2 at the fourth pressure lower than the first pressure, means for heating the flow of gaseous CO2 to form at least a portion of the regeneration gas at the fourth pressure, means for sending the heated flow from the heating means to the purification unit as regeneration gas at the fourth pressure, a cooler for cooling wet regeneration gas obtained upstream or downstream of a mixing point of the wet regeneration gas with the wet CO2 flow,means for sending the wet regeneration gas together with the wet CO2 flow between two stages of the first compressor and means for producing a portion of the liquid CO2 as an end product at a pressure equal to, above, or below the third pressure.

[0034] DESCRIPTION OF THE INVENTION

[0035] The invention will be described in more detail with reference to the figures where: [FIG.1] represents a method according to the invention.

[0036] [FIG.2] represents a method according to the invention.

[0037] [FIG.1] represents a process according to the invention using a liquefaction apparatus comprising a three-stage compressor C1, C2, C3, a temperature-switching adsorption purification unit A (usually designated as TSA) and a heat exchanger E, for example of the brazed aluminum plate and fin type.

[0038] A wet CO2 flow 1 containing between 90 and 100 mol% CO2 is compressed in the first stage C1 of a multistage compressor and cooled in a cooler R1, which produces a flow rate of 3 and condensed water W. It is then compressed in the second stage C2 of the first compressor to a first pressure greater than 7 bar, or even greater than or equal to 10 bar, preferably less than 16 bar, and cooled in a cooler R2, which produces a flow rate of 5 and condensed water W. The wet flow at the first pressure is dried in an adsorber of the adsorption unit to obtain a dry CO2 flow rate. The dry CO2 flow is compressed in the stage C3 of the second compressor to a second pressure that allows for a significant increase in its density when cooled in a cooler R3 against a component such as cooling water or ambient air. This second pressure is typically between 50 and 120 bar.It can be subcritical or supercritical. The second compressor C3 can be part of the first compressor C1, C2, with stages C1, C2 and C3 being on the same axis.

[0039] The CO2 stream cooled in the cooler R3 is liquefied in the heat exchanger E by heat exchange with a CO2 cooling cycle originating from the CO2 stream itself. Thus, the liquefied CO2 7 is expanded to a third pressure lower than the second pressure and then divided into three parts 9, 11, 13. Part 13 is expanded from the third pressure to a pressure corresponding to the outlet pressure of a stage C1 or C2 of the first compressor, for example, the first pressure, vaporized in the heat exchanger E, and returned downstream of this stage to be cooled and liquefied with the stream 1. Alternatively, part 13 can be divided into several parts, each expanded to a different pressure, each vaporized in the exchanger, and returned to the compressor.The section 11, after pressure reduction in a valve from the third pressure to a fourth pressure at least one bar lower than the first pressure (the fourth pressure being between 5.1 and 6 bar), forms a gaseous portion and a liquid portion. The gaseous portion is heated and the liquid portion is vaporized in the heat exchanger E. The heated gaseous portion and the vaporized liquid portion are then remixed downstream of the exchanger E to form gaseous CO2 11. The gaseous CO2 11 from the vaporization step at the fourth pressure, heated by a heater H, serves as the regeneration stream for an adsorber in the purification unit A when it is saturated with water. The adsorbers A1 and A2 are connected in parallel and each operates in a cycle, such that while one adsorber is in a regeneration state, the other is in an adsorption state.The regeneration step is necessary to remove the water accumulated in the adsorbers and is carried out by sending a dry gas through the adsorber and exiting containing the accumulated water. The regeneration stream 11 exits the adsorber containing water. In this variant, it is cooled in a cooler R4, producing condensed water W, and then mixed with the flow 3 downstream of the cooler R3. The regeneration pressure of the adsorption unit is preferably less than 6 bara, for example, between 5.1 and 6 bara. The regeneration pressure of the adsorption unit is preferably greater than 5.1 bara. The regeneration pressure of the adsorption unit can be between 5.1 and 6 bara.

[0040] The regeneration pressure may be lower than the initial pressure.

[0041] Part 9 constitutes the liquid product of the liquefaction process and can be sent to a storage S. This part 9 of liquid CO2 can be produced as the final product at a pressure equal to the third pressure, above the third pressure or below the third pressure, for example by pumping it or by reducing it in a valve.

[0042] The regeneration pressure is preferably different from the pressure at which part 9 of the liquid CO2 is produced, for example lower by at least 1 bar than this pressure.

[0043] In the variant shown in Figure 2, the R4 cooler does not exist, and the regeneration flow is not cooled before being mixed with the flow 3 upstream of the R3 cooler. Thus, the R3 cooler is sized to cool both flows.

[0044] These arrangements allow for the regeneration of the dryer at marginal energy and investment costs and efficiently because they utilize a gas already available at a lower pressure than the adsorption phase. This gas, being necessarily recycled within the cycle compressor, is mixed with the wet gas; therefore, there is no need to add equipment related to this regeneration (in particular, no fan) or to oversize the compressor.

[0045] According to a variant of the invention, applicable in Figures 1 or 2, a portion of the regeneration gas may consist of dry gaseous CO2 B generated in a liquid CO2 storage facility, the storage facility being optionally transportable. For example, the storage facility may be a liquid CO2 transport vessel.

[0046] The dry gaseous CO2 B is generated in the storage at a pressure greater than 7 bar, greater than 8 bar, greater than 9 bar for example preferably equal to at most 16 bara, otherwise preferably being generated at the fourth pressure, i.e. between 5.1 and 6 bara, i.e. the pressure of the remaining regeneration gas 11. Thus the regeneration pressure is chosen in some cases to correspond to the pressure of the gas generated in the storage.

[0047] The pressure of a gas generated in a storage tank (known as "boil-off gas") is generally not high enough to recycle the gas in compressor C3 after dryers A1 and A2. Therefore, gas B must be recycled in the wet section of the machine, C1 and C2. Since recycling takes place in the wet section, this gas can be humidified and thus used as a regeneration gas without incurring additional recompression costs. As the regeneration gas has a composition substantially identical to that of the wet stream in both cases, its integration into the compressor is unlikely to affect the machine.

Claims

AMENDED CLAIMS received by the International Bureau on December 2, 2025 (02.12.2025) 1. A process for drying and liquefying a wet CO2 stream comprising the following steps: a) Compression (C1, C2) of the wet CO2 stream (1) to a first pressure greater than 7 bar, preferably equal to at most 16 bar. b) Cooling (R2) and drying of the wet CO2 stream at the first pressure in an adsorption scrubber (A, A1, A2) with temperature switching to generate a dry CO2 stream. c) Compression (C3) of the dry CO2 stream to a second pressure. d) Cooling and liquefaction of the dry CO2 stream at the second pressure in a heat exchanger (E) and expansion of the liquefied CO2 stream from the second pressure to obtain liquid CO2 at a third pressure. e) Withdrawal of a portion (11) of the liquid CO2 at the third pressure and expansion to a fourth pressure between 5.1 and 6 bar.f) Vaporization of the portion of liquid CO2 at the fourth pressure in the heat exchanger to provide the cooling required in step d) and to generate a stream of gaseous CO2 at the fourth pressure as at least part of the regeneration gas. g) Heating (H) of the gaseous CO2 stream forming at least part of the regeneration gas at the fourth pressure. h) Regeneration of the scrubber unit using at least the heated gaseous CO2 stream as the regeneration gas at the fourth pressure. i) Cooling (R1, R4) of the wet regeneration gas obtained before or after mixing with the wet CO2 stream (3) at a pressure at least one bar lower than the first pressure. j) Compression (C2) of the wet regeneration gas together with the wet CO2 stream entering from step a) and k) Production of a portion (9) of liquid CO2 at a pressure equal to, above, or below the third pressure.

2. A method according to claim 1 wherein the second pressure is between 50 and 120 bara, preferably above 73 bar.

3. Method according to claim 1 or 2 wherein the first pressure is greater than 10 bara and preferably less than 16 bara.

4. A method according to any one of the preceding claims in which the compression steps a) and c) take place in the same compressor (C1, C2, C3).

5. A method according to any one of the preceding claims wherein water (W) present in the wet CO2 stream is condensed upstream of the purification unit and removed.

6. A method according to any one of the preceding claims wherein another part (13) of the liquid CO2 at the third pressure, expanded from the third pressure to the first pressure, or even to a pressure lower than the first pressure, is vaporized in the heat exchanger (E), the other vaporized part being mixed with the dry CO2 stream upstream of the compression (C3) of step c), without having served as a regeneration gas.

7. A method according to any one of the preceding claims wherein a portion of the regeneration gas consists of dry gaseous CO2 (B) generated in a liquid CO2 storage, the storage being optionally transportable.

8. A method according to claim 7 wherein gaseous CO2 (B) is generated at a pressure greater than 7 bar, preferably equal to at most 16 bar, preferably being generated at the fourth pressure.

9. A method according to any one of the preceding claims wherein the regeneration pressure is different from the pressure at which part (9) of the liquid CO2 is produced.

10. A method according to any one of the preceding claims wherein the dry CO2 stream at the second pressure cools and liquefies in the heat exchanger (E) without having been depleted of CO2 upstream of the cooling.

11. A method according to any one of the preceding claims wherein the heated gaseous CO2 stream sent to the regeneration of the purification unit has substantially the same composition as the liquid CO2 produced.

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