CO2 purification process

Abstract

Title: CO2 Purification Process. Two streams containing CO2 (1F, 2F) with different purities are separated in a common distillation column (K), without having been compressed together. Single figure

Description

Title of the invention: CO2 purification process

[0001] The present invention relates to a CO2 purification process.

[0002] CO2 from cryogenic capture processes can be combined with that from non-cryogenic capture units such as amine scrubbing for example in order to be sent together into an export pipeline and / or into a CO2 liquefier.

[0003] It is then possible to compress the CO2 from the cryogenic unit at least partially in conjunction with the CO2 compression step from the non-cryogenic unit. Only drying of the CO2 from the non-cryogenic unit is required, if it contains any, as the water content in this CO2 is generally too high relative to the export and / or liquefaction requirements.

[0004] The purity of CO2 from the cryogenic unit is often much higher than that from other technologies. Specifications regarding the quality (impurity content) of CO2 for sequestration are constantly evolving and tend to become increasingly stringent.

[0005] It is known to use a regeneration gas from a cryogenic unit in a CO2 separation unit from amine washing.

[0006] WO 2022 / 152629 proposes a compression and drying of CO2 from amine washing using a fluid from the cryogenic unit as the regeneration gas for the dryer.

[0007] PROBLEM SOLVED BY THE INVENTION

[0008] The invention proposes an improvement to the process of WO 2022 / 152629 because, in that process, the CO2 from the amine wash is only dried but not purified into lighter molecules. Only dilution with CO2 from the cryogenic unit makes it possible to obtain an average purity that is not necessarily compatible with the specification for CO2 produced.

[0009] DESCRIPTION OF THE INVENTION

[0010] The invention may in some cases consist of: • Optionally, separately compress the CO2 from a non-cryogenic capture unit • Optionally, dry this CO2 separately • Cool it to temperatures that allow distillation • Inject this dried and cooled CO2 into the light distillation column of a cryogenic CO2 capture unit.

[0011] The invention may include the following variants / steps: • The heat exchanger enabling cryogenic separation can be shared with the exchanger enabling the cooling of CO2 from a non-cryogenic capture unit. • The cooled CO2 can be partially condensed, with the liquid phase being injected into the column for purification along with the liquid CO2 from the cryogenic unit. The gas phase can also be injected into the column, mixed with the column's overhead gas, recycled to another stage of the cryogenic process (upstream of partial condensation), or considered a by-product. • The pressure after compression of CO2 from a non-cryogenic capture unit may be higher than that of the distillation column. In this case, the CO2 (or its liquid and gaseous phases) is decompressed after cooling before being injected into the distillation column. • CO2 from a non-cryogenic capture unit can be injected into the distillation column at a different level than liquid CO2 from the cryogenic unit or at the same level.

[0012] This arrangement makes it possible to minimize the energy of separation of CO2 coming, for example from a non-cryogenic capture unit, by avoiding diluting it with the gas to be treated by the cryogenic unit while allowing its purification without additional equipment (common distillation column).

[0013] It also makes it possible to increase the CO2 recovery efficiency from a non-cryogenic capture unit. If it had been mixed with the gas to be treated by the cryogenic unit, CO2 losses would be incurred corresponding to the partial condensation efficiency of the cryogenic unit. In the case where the CO2 is injected directly into the distillation column, only reboiling losses are incurred, and it is often considered to recycle the overhead gas from the distillation column upstream of the cryogenic unit in order to minimize these losses.

[0014] According to one object of the invention, a CO2 purification process is provided in which: i. A first fluid comprising at least 35%v but less than 90%v in CO2 and containing at least one first impurity lighter than CO2, such as methane, carbon monoxide, dihydrogen, nitrogen, oxygen or argon, is compressed, the first compressed fluid is cooled, it is partially condensed generating a first gaseous phase depleted in CO2 and enriched in at least one first impurity and a first liquid phase enriched in CO2 and depleted in at least one first impurity and the first liquid phase is expanded. ii. A second fluid, other than the first gaseous or liquid phase or a fluid produced by separating the first gaseous or liquid phase, comprising at least 95%v in CO2 and containing at least one second lighter impurity such as methane, carbon monoxide, dihydrogen, nitrogen, oxygen or argon, is compressed; the second compressed fluid is cooled either by totally condensing it or by partially condensing the second compressed and cooled fluid, generating a second gaseous phase depleted in CO2 and enriched in at least one second impurity and a second liquid phase enriched in CO2 and depleted in at least one second impurity; and optionally the second liquid phase is expanded. iii. The first expanded liquid phase and either the second compressed, cooled and condensed fluid or the second liquid phase, possibly expanded, are injected into a distillation column generating a third gaseous phase depleted in CO2 and enriched in at least one first impurity and a third liquid phase enriched in CO2 and depleted in at least one first impurity.

[0015] According to other optional aspects of the invention: • the third gaseous phase is enriched in at least one second impurity and a third liquid phase is depleted in at least one second impurity. • the first fluid comprises a first principal impurity lighter than CO2 whose content is greater than any other impurity lighter than CO2 in the first fluid and the second fluid comprises a second principal impurity lighter than CO2 whose content is greater than any other impurity lighter than CO2 in the second fluid, the first principal impurity not having the same chemical composition as the second principal impurity. • the first fluid is a fluid other than the second gaseous or liquid phase or a fluid produced by separating the second gaseous or liquid phase. • the first and second fluids are cooled in the same heat exchanger, preferably by heat exchange with at least part of the third gaseous phase and / or at least part of the third liquid phase. • the second fluid is compressed to a pressure greater than that of the distillation column and the second fluid is expanded upstream of the column. • The first liquid phase and the second fluid or the second liquid phase are sent to different levels of the column. • the first liquid phase and the second fluid or the second liquid phase are mixed upstream of the column, possibly after expanding the fluid and / or at least one of the liquids. • the first fluid comes, preferably exclusively, from a first source and the second fluid comes, preferably exclusively, from a second source other than the first source • the second fluid comes, preferably exclusively, from at least one hydrocarbon reforming unit or at least one combustion unit or at least one partial condensation and / or distillation separation unit. • the first fluid comes, preferably exclusively, from at least one absorption unit, such as at least one amine or methanol washing unit or from at least one adsorption unit, such as a pressure-toggle adsorption unit or from at least one oxy-combustion unit. • The first fluid is compressed in a first compressor and the second fluid is compressed in a second compressor, the two compressors preferably being driven by different means • The first fluid is compressed by the first compressor to a higher pressure than that to which the second fluid is compressed by the second compressor • The first liquid phase is sent to the column at a level above the level to which the second condensed fluid or second liquid phase is sent. • The first fluid is compressed to a pressure between 8 and 12 bar abs • the second fluid is compressed to a pressure between 8 and 25 bars abs • the column operates at between 8 and 12 bars abs.

[0016] The invention will be described in more detail by referring to [Fig. 1].

[0017] [Fig.1] illustrates a method according to the invention.

[0018] A first source 1 produces a first fluid 1F comprising at least 35%v but less than 90%v of CO2. The first source 1 may be at least one absorption unit, such as an amine or methanol scrubbing unit, and / or at least one adsorption unit, such as a pressure-switching adsorption unit, and / or at least one oxy-combustion unit. Preferably, the first fluid 1F originates exclusively from the first source 1.

[0019] The first fluid 1F contains at least one first impurity lighter than CO2, such as methane, carbon monoxide, dihydrogen, nitrogen, oxygen or argon. The principal impurity lighter than CO2, the content of which is higher than the other impurity(ies) lighter than CO2, may be methane, carbon monoxide, dihydrogen, nitrogen, oxygen, or argon. The first fluid 1F is compressed in a first compressor IC, optionally dried in a first dryer, then the first compressed fluid is cooled first by a cooler IR and then in a heat exchanger E where the first fluid 1F partially condenses, generating a first gaseous phase IG depleted in CO2 and enriched in at least one first impurity, and a first liquid phase IL enriched in CO2 and depleted in at least one first impurity in a phase separator 1S. The first liquid phase IL is expanded in a valve IV and sent to the top of a distillation column K.

[0020] The first source 1 can be from a hydrocarbon reforming unit or a combustion unit. Preferably, the first fluid comes exclusively from the first source 1.

[0021] A second source 2 produces a second fluid 2F comprising at least 95%v of CO2. The second source is preferably at least one hydrocarbon reforming unit and / or at least one combustion unit and / or at least one partial condensation and / or distillation separation unit.

[0022] The second fluid 2F contains at least one other impurity lighter than CO2, such as methane, carbon monoxide, dihydrogen, nitrogen, oxygen, or argon. The principal impurity lighter than CO2, the content of which is higher than the other impurity(ies) lighter than CO2, may be methane, carbon monoxide, dihydrogen, nitrogen, oxygen, or argon. The second fluid 2F is compressed in a second compressor 2C, optionally dried in a second dryer, then the second compressed fluid is cooled first by a cooler 2R and then in a heat exchanger E where the second fluid 2F partially condenses generating a second gaseous phase 2G depleted in CO2 and enriched in at least one other impurity and a second liquid phase 2L enriched in CO2 and depleted in at least one other impurity in a phase separator 2S.The first liquid phase 2L is expanded in a 2V valve and sent to a distillation column K at a level below the injection level of liquid IL.

[0023] Otherwise the 2L liquid can be sent to a level above the IL liquid injection level.

[0024] The partial condensation step of the second fluid is not essential. The second fluid 2F can be sent to column K in gaseous or liquid form, having been liquefied in the heat exchanger E.

[0025] According to one embodiment, the second fluid can thus be completely condensed, either at the column pressure or at a pressure higher than that of the column, in which case it is expanded upstream of the column. The second condensed fluid is then sent to the distillation column to be separated at a level below the injection level of liquid IL.

[0026] The second fluid can at most be partially condensed at a lower pressure than that at which the first fluid is partially condensed, since it contains more CO2.

[0027] The distillation column K generates a third gaseous phase 3G depleted in CO2 and enriched in at least one first impurity at the top of the column, and a third liquid phase enriched in CO2 and depleted in at least one first impurity. The third liquid phase is divided into two flows, one 3L of which is vaporized in the heat exchanger E at the pressure of column K, and another 3L' is expanded through a valve 3V in the heat exchanger E at a pressure lower than that of column K. A portion of the vaporized 3L' flow is returned to the hot end of the heat exchanger E in the tank of column K.

[0028] The 3G gas is heated in the heat exchanger E or can otherwise be sent to the air without being heated.

[0029] It will be understood in this document that cryogenic temperatures can reach up to -40°C.

Claims

Demands

1. A CO2 purification process in which: i. A first fluid (1F) comprising at least 35%v but less than 90%v in CO2 and containing at least one first impurity lighter than CO2, such as methane, carbon monoxide, dihydrogen, nitrogen, oxygen or argon, is compressed, the first compressed fluid is cooled, it is partially condensed generating a first gaseous phase (IG) depleted in CO2 and enriched in at least one first impurity and a first liquid phase (IL) enriched in CO2 and depleted in at least one first impurity and the first liquid phase is expanded. ii. A second fluid (2F), other than the first gaseous or liquid phase or a fluid produced by separating the first gaseous or liquid phase, comprising at least 95%v in CO2 and containing at least one second lighter impurity such as methane, carbon monoxide, dihydrogen, nitrogen, oxygen or argon, is compressed and cooled either by totally condensing it or by partially condensing the second compressed and cooled fluid generating a second gaseous phase (2G) depleted in CO2 and enriched in at least one second impurity and a second liquid phase (2L) enriched in CO2 and depleted in at least one second impurity and optionally the second liquid phase is expanded. iii. The first expanded liquid phase and either the second compressed, cooled and condensed fluid or the second liquid phase, possibly expanded, are injected into a distillation column (K) generating a third gaseous phase (3G) depleted in CO2 and enriched in at least one first impurity and a third liquid phase (3L, 3L') enriched in CO2 and depleted in at least one first impurity.

2. A process according to claim 1 wherein the third gaseous phase (3G) is enriched in at least one second impurity and a third liquid phase (3L, 3L') is depleted in at least one second impurity.

3. A process according to claim 1 or 2 wherein the first fluid (1F) comprises a first principal impurity lighter than CO2 having a content greater than any other impurity lighter than CO2 of the first fluid and the second fluid (2F) comprises a second principal impurity lighter than CO2 having a content greater than any other impurity lighter than CO2 of the second fluid, the first principal impurity not having the same chemical composition as the second principal impurity.

4. A method according to any one of the preceding claims wherein the first fluid (1F) is a fluid other than the second gaseous (2G) or liquid (2L) phase or a fluid produced by separating the second gaseous or liquid phase.

5. A method according to any one of the preceding claims wherein the first and second fluids (1F, 2F) are cooled in the same heat exchanger, preferably by heat exchange with at least a portion of the third gaseous phase (3G) and / or at least a portion of the third liquid phase (3L, 3L').

6. A method according to any one of the preceding claims wherein the second fluid (2F) is compressed to a pressure greater than that of the distillation column and the second fluid is expanded upstream of the column.

7. A method according to any one of the preceding claims in which the first liquid phase (IL) and the second fluid (2F) or the second liquid phase (2L) are sent to different levels of the column.

8. A method according to any one of the preceding claims 1 to 6 in which the first liquid phase (IL) and the second fluid (2F) or the second liquid phase (2L) are mixed upstream of the column, optionally after expanding the fluid and / or at least one of the liquids.

9. A process according to any one of the preceding claims wherein the second fluid (2F) is preferably derived exclusively from at least one hydrocarbon reforming unit or at least one combustion unit or at least one partial condensation and / or distillation separation unit.

10. A process according to any one of the preceding claims wherein the first fluid (1F) is obtained, preferably exclusively, from at least one absorption unit, such as an amine or methanol washing unit, or from at least one adsorption unit, such as a pressure-toggle adsorption unit, or from at least one oxy-combustion unit.

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