Process and apparatus for drying and liquefying CO2

Abstract

Title of the invention: Process and apparatus for drying and liquefying a wet CO2 stream. A process for drying and liquefying a wet CO2 stream comprising the steps: compression (C1, C2) of the wet CO2 stream (1) to a first pressure greater than 7 bar, drying of the wet CO2 stream at the first pressure in a purification unit (A) to generate a dry CO2 stream, compression (C3) of the dry CO2 stream to a second pressure, cooling of the dry CO2 stream at the second pressure in a heat exchanger (E) and expansion of the dry CO2 stream from the second pressure to obtain liquid CO2 at a third pressure.a portion (11) of the liquid CO2 is extracted at the third pressure and expanded to a fourth pressure lower than the first pressure, and the portion of liquid CO2 at the fourth pressure is vaporized in the heat exchanger to generate a flow of gaseous CO2 at the fourth pressure lower than the first pressure as the regeneration gas for the purification unit. FIG.1,

Description

Title of the invention: Method and apparatus for drying and liquefying CO2

[0001] The present invention relates to a method and apparatus for drying and liquefying CO2.

[0002] 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.

[0003] Subcooling in the CO2 liquefaction unit consists of taking a portion of the liquid CO2 produced, 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 called the CO2 cycle.

[0004] When the gaseous CO2 to be liquefied is wet and / or contains impurities to be removed before liquefaction, it is typically introduced into a temperature-toggle type adsorption dryer to remove the water and / or impurities.

[0005] STATE OF THE ART

[0006] 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.

[0007] PROBLEM SOLVED BY THE INVENTION

[0008] The flow rate of CO2 released into the atmosphere from a CO2 liquefier is very limited. This is because the CO2 entering the system is already highly concentrated, resulting in small quantities of the compounds separated within the liquefier. 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, making it necessary to use another fluid. The solution of using CO2 extracted downstream and recycled upstream of the dryer is energy-intensive and entails additional investment costs.

[0009] Indeed, in order to enable this recycling, the pressure losses related to the adsorption and then 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 bara, for example, and therefore with an adsorption pressure of 5 bara, this implies recycling the gas used for regeneration at approximately 2.5 bara in the case of a compression ratio of 2 during the last compression stage. The only advantage of this method is regeneration at lower pressure, allowing for minimization of the flow rate and regeneration energy.

[0010] According to one object of the invention, a process for drying and liquefying a wet CO2 stream is provided, comprising the following steps:

[0011] a) Compression of the wet CO2 flow to a first pressure greater than 7 bar, preferably equal to at most 16 bar

[0012] b) Cooling and drying the wet CO2 stream at first pressure in an adsorption purification unit with temperature switching in order to generate a dry CO2 stream

[0013] c) Compression of the dry CO2 flux to a second pressure

[0014] d) Cooling of the dry CO2 stream at the second pressure in a heat exchanger heat and expansion of the dry CO2 flow from the second pressure in order to obtain liquid CO2 at a third pressure

[0015] e) Taking a portion (of the liquid CO2 at the third pressure and reducing it to a fourth pressure lower than the first pressure, preferably between 5.1 and 6 bar

[0016] f) Vaporization of the portion of liquid CO2 at the fourth pressure in the heat exchanger in order to provide the cooling required in step d) and in order to generate a flow of gaseous CO2 at the fourth pressure lower than the first pressure as at least a portion of the regeneration gas

[0017] g) Heating of the gaseous CO2 stream forming at least a part of the regeneration gas at the fourth pressure

[0018] h) Regeneration of the purification unit using at least the heated gaseous CO2 stream as the regeneration gas at the fourth pressure

[0019] i) Cooling of the wet regeneration gas obtained before or after mixing with the wet CO2 stream to a pressure at least one bar lower than the first pressure

[0020] j) Compression of the wet regeneration gas jointly with the wet CO2 flow entering from step a)

[0021] and

[0022] k) Production of a portion of the liquid CO2 at a pressure equal to the third pressure, greater than the third pressure or less than the third pressure.

[0023] According to other optional aspects: • the second pressure is between 50 and 120 bara, preferably above 73 bar. • the first pressure is greater than 10 bara, greater than 12 bara, greater than 14 bara. • the first pressure is less than 16 bar • Compression steps a) and c) take place in the same compressor. • water present in the humid CO2 stream is condensed upstream of the purification unit and removed. • 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. • 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. • part of the regeneration gas consists of dry gaseous CO2 generated in a liquid CO2 storage, the storage being possibly transportable. • 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 • 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). • The fourth pressure is less than 6 bara, for example between 5.1 and 6 bara. • The regeneration pressure of the adsorption unit is less than 6 bara, for example between 5.1 and 6 bara. • the fourth pressure is greater than 7 bar, preferably equal to or less than 16 bar • the regeneration pressure of the adsorption unit is greater than 7 bar, preferably equal to or less than 16 bara.

[0024] According to another aspect of the invention, a device for drying and liquefying a wet CO2 stream is provided, 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 to 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, and a heat exchanger. heat to cool 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 to obtain liquid CO2 at a third pressure, means for taking a portion of the liquid CO2 at the third pressure, means for expanding it to a fourth pressure lower than the first pressure, preferably between 5.1 and 6 bara, means for sending the portion of the expanded liquid CO2 in the expansion means to vaporize at the fourth pressure in the heat exchanger to provide the necessary cooling in step d) and to generate a gaseous CO2 stream at the fourth pressure lower than the first pressure, means for heating the gaseous CO2 stream 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 liquid CO2 as an end product at a pressure equal to, above, or below the third pressure.

[0025] DESCRIPTION OF THE INVENTION

[0026] The invention will be described in more detail with reference to the figures where:

[0027] [Fig.1] represents a method according to the invention.

[0028] [Fig.2] represents a method according to the invention.

[0029] [Fig. 1] represents a process according to the invention using a liquefaction apparatus including a three-stage compressor Cl, C2, C3, a temperature-switching adsorption purification unit A (usually designated as TSA) and a heat exchanger E, for example of the brazed aluminium plate and fin type.

[0030] A wet CO2 flow 1 containing between 90 and 100 mol% CO2 is compressed in the first stage C1 of a first multistage compressor and cooled in a cooler R1, forming 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 1 bar, preferably less than 16 bar, and cooled in a cooler R2, forming 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 allowing a significant increase in its density upon cooling in a cooler R3 against a component such as cooling water or air. Ambient, for example. 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 Cl, C2, with stages Cl, C2, and C3 on the same axis.

[0031] 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 being vaporized in the exchanger and returned to the compressor.The portion 11, after pressure reduction in a valve from the third pressure to a fourth pressure at least one bar lower than the first pressure, preferably less than 6 bar, for example 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 of 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, so that while one adsorber is in a regeneration state, the other adsorber 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 flow 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.

[0032] Part 9 constitutes the liquid product of the liquefaction process and can be sent to a storage S. This part 9 of the 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 depressurizing it in a valve.

[0033] In the variant of [Fig.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 flow rates.

[0034] These arrangements allow the dryer to be regenerated at marginal energy and investment cost and efficiently because they use 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, it is not necessary to add equipment related to this regeneration (in particular, no fan) or to oversize the compressor.

[0035] 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 tank, the storage tank being optionally transportable. For example, the storage tank may be a tank in a liquid CO2 transport vessel.

[0036] 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 bar, preferably being generated at the fourth pressure, that is to say the pressure of the remaining regeneration gas 11. Thus the regeneration pressure is chosen to correspond to the pressure of the gas generated in the storage.

[0037] The pressure of a gas generated in a storage tank (in English, "boil-off gas") is generally not high enough to recycle the gases in the compressor C3 after the dryers A1, A2. Therefore, gas B must be recycled in the wet section of the machine C1, C2. Since recycling takes place in the wet section, it is possible to humidify this gas: it can therefore be used as a regeneration gas without incurring additional recompression costs.

Claims

1. Demands A process for drying and liquefying a wet CO2 stream comprising the following steps: a) Compression (Cl, C2) of the wet CO2 flux (1) up to a first pressure greater than 7 bar, preferably equal to at most 16 bara. b) Cooling (R2) and drying of the wet CO2 stream at the first pressure in an adsorption purification unit (A, Al, A2) with temperature switching to generate a dry CO2 stream. c) Compression (C3) of the dry CO2 stream to a second pressure. d) Cooling of the dry CO2 stream at the second pressure in a heat exchanger (E) and expansion of the dry CO2 stream from the second pressure to obtain liquid CO2 at a third pressure. e) Taking a portion (11) of the liquid CO2 at the third pressure and reducing it to a fourth pressure lower than the first pressure, preferably 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 in step d) and in order to generate a flow of gaseous CO2 at the fourth pressure lower than the first 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 purification unit using at least the heated gaseous CO2 stream as regeneration gas at the fourth pressure. i) Cooling (RI, R4) of the wet regeneration gas obtained before or after mixing with the wet CO2 stream (3) at a pressure lower than the first pressure by at least one bar. j) Compression (C2) of the wet regeneration gas together with the wet CO2 stream entering from step a) and k) Production of a part (9) of the liquid CO2 at a pressure equal to the third pressure, above the third pressure 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. A 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 wherein the compression steps a) and c) take place in the same compressor (Cl, 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, 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. Apparatus for drying and liquefying a wet CO2 stream comprising a multi-stage compressor (Cl, C2) capable of compressing the wet CO2 stream (1) to a first pressure greater than 7 bar, preferably equal to at most 16 bar, a cooler (R2) for cooling the stream exiting the first compressor, an adsorption scrubber unit (A, Al, A2) 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 (C3) for compressing the dry CO2 stream to a second pressure, a heat exchanger (E) 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 to obtain liquid CO2 at a third pressure, means for taking a portion (11) of the liquid CO2 at the third pressure, means for reducing it to a fourth pressure lower than the first pressure, preferably between 5.1 and 6 bara, means for sending the portion of the liquid CO2 reduced in the means for vaporizing at the fourth pressure in the heat exchanger in order to provide the cooling required in step d) and in order to generate a flow of gaseous CO2 at the fourth pressure lower than the first pressure, means for heating (H) 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 scrubber unit as regeneration gas at the fourth pressure, a chiller (RI,R4) for cooling wet regeneration gas obtained upstream or downstream of a mixing point of the wet regeneration gas with the wet CO2 stream (3), means for sending the wet regeneration gas together with the wet CO2 stream between two stages of the first compressor and means for producing a portion (9) of the liquid CO2 as an end product at a pressure equal to, above, or below the third pressure.

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