CO2 capture method and apparatus

Abstract

Title of the invention: Method and apparatus for capturing CO2 In a method for separating a gas mixture containing CO2 and at least one component, the gas mixture is separated by adsorption generating a fluid (1) enriched in CO2 and depleted in the at least one component relative to the gas mixture and a gas enriched in the at least one component and depleted in CO2 relative to the gas mixture under a pressure greater than 6 bara, the CO2-enriched fluid is separated in a separation unit and a portion of the CO2-depleted fluid is used as a barrier gas for a compressor (C1, C2, C3, C4, C5, C6, C7) of the separation unit. Abstract figure: Fig 3

Description

Title of the invention: Method and apparatus for capturing CO2

[0001] Introduction

[0002] The present invention relates to a method and apparatus for capturing CO2. The present invention relates in particular to a method and apparatus for separating by partial condensation and / or distillation and / or solidification a gas containing CO2 to produce a CO2-rich fluid. The mixture to be separated contains CO2 and at least one component lighter than CO2, such as carbon monoxide, hydrogen, nitrogen, oxygen, methane and optionally at least one component heavier than CO2, such as NOx.

[0003] On the other hand, it is also relative to other CO2 capture technologies, for example absorption.

[0004] In particular, the method can treat a gas resulting from combustion, for example an oxycombustion process, to form a product rich in CO2, for example containing at least 80 mol% of CO2, or even at least 90 mol% of CO2.

[0005] Low temperature separation operates at temperatures below 0°C, or even below -40°C.

[0006] The processes for capturing CO2 from low-content flue gases by a so-called cryogenic route may comprise a step of pre-concentrating the flue gases. This step consists of a pressure swing adsorption or PSA process or a membrane separation process which generates a CO2-enriched fluid at a first pressure (known in English as "PSA tail gas" for the PSA or permeate of the membrane separation) and a CO2-depleted fluid at a second pressure higher than the first pressure (pressure gas of the PSA or retentate of the membrane separation) expanded and emitted to the atmosphere.

[0007] Such a process with a PSA separation upstream of a low temperature separation is known from FR2872890A1.

[0008] The CO2-enriched fluid can be compressed in a compressor and then separated at a temperature below -30°C by partial condensation and / or distillation and / or washing and / or solidification producing a CO2-rich fluid and a CO2-depleted fluid, one and / or the other of these fluids being able to be compressed also in a dedicated compressor.

[0009] Alternatively, the CO2-enriched fluid may be compressed in a compressor and then separated by absorption as described in “Design of the CO2 Removal Section for PSA Tail Gas Treatment in a Hydrogen Production Plant” by Pellegrini et al, Front. Energy Res. May 2020.

[0010] Rotating machines require the use of seal gas to prevent gas leaks and ensure their tightness. However, using nitrogen as a seal gas can be expensive because it often requires a nitrogen generation unit.

[0011] Separation devices include many automatic valves that allow the regulation of operating parameters such as flow rate, pressure, level. The goal is to obtain the right specifications such as production flow rate, product purity.

[0012] These automatic valves are equipped with electro-pneumatic positioners that allow the valve's opening position to be adjusted. The positioner receives a signal that specifies the valve's opening percentage. Instrumentation air arrives at the positioner, which will send air into the diaphragm of a valve to open a valve closed due to lack of air. Conversely, the positioner will open a vent to close the valve.

[0013] These instrumentation valves generally require instrumentation air generated via a dry air generation unit.

[0014] The adsorption or membrane separation step generates a high-pressure CO2-depleted fluid (PSA nitrogen waste or membrane retentate) which is expanded and emitted to the atmosphere. The CO2-depleted fluid is under pressure, dry, and rich in nitrogen.

[0015] Other cryogenic CO2 capture processes are supplemented by a step of separating the incondensables. Similarly, this step consists of a PSA or a membrane, the low-pressure fluid enriched in CO2 being recycled upstream of the cryogenic step and the high-pressure fluid enriched in nitrogen being expanded and emitted to the atmosphere.

[0016] The present invention proposes to use at least part of the nitrogen-enriched and CO2-depleted gas produced by the adsorption separation or membrane separation unit as barrier gas and / or as instrumentation gas, leading to a reduction in capture costs and to an optimization of utility management.

[0017] State of the art

[0018] In industry, there are several common configurations for barrier gases used in machinery and compressors. One of the most common configurations is the use of nitrogen to prevent gas leaks and to provide sealing at rotating shafts in machinery and compressors. Another possibility is the use of another dry barrier gas, such as instrument air, which may be less expensive and more readily available on site (this can be problematic at times as it may contain particles and contaminants).

[0019] The most common configurations for barrier systems are carbon ring seals, labyrinth seals and dry gas seals. Each of these configurations has its own advantages and disadvantages, and the choice of the appropriate configuration depends on the application specifications and operational requirements (expensive or hazardous gases involved, any constraints between the process and barrier gas, production pressure, etc.) and of course the investment cost aspects.

[0020] Problem solved by the invention

[0021] The NS (nitrogen service) is considered a utility. It is not always available (for example, in the case of capture at cement plants, lime production plants, metal production industry among others) and even if it is available, intrinsic costs are added to the cost of capture (for example, the redevelopment of the NS network due to the increase in capacity). When the NS is not available, it can be provided by a nitrogen generation unit such as an air separation device by cryogenic distillation or by permeation. This entails additional investment costs and operating costs (electricity and cooling water) and can even be very restrictive in the case of unavailability or limitation of the space dedicated to a new capture unit. The same is true for the generation of purified air for instrumentation.

[0022] Description of the invention

[0023] The nitrogen-enriched, CO2-depleted gas from a PSA on flue gases (in English "fine gas") is a dry gas rich in nitrogen N2 (85 to 95% mol), under pressure (10 to 6 bara) and at a temperature close to ambient temperature. These conditions are generally those at which nitrogen service (NS) is required. The use of at least part of the latter as a barrier gas could offer savings compared to a dedicated unit as mentioned above.

[0024] The use of nitrogen-enriched, CO2-depleted gas will have a very small effect in terms of operating costs, due to a slight decrease in the energy recovered by the nitrogen-enriched, CO2-depleted gas expansion turbines under pressure (often intended to expand the gas to recover energy). No adverse effect is identified on the process flowsheet. This effect is also limited because the fraction used is very small. On the other hand, the elimination of a nitrogen generation unit (air separation device by cryogenic distillation or a membrane separation or others) drastically reduces the electricity consumption, the associated cooling water consumption, as well as the space requirement.

[0025] The proposed configuration consists of replacing the nitrogen often used as a barrier gas with a CO2-depleted, N2-rich fluid at high pressure at the outlet of a PSA on fumes (in English "fine gas") or a residue from membrane separation. In this configuration, it is sufficient to connect to the collector of the pressurized product of the PSA, using a tapping to distribute the dry gas to the barrier system of the various machines of the capture unit and / or the instrumentation gas network. The same approach can also be planned on the residue of a membrane separation unit, replacing the PSA, to obtain a gas that is also dry, under pressure and rich in nitrogen.

[0026] This configuration includes the possibility that liquid nitrogen with a vaporizer for producing pressurized nitrogen gas and / or pressurized CO2 can be used as backup to the barrier gas and the gas network for the instrumentation by connecting them to the same network.

[0027] In normal operation, this integration does not impose blocking constraints on the system. The main issue linked to the use of this gas enriched in nitrogen and depleted in CO2 is its purity and in particular its oxygen content and possible impurities of the order of a few ppm to hundreds of ppm of NOx for example.

[0028] Indeed, in certain applications, the specification of the final product requires compliance with certain impurity levels. In the event of leaks of the barrier gas into the process, these impurities could therefore contaminate the final product and / or lead to an adaptation of the sizing of the equipment downstream of these machines. In this case, it would be preferable to use a barrier system involving the leakage of the process gas into the barrier gas and not the other way around.

[0029] In the event that the nitrogen-enriched and CO2-depleted gas is unavailable (start-up, PSA or membrane triggering, shutdown, etc.), a backup gas will be necessary. It may come from CO2 production and / or from the vaporization of a stored cryogenic liquid (e.g. liquid nitrogen).

[0030] The advantages of this configuration are therefore as follows: • The ability to supply its own barrier gas for sealing machines (optimization using the residual gas enriched in nitrogen and depleted in CO2 as a usable by-product), and / or its instrumentation gas. • Reduction of investment and / or operating costs by eliminating the need for a nitrogen and / or dry air generation unit. • Compact solution minimizing additional space.

[0031] According to an object of the invention, there is provided a method for separating a gas mixture containing CO2 as well as at least one component which is nitrogen and / or oxygen and / or argon comprising the steps of i. the separation of the pressurized gas mixture during an adsorption and / or membrane permeation step generating a fluid enriched in CO2 and depleted in at least one component relative to the gas mixture and a gas enriched in at least one component and depleted in CO2 relative to the gas mixture under a pressure greater than 6 bara ii. cooling the CO2-enriched fluid producing a cooled CO2-enriched fluid iii. a) separating the cooled CO2-enriched fluid from step ii) by partial condensation and / or distillation and / or solidification to produce at least one CO2-rich fluid and at least one CO2-lean fluid comprising a step of compressing in a compressor the CO2-enriched fluid, before or after the cooling of step ii) or a fluid produced by the low-temperature separation or a refrigeration cycle and / or expanding in a turbine a fluid produced by the low-temperature separation and / or pressurizing in a pump a liquid produced by the low-temperature separation and / or a step of regulating by a pneumatic regulating valve a fluid used, to be separated or separated in the low-temperature separation and / or

[0032] b) separating the cooled CO2-enriched fluid from step ii) by absorption comprising a step of compressing in a compressor the CO2-enriched fluid or a fluid produced by the absorption separation and a step of separating by absorption the CO2-enriched fluid by absorption

[0033] characterized by the use of at least a portion of the gas enriched in the at least one component as a barrier gas for the compressor and / or the turbine and / or the pump and / or as an instrumentation gas for the pneumatic valve.

[0034] According to other optional features: • the compressor barrier system induces a leak of the barrier gas into the compressed fluid in the compressor or the turbine barrier system induces a leak of the barrier gas into the expanded fluid in the turbine • a barrier system of at least one turbine, compressor or pump downstream of the separation stage induces a leak of the compressed gas in the compressor or expanded in the turbine towards the barrier gas. • the process comprises sending the barrier gas and possibly the compressed or expanded gas having leaked towards the barrier gas after passing through at least one rotating machine upstream of the separation step. • the gas enriched in at least one component used as barrier and / or instrumentation gas is replaced when it is unavailable by vaporized nitrogen from a liquid nitrogen storage. • the gas enriched in at least one component used as barrier and / or instrumentation gas is replaced when it is unavailable by vaporized CO2 from liquid storage or a fluid from the CO2-enriched fluid.

[0035] According to another object of the invention, there is provided an apparatus for separating a gas mixture containing CO2 as well as at least one component which is nitrogen and / or oxygen and / or argon comprising a membrane adsorption and / or permeation separation unit, means for sending the pressurized gas mixture into the membrane adsorption and / or permeation unit to be separated, generating a fluid enriched in CO2 and depleted in the at least one component relative to the gas mixture and a gas enriched in the at least one component and depleted in CO2 relative to the gas mixture under a pressure greater than 6 bara, means for cooling the CO2-enriched fluid producing a cooled CO2-enriched fluid,a separation unit by partial condensation and / or distillation and / or solidification, means for sending cooled CO2-enriched fluid from step ii) by partial condensation and / or distillation and / or solidification to produce at least one CO2-rich fluid and at least one CO2-poor fluid, the separation unit comprising a compressor for compressing CO2-enriched fluid, before or after cooling in the cooling means or a fluid produced by the low-temperature separation or a fluid from a refrigeration cycle and / or comprising a turbine for expanding a fluid produced by the low-temperature separation and / or a pump for pressurizing a liquid produced by the low-temperature separation and / or a pneumatic control valve for regulating a fluid used,to be separated or separated in the low temperature separation characterized in that it comprises means for sending at least a portion of the gas enriched in the at least one component as a barrier gas for the compressor and / or the turbine and / or the pump and / or as an instrumentation gas for the pneumatic valve.

[0036] According to another object of the invention, there is provided an apparatus for separating a gas mixture containing CO2 as well as at least one component which is nitrogen and / or oxygen and / or argon comprising a unit for separation by adsorption and / or membrane permeation, means for sending the pressurized gas mixture into the unit for adsorption and / or membrane permeation to be separated, generating a fluid enriched in CO2 and depleted in the at least one component relative to the gas mixture and a gas enriched in the at least one component and depleted in CO2 relative to the gas mixture under a pressure greater than 6 bara, means for cooling the CO2-enriched fluid producing a cooled CO2-enriched fluid, an absorption separation unit, means for sending cooled CO2-enriched fluid to be separated by absorption,the separation unit comprising a compressor of the CO2-enriched fluid or of a fluid produced by absorption separation and, an apparatus for separation by absorption of the fluid enriched in CO2 by absorption characterized in that it comprises means for sending at least a portion of the gas enriched in the at least one component as a barrier gas for the compressor.

[0037] The invention will be described in more detail with reference to the figures:

[0038] [Fig-1] schematically represents the upstream part of a process according to the invention.

[0039] [Fig.2] schematically represents a variant of the upstream part of a process according to the invention.

[0040] [Fig.3] schematically represents the downstream part of a method according to the invention.

[0041] [Fig. 1] shows a CO2 pressure rocking adsorption separation unit PSA used to separate a MG gas mixture, possibly dried upstream for example by TSA (temperature swing adsorption). The separation produces a flow 1 enriched in CO2 and depleted in nitrogen compared to the MG gas mixture and a NW flow under a pressure greater than 6 bars enriched in nitrogen and depleted in CO2 compared to the MG gas mixture.

[0042] The gas mixture MG may come from combustion, a cement plant, a steel mill or another source of a gas containing CO2 and nitrogen.

[0043] The NW flow can be expanded in a turbine to produce energy. At least a portion of the NM flow is used as instrumentation gas IG and / or at least a portion of the NM flow is used as barrier gas SGI, SG2, SG2 in a rotating machine of a process downstream of the PSA separation.

[0044] In [Fig.2], the CO2 PSA adsorption separation unit is replaced by a membrane separation unit M whose permeate is gas 1 and whose residue is gas NW, IG, SGI, SG2, SG3.

[0045] [Fig.3] schematically represents a process using a single column of distillation to remove a component lighter than CO2 in a first column.

[0046] The gas flow rate corresponds to flow rate 1 produced by the adsorption unit of [Fig. 1] or the permeation separation unit of [Fig. 2]. This flow rate is enriched in CO2 and depleted in nitrogen compared to the gas mixture MG. The gas mixture MG contains CO2 as well as at least one component which is nitrogen and / or oxygen and / or argon.

[0047] A gas flow 1 is compressed in a multi-stage compressor, here four stages C1, C2, C3, C4, here with a cooler R1, R2, R3 between each stage and two coolers R4, R5 downstream of the last stage. This flow 1 can for example be the residual of a PSA H2 or CO2 and can be compressed to at least 35 bar abs in the compressor stages C1 to C4. The coolers R1 to R3 are cooled only by cooling water CW, as is the cooler R5.

[0048] The gas flow 1 contains CO2 and at least one lighter component which may be hydrogen, carbon monoxide, nitrogen or oxygen. In this example, the gas flow is rich in nitrogen. Preferably the gas flow 1 contains less than 1 mol% of methane.

[0049] The gas flow cooled in the two coolers R4, R5 downstream of the last stage is cooled to a temperature below -50°C in a first heat exchanger E by heat exchange with at least one fluid from the cold separation. This exchanger E may be of the brazed aluminum plate and fin type.

[0050] The gas flow 1 partially condenses in the first heat exchanger E and the two-phase flow formed is separated in a phase separator S forming a gas 3 enriched in at least one lighter component, here at least nitrogen. This gas heats up in the first exchanger E and then heats up in the first cooler R4 directly following the last stage C4 of the compressor from a temperature of 30°C to a temperature of 100°C, being the only cooling fluid sent to this first cooler R4. Then the gas cooled in the first cooler R4 cools down in a second cooler R5 against cooling water CW at an ambient temperature below 40°C, or even below 30°C.

[0051] Alternatively, the gas flow 3 enriched with the at least one light component can cool the compressed gas in the second cooler R5, the first being cooled by water.

[0052] Alternatively or in addition, the flow enriched in the at least one light component can cool the compressed gas in a cooler RI, R2, R3 between two stages of the compressor.

[0053] Thus the gas 3 to be expanded in a turbine T is preheated against the compressed gas in the compressor C1 to C4, so that the compression heat makes it possible to produce more energy in the turbine.

[0054] The gas flow 3 enriched with light component heated in the first cooler R4 is at 8 bar and is expanded in the turbine T from this pressure to approximately atmospheric pressure. The gas flow enriched with light component 3 can then be used to regenerate adsorbents to dry the gas feeding the PSA to produce flow 1.

[0055] The liquid 5 from the phase separator S is sent to the top of a distillation column C from which a liquid 9 enriched in CO2 and depleted in the at least one light component is withdrawn in the bottom. This liquid can form at least part of the product of the process. At least part of the liquid is pressurized by a pump P and can be sent to vaporize in the first heat exchanger E, a part 11 of the vaporized liquid possibly being sent to the bottom of the column C as reboiling. At least a portion 13 of the vaporized liquid may be compressed in a product compressor C5 driven by turbine T to produce a CO2-rich gas. The gas is then compressed by further compression stages C6, C7, with a water cooler CW between each pair of stages (R6 between C5 and C6) and a final cooler downstream of stage C7. The gas compressed in C7 constitutes the CO2-rich product gas in this example.

[0056] The head gas 7 from column C is heated in the first exchanger E.

[0057] The exchanger E, the phase separator S and the column C are inside a thermally insulated CB enclosure.

[0058] Two means of cold production are used: • A closed cycle in which CO2 is compressed in a CC cycle compressor and returned to the first heat exchanger where it is cooled, liquefied, separated and expanded in two different valves to form two flows at 5.5 and 9.5 bar abs. These two flows are reheated in the first heat exchanger E to provide cold and are then returned to the CC cycle compressor. • Vaporization of liquid 9 in exchanger E.

[0059] Obviously the system can comprise several phase separators, in series and / or in parallel and upstream of the distillation as well as at least one distillation column.

[0060] If the system does not include a phase separator, the gas expanded in the turbine will be taken at the top of the distillation column.

[0061] One of the barrier gases SGI, SG2, SG3 which is a part of the NW gas is sent as barrier gas to: • at least one stage of the compressor Cl, C2, C3, C4 and / or • the turbine T and / or • the P pump and / or • at least one stage of the DC compressor and / or • at least one stage of compressor C5, C6 or C7

[0062] An instrument gas IG is sent to the various valves of the process which are not fully represented in the figure.

[0063] It will be understood that [Fig. 3] represents one example among many others possible for separating the gas flow 1 as published in FR3127556A1. A method for carrying out this separation may comprise only at least one partial condensation step, only at least one distillation step, only at least one washing step, a solidification step associated with a partial condensation and / or distillation step. Examples of methods are found for example in FR3127558A1, EP4245400A1, US20233221067.

[0064] It is also possible to separate the CO2-enriched fluid 1 by absorption, as described in the Pellegrini article. In this case, the CO2-depleted, nitrogen-enriched gas is sent as a barrier gas to a compressor of the fluid 1 upstream of the absorption or of a gas produced by absorption.

Claims

1. Claims A method for separating a gas mixture containing CO2 and at least one component which is nitrogen and / or oxygen and / or argon comprising the steps of: i. the separation of the pressurized gas mixture (GM) during an adsorption (CO2 PSA) and / or membrane permeation (M) step generating a fluid (1) enriched in CO2 and depleted in at least one component compared to the gas mixture and a gas (NW) enriched in at least one component and depleted in CO2 compared to the gas mixture under a pressure greater than 6 bara ii. cooling (RI, R2, R3, R4, R5) of the CO2-enriched fluid producing a cooled CO2-enriched fluid iii. a) a separation of the cooled CO2-enriched fluid from step ii) by partial condensation and / or distillation and / or solidification to produce at least one CO2-rich fluid (9) and at least one CO2-poor fluid (7) comprising a compression step in a compressor (C1, C2, C3, C4, C5, C6, C7) of the CO2-enriched fluid, before or after the cooling of step ii) or of a fluid produced by the low-temperature separation or of a refrigeration cycle and / or the expansion in a turbine (T) of a fluid produced by the low-temperature separation and / or the pressurization in a pump (P) of a liquid produced by the low-temperature separation and / or a regulation step by a pneumatic regulation valve (VI) of a fluid used, to be separated or separated in the low-temperature separation or b) a separation of the cooled CO2-enriched fluid from step ii) by absorption comprising a step of compression in a compressor of the CO2-enriched fluid or of a fluid produced by the absorption separation and a step of separation by absorption of the CO2-enriched fluid by absorption characterized by the use of at least a portion (SGI, SG2, SG3) of the gas enriched in the at least one component as barrier gas of the compressor and / or turbine and / or pump and / or as instrument gas for the pneumatic valve.

2. A method according to claim 1 wherein the at least one CO2-enriched fluid is compressed in the compressor upstream of the low-temperature separation and a compressor barrier system (C1, C2, C3, C4) induces a leak of the barrier gas towards the compressed fluid in the compressor or towards a turbine barrier system (T) induces a leak of the barrier gas towards the expanded fluid in the turbine

3. Method according to one of the preceding claims in which a barrier system of at least one turbine, compressor or pump (T, C5, C6, C7, P) downstream of the separation step a) or b) induces a leak of the compressed gas in the compressor or expanded in the turbine towards the barrier gas.

4. Method according to one of the preceding claims comprising sending the barrier gas and optionally the compressed or expanded gas having leaked towards the barrier gas after passing through at least one rotating machine (C1, C2, C3, C4) upstream of the separation step a) or b).

5. Method according to one of the preceding claims wherein the gas enriched in the at least one component used as barrier and / or instrumentation gas is replaced when it is unavailable by vaporized nitrogen from a liquid nitrogen storage.

6. Method according to one of the preceding claims 1 to 5 wherein the gas enriched in the at least one component used as barrier and / or instrumentation gas is replaced when it is unavailable by vaporized CO2 from a liquid storage or a fluid from the CO2-enriched fluid.

7. Apparatus for separating a gas mixture containing CO2 and at least one component which is nitrogen and / or oxygen and / or argon comprising an adsorption and / or membrane permeation separation unit, means for sending the pressurized gas mixture (GM) into the adsorption (CO2 PSA) and / or membrane permeation (M) unit to be separated, generating a fluid (1) enriched in CO2 and depleted in the at least one component relative to the gas mixture and a gas (NW) enriched in the at least one component and depleted in CO2 relative to the gas mixture under a pressure greater than 6 bara, means (RI, R2, R3, R4, R5)

8. for cooling CO2-enriched fluid producing a cooled CO2-enriched fluid, a separation unit by partial condensation and / or distillation and / or solidification, means for sending cooled CO2-enriched fluid from step ii) by partial condensation and / or distillation and / or solidification to produce at least one CO2-rich fluid (9) and at least one CO2-poor fluid (7), the separation unit comprising a compressor (C1, C2, C3, C4, C5, C6, C7) for compressing CO2-enriched fluid, before or after cooling in the cooling means or a fluid produced by a low-temperature separation or a fluid from a refrigeration cycle and / or comprising a turbine for expanding a fluid produced by the low-temperature separation and / or a pump (P) for pressurizing a liquid produced by the low-temperature separation and / or a pneumatic control valve (VI) for regulating a fluid used,to be separated or separated in the low temperature separation characterized in that it comprises means for sending at least a portion (SGI, SG2, SG3) of the gas enriched in the at least one component to the compressor as compressor barrier gas and / or to the turbine as turbine barrier gas and / or to the pump as pump barrier gas and / or to the pneumatic valve as pneumatic valve instrumentation gas. Apparatus for separating a gas mixture containing CO2 as well as at least one component which is nitrogen and / or oxygen and / or argon comprising an adsorption and / or membrane permeation separation unit, means for sending the pressurized gas mixture (GM) into the adsorption (CO2 PSA) and / or membrane permeation (M) unit to be separated,generating a fluid (1) enriched in CO2 and depleted in at least one component relative to the gas mixture and a gas (NW) enriched in at least one component and depleted in CO2 relative to the gas mixture under a pressure greater than 6 bara, means (RI, R2, R3, R4, R5) for cooling CO2-enriched fluid producing a cooled CO2-enriched fluid, an absorption separation unit, means for sending cooled CO2-enriched fluid to be separated by absorption, the separation unit comprising a compressor for the CO2-enriched fluid or a fluid produced by the absorption separation and an apparatus for absorption separation of the CO2-enriched fluid by absorption characterized in that it comprises, means for sending at least a portion (SGI, SG2, SG3) of the gas enriched in the at least one component to the compressor as compressor barrier gas.

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