A method for capturing CO2 from a mixture containing at least carbon dioxide, at least 1 mole percent oxygen, nitrogen and at least one hydrocarbon

Abstract

The invention relates to a method for capturing CO2 from a mixture (1, 3) containing at least carbon dioxide, at least 1 mol-% or even at least 3 mol-% of oxygen and at least one hydrocarbon, in which method the hydrocarbon is removed from the mixture by catalytic oxidation (CAT) of the oxygen already present in the mixture upstream of the cryogenic separation.

Description

[0001] The present invention relates to a method and apparatus for capturing CO2 from a mixture containing at least carbon dioxide, at least 1 mol% oxygen, nitrogen and at least one hydrocarbon.

[0002] The gas mixture may contain at least carbon dioxide, at least 1 mol% or even less than 3 mol% oxygen, nitrogen, and at least one C2+ or higher carbon dioxide. n H m The hydrocarbon may also contain one of the following compounds: water, argon, at least one nitrogen oxide, at least one sulfur compound, and at least one heavy metal. Preferably, it contains less than 10 mol% or even less than 5 mol% methane.

[0003] Carbon dioxide (CO2) produced by the capture unit can be sequestered in geological structures, such as saline aquifers or depleted gas fields; or used in various possible applications, such as methanol synthesis or the food industry. For the latter application, the specifications regarding the purity of the produced CO2 are more stringent compared to CCS (carbon capture and storage). Furthermore, CO2 capture units used in the food industry are significantly smaller in size due to limited demand. The capture method must be adapted to these specific constraints.

[0004] Existing technology

[0005] Many CO2 capture processes are known to those skilled in the art. Numerous methods exist: capture via chemical or physical absorption, adsorption, or cryogenic separation.

[0006] To achieve the purity of food-grade CO2, a catalytic oxidation (CATOX) stage is typically required to remove trace amounts of hydrocarbons. In this reactor, hydrocarbons react with oxygen (O2) to produce CO2 and water.

[0007] When capturing CO2 from the tail gas of H2 PSA, the mixture contains significant amounts of hydrogen, carbon monoxide, and hydrocarbons (primarily methane). If these molecules are not removed before CATOX, their economic value / total calorific value will be lost in CATOX. Therefore, it is preferable to extract these molecules before CATOX. In this case, the existing technology involves installing such a catalytic reactor downstream of the capture process. Figure 1 Therefore, a second dryer must be installed (to remove the water produced by the reaction) and a second separation must be performed (to remove excess O2).

[0008] Food-grade CO2 can be produced from nearly pure CO2 via a liquefaction unit. CATOX is then used only to remove trace amounts of hydrocarbons. In this case, CATOX is installed upstream of the dryer and the cryogenic separation of impurities lighter than CO2. Figure 2This allows for the installation of only a single dryer, and the separation of O2 and CO2 only once.

[0009] The problem solved by this invention

[0010] Food-grade CO2 can also be produced from flue gas. However, these flue gases contain compounds not found in existing CO2 sources. The flue gas may contain nitrogen oxides (NOx), sulfur-based impurities, or heavy metals. It is still usable. Figure 1 However, this invention offers a more competitive configuration.

[0011] Some CATOX catalysts (containing palladium) are poisoned by the presence of sulfur compounds. Two options are considered: select a sulfur-resistant catalyst or remove the sulfur compounds before CATOX.

[0012] Catalysts resistant to sulfur compounds can be more expensive and typically require higher temperatures to achieve the same performance qualities. These resistant catalysts allow for the use of... Figure 2 The existing technological solutions; however, their performance degradation does not make this configuration competitive.

[0013] Activated carbon is a good adsorbent for sulfur-based impurities; however, other impurities present in flue gas, such as NOx or heavy hydrocarbons, will also be adsorbed onto it. Therefore, most impurities must be removed before adsorption and separation with activated carbon to avoid rapid saturation. Washing with liquid CO2 is effective in preventing molecules with lower volatility than CO2 (such as NO2 or heavy hydrocarbons).

[0014] This invention provides a novel approach in which a catalytic oxidation reactor is integrated within a CO2 capture unit. Impurities incompatible with CATOX are removed before the reactor.

[0015] This approach enables the production of food-grade CO2 with a limited number of equipment projects, thus reducing the capital cost of CO2 capture units.

[0016] According to one aspect of the invention, a method is provided for capturing CO2 from a mixture containing at least carbon dioxide, at least one component with lower volatility than CO2, at least 1 mol% or even at least 3 mol% oxygen, nitrogen, and at least one C2 or higher component. n H m The method comprises the following stages: hydrocarbons, and may also contain one of the following compounds: water, argon, at least one nitrogen oxide, at least one sulfur compound, and at least one heavy metal. i) Compress the mixture. ii) Dry the compressed mixture, iii) Cool the compressed and dried mixture in a heat exchanger. iv) Purify the compressed and dried mixture to produce a fluid enriched relative to the mixture with at least one component with lower volatility than CO2, and a fluid depleted relative to the mixture with at least one component with lower volatility than CO2 and enriched with at least one component with higher volatility than CO2. v) Heating the fluid depleted of at least one component with a volatility lower than CO2 in a heat exchanger. vi) Catalytically oxidizing the fluid depleted of at least one component with a volatility lower than CO2 at a temperature of less than or equal to 520°C to produce a C2-depleted fluid containing water derived from oxidation. n H m Hydrocarbon fluids, vii) Drying the fluid that has depleted at least one hydrocarbon, and viii) The dried fluid from stage vii) is cooled in a heat exchanger and separated by partial condensation and / or by distillation and / or by desublimation to obtain a liquid enriched with CO2 relative to the mixture and a gas depleted with CO2 relative to the mixture.

[0017] Other optional themes according to the invention: Phase iv) consists of a washing phase using liquid CO2 at temperatures below -50°C. • Stage iv) Produces a fluid that is depleted of at least one component with lower volatility than CO2 relative to the mixture and enriched with oxygen. If the mixture to be treated contains at least one sulfur compound, an adsorption separation stage is added between stage iv) and catalytic oxidation. If the mixture to be treated contains mercury, a second adsorption separation stage is added between stage iv) and catalytic oxidation. The CO2-enriched liquid contains less than 50 ppmv, preferably less than 10 ppmv, of total hydrocarbons as methane equivalent and less than 20 ppmv, preferably less than 5 ppmv, of total hydrocarbons other than methane as methane equivalent.

[0018] According to the methane equivalence principle, a molecule containing two carbon atoms is counted as two methane equivalents, a molecule containing three carbon atoms is counted as three methane equivalents, and so on.

[0019] • The dried fluid in stage vii) contains oxygen, and the separation in stage viii) includes at least one partial condensation stage and optionally a distillation stage, wherein the dried fluid cooled in a heat exchanger is partially condensed in the heat exchanger and separated in a phase separator into an oxygen-rich and CO2-depleted gas and an oxygen-depleted and CO2-depleted liquid, the oxygen-depleted liquid being separated or constituting a CO2-rich product by being fed to the top of a distillation column. The oxygen-enriched gas is heated in a heat exchanger and downstream of the exchanger, residual oxygen is removed by permeation separation to form a recirculated gas containing CO2, which is mixed with the mixture in either stage i) or ii). • No oxygen flow was added upstream of the catalytic oxidation process to the fluid that was depleted of at least one component with a volatility lower than CO2. The mixture contains less than 10 mol% or even less than 5 mol% methane.

[0020] According to another aspect of the invention, an apparatus is provided for capturing CO2 from a mixture containing at least carbon dioxide, at least one component with lower volatility than CO2, at least 1 mol% or even at least 3 mol% oxygen, nitrogen, and at least one C2 component. n H m The apparatus comprises a hydrocarbon, and may also contain one of the following compounds: water, argon, at least one nitrogen oxide, at least one sulfur compound, and at least one heavy metal. The apparatus includes a compressor for compressing the mixture; a first dryer for drying the compressed mixture; a heat exchanger for cooling the compressed and dried mixture; means for purifying the compressed and dried mixture cooled in the heat exchanger to produce a fluid enriched with at least one component with a volatility lower than CO2 relative to the mixture and a fluid depleted with at least one component with a volatility lower than CO2 relative to the mixture and enriched with at least one component with a volatility higher than CO2; a conduit connected to the means for purifying the mixture and connected to the heat exchanger to feed the fluid depleted with at least one component with a volatility lower than CO2 into the heat exchanger for heating; a catalytic oxidation unit capable of operating at a temperature less than or equal to 520°C; means for feeding the fluid depleted with at least one component with a volatility lower than CO2, heated in the heat exchanger, to the catalytic oxidation unit; a second dryer; and means for drying the fluid from the oxidation unit depleted with at least one component with a volatility greater than or equal to C2. n H mThe system includes a conduit for feeding an aqueous fluid containing hydrocarbons to a second dryer to produce a dry fluid depleted of at least one hydrocarbon; a conduit for feeding the dry fluid depleted of at least one hydrocarbon to the heat exchanger; a device for separation by partial condensation and / or by distillation and / or by desublimation; a conduit for feeding the dry fluid depleted of at least one hydrocarbon, cooled in the heat exchanger, to the separation device; a conduit for discharging a liquid enriched with CO2 relative to the mixture from the separation device; and a conduit for discharging a gas depleted with CO2 relative to the mixture from the separation device. Invention Details

[0022] The invention will now be described in more detail with reference to the accompanying drawings, in which: [ Figure 1 [This represents another method that is not part of the present invention.]

[0023] [ Figure 2 [] represents the method according to the present invention.

[0024] [ Figure 1 This represents a method in which gas 1 is compressed in a compressor having four stages C1, C2, C3, C4, followed by coolers R1, R2, R3, R4 after each stage. Gas 1 contains at least carbon dioxide, at least one component less volatile than CO2 (e.g., NO2), at least 1 mol% or even at least 3 mol% oxygen, nitrogen, and at least one C2 or higher C4 component. n H m A mixture of hydrocarbons, which may also contain one of the following compounds: water, argon, at least one nitrogen oxide, at least one sulfur compound, and at least one heavy metal. Cooling produces condensates W1, W2, W3, and W4, which are collected to form stream W. The compressed mixture is dried by temperature-switching adsorption in adsorption unit TSA1. The dried mixture is cooled in heat exchanger E1 and exits the exchanger at an intermediate temperature for separation in scrubbing tower K1, which is top-fed liquid CO2 33. This tower produces a liquid 5 enriched with the at least one component with lower volatility than CO2 relative to mixture 1, and a gas 3 depleted with the at least one component with lower volatility than CO2 relative to the mixture and enriched with at least one component with higher volatility than CO2, particularly oxygen. Liquid 5 is vaporized by heater H1 and mixed with gas 1.

[0025] Gas 3 is cooled to the cold end in heat exchanger E1, where it partially condenses. This two-phase flow is then sent to phase separator S1 to produce gas 7 and liquid 9. Gas 7 is heated in heat exchanger E1 and separated by permeation M to form CO2-enriched permeate gas 11 (which is recycled to gas 1 upstream of C1) and permeate residue 13 (which is waste gas).

[0026] Liquid 9 is expanded and fed to the top of tower K2. Tower K2 produces gas 15 enriched with at least one component more volatile than CO2 at the top and liquid 17 depleted of the at least one component more volatile than CO2 at the bottom. Gas 15 is heated in heat exchanger E1 and fed between cooler R3 and compressor C4. Liquid 17 is vaporized and heated in heat exchanger E1, and the resulting gas is mixed with gaseous oxygen 19. The resulting gas 21 is heated in heat exchanger E2, heated by heater H2, and fed to catalytic oxidation unit CAT, where at least one component with a C content greater than or equal to C2 is produced. n H m Hydrocarbons react with oxygen to form water. Gas 23 exits the oxidation unit CAT and is cooled in exchanger E2, followed by cooling in cooler R5. The cooled gas 23 is dried in the second temperature-switching adsorption unit TSA2 to produce dry gas 24, which is cooled in heat exchanger E2. Gas 24 is expanded to form a liquid at the top of column K3. A CO2-rich product 27 is produced at the bottom of column K3, a portion 29 of which constitutes the product. Another portion 31 is vaporized in the heat exchanger and sent to the bottom of column K3 as reboiler gas. Another portion 33 is the washing liquid from column C1.

[0027] Unit TSA1 produces condensate W6. Unit TSA2 produces humid gas W5.

[0028] Figure 2 and Figure 1 The difference is that tower K2, which reduces the content of at least one component with higher volatility than CO2, no longer exists, and no oxygen flow is added upstream of the catalytic oxidation, as the oxygen present in gas 1 is sufficient to supply the catalytic oxidation.

[0029] The dried mixture is cooled in heat exchanger E1 and exits the exchanger at an intermediate temperature for separation in scrubbing tower K1, which is topped with liquid CO2 33. This tower produces a liquid 5 enriched relative to mixture 1 with at least one component less volatile than CO2, and a gas 3 depleted relative to the mixture with at least one component less volatile than CO2 and enriched with at least one component more volatile than CO2, particularly oxygen. Liquid 5 is vaporized by heater H1 and mixed with gas 1.

[0030] If the mixtures 1 and 3 to be treated contain sulfur compounds, an adsorption separation stage is added between CO2 washing and catalytic oxidation of CAT in K1.

[0031] If the mixtures 1 and 3 to be treated contain mercury, an adsorption separation stage is added between CO2 washing and catalytic oxidation of CAT in K1.

[0032] Gas 3 is heated in heat exchangers E1 and E2 and then further heated by heater H2. The heated gas 3 is then sent to the catalytic oxidation unit CAT, where at least one C2 is present. n H m Hydrocarbons react with oxygen to form water. Gas 4 exits the oxidation unit CAT and is cooled in exchanger E2, then in cooler R5. The cooled gas 4 is dried in the second temperature-switching adsorption unit TSA2 to produce dry gas 24, which is cooled in heat exchanger E2 and partially condensed therein. The two-phase flow is separated in phase separator S1. Gas 9 from separator S1 is expanded to form a liquid at the top of column K3. A CO2-rich product 27 is produced at the bottom of column K3 and sent to a pump to form a pressurized liquid, a portion of which 29 constitutes the product. Another portion 31 is vaporized in the heat exchanger and sent to the bottom of column K3 as a reboiler gas. Another portion 33 is the washing liquid from column C1.

[0033] Tower K3 may not exist. Partial condensation may include at least two partial condensation stages. Separation may include a desublimation stage.

[0034] Gas 25 from tower K3 is heated in heat exchanger E1, still containing oxygen, and separated by permeate M to form CO2-enriched and oxygen-depleted permeate 8, which is sent upstream of compressor C1 to mix with gas 1. Gas 10, depleted of CO2 and enriched with oxygen, serves as exhaust gas.

[0035] Unit TSA1 produces condensate W6. Unit TSA2 produces humid gas W5.

Claims

1. A method for capturing CO2 from a mixture, said mixture containing at least carbon dioxide, at least one component with lower volatility than CO2, at least 1 mol% or even at least 3 mol% oxygen, nitrogen, and at least one C2 or higher component. n H m The method comprises the following stages: hydrocarbons, and may also contain one of the following compounds: water, argon, at least one nitrogen oxide, at least one sulfur compound, and at least one heavy metal. i) Compress (C1, C2, C3, C4) the mixture (1), ii) Drying (TSA1) the compressed mixture, iii) Cool the compressed and dried mixture in a heat exchanger (E1), iv) Purify (K1) the compressed and dried mixture to produce a fluid enriched relative to the mixture with at least one component with lower volatility than CO2 and a fluid depleted relative to the mixture with at least one component with lower volatility than CO2 and enriched with at least one component with higher volatility than CO2 (3). v) Heating the fluid depleted of at least one component with a volatility lower than CO2 in a heat exchanger. vi) Catalytic oxidation (CAT) of a fluid depleted of at least one component with volatility lower than CO2 at a temperature less than or equal to 520°C to produce a C2-depleted fluid containing water derived from the oxidation of the fluid. n H m Hydrocarbon fluid (4). vii) Drying (TSA2) the fluid depleted of the at least one hydrocarbon, and viii) The dried fluid from stage vii) is cooled in a heat exchanger and separated by partial condensation and / or by distillation and / or by desublimation (S1, K3) to obtain a liquid (9, 27, 29, 31) enriched with CO2 relative to the mixture and a gas (7, 25) depleted with CO2 relative to the mixture.

2. The method according to the preceding claim, wherein stage iv) consists of a stage of washing with liquid CO2 (33) at a temperature below -50°C.

3. The method according to claim 1 or 2, wherein if the mixture to be treated contains at least one sulfur compound, an adsorption separation stage is added between stage iv) and catalytic oxidation (CAT).

4. The method according to any one of the preceding claims, wherein if the mixture to be treated contains mercury, a second adsorption separation stage is added between stage iv) and catalytic oxidation (CAT).

5. The method according to any one of the preceding claims, wherein the CO2-enriched liquid (27, 29, 31) contains less than 50 ppmv, preferably less than 10 ppmv, of total hydrocarbons as methane equivalent and less than 20 ppmv, preferably less than 5 ppmv, of total hydrocarbons other than methane as methane equivalent.

6. The method according to any one of the preceding claims, wherein the fluid (4) dried in stage vii) contains oxygen, and the separation (S1, K3) in stage viii) includes at least one partial condensation stage and optionally a distillation stage, wherein the dried fluid cooled in a heat exchanger (E1) is partially condensed in the heat exchanger and separated in a phase separator into an oxygen-rich and CO2-depleted gas (7) and an oxygen-depleted and CO2-depleted liquid (9), the oxygen-depleted liquid being separated or constituting a CO2-rich product by being fed to the top of a distillation column (K3).

7. The method according to claim 6, wherein the oxygen-enriched gas (7) is heated in a heat exchanger (E1) and downstream of the exchanger is permeation separation (M) to remove residual oxygen to form a recirculated gas (8) containing CO2, which is mixed with the mixture in either stage i) or ii).

8. The method according to any one of the preceding claims, wherein no oxygen flow is added upstream of the catalytic oxidation (CAT) to the fluid (3) that depletes the at least one component with a volatility lower than CO2.

9. The method according to any one of the preceding claims, wherein the mixture contains less than 10 mol% or even less than 5 mol% methane.

10. An apparatus for capturing CO2 from a mixture (1), said mixture (1) containing at least carbon dioxide, at least one component with lower volatility than CO2, at least 1 mol% or even at least 3 mol% oxygen, nitrogen, and at least one C2 or greater. n H m The mixture contains hydrocarbons and may also contain one of the following compounds: water, argon, at least one nitrogen oxide, at least one sulfur compound, and at least one heavy metal. The apparatus includes a compressor (C1, C2, C3, C4) for compressing the mixture, a first dryer (TSA1) for drying the compressed mixture, a heat exchanger (E1) for cooling the compressed and dried mixture, and a fluid for purifying the compressed and dried mixture cooled in the heat exchanger to produce a fluid enriched with the at least one component with lower volatility than CO2 relative to the mixture and a fluid depleted with the at least one component with lower volatility than CO2 relative to the mixture. The apparatus (K1) enriches a fluid (3) containing at least one component with a volatility higher than CO2; a device (K1) connected to a device for purifying the mixture and a pipe connected to the heat exchanger to feed the fluid (3) depleted of the at least one component with a volatility lower than CO2 into the heat exchanger for heating; a catalytic oxidation (CAT) unit capable of operating at a temperature less than or equal to 520°C; a device for feeding the fluid (3) depleted of the component with a volatility lower than CO2 heated in the heat exchanger to the catalytic oxidation unit; a second dryer (TSA2); and a device for drying the fluid (3) from the oxidation unit depleted of the at least one component with a volatility greater than or equal to C2. n H m A conduit for feeding an aqueous fluid containing hydrocarbons to a second dryer to produce a dry fluid depleted of at least one hydrocarbon; a conduit for feeding the dry fluid depleted of at least one hydrocarbon to the heat exchanger; a device (S1, K3) for separation by partial condensation and / or by distillation and / or by desublimation; a conduit for feeding the dry fluid depleted of at least one hydrocarbon, cooled in the heat exchanger, to the separation device; a conduit (9, 27, 29, 31) for discharging a liquid enriched with CO2 relative to the mixture from the separation device; and a conduit (7, 25) for discharging a gas depleted with CO2 relative to the mixture from the separation device.

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