Method for enhanced carbon capture in electrolysis processes - Patents.com

Abstract

A method for scrubbing a gas containing carbon dioxide to deplete carbon dioxide (CO2) from the gas, the method comprising scrubbing the gas in a scrubber (210) with a first alkaline aqueous scrubbing solution to remove the carbon dioxide (CO2) from the gas by converting it into bicarbonate (HCO3 - ) and / or as carbonate (CO3 2- ) in the first alkaline aqueous wash, resulting in bicarbonate (HCO3 - ) and / or carbonate (CO3 2- The method includes the steps of: providing a first used aqueous cleaning solution containing hydrogen carbonate (HCO3), supplying the first used aqueous cleaning solution to an electrolysis cell (310) having an anode chamber (313) and a cathode chamber (312), regenerating the first used aqueous cleaning solution in the electrolysis cell (310) by electrolysis, and extracting hydrogen carbonate (HCO3) from the first used aqueous cleaning solution in the anode chamber (313). - ) and carbonate (CO3 2- ), wherein the regeneration further comprises generating gaseous hydrogen in the cathode chamber (312) and a gaseous mixture of oxygen and carbon dioxide (CO2) in the anode chamber (313) by electrolysis, withdrawing the regenerated alkaline aqueous cleaning solution from the cathode chamber (312) and recycling it to the scrubber (210), wherein the carbon dioxide (CO2) and / or oxygen (O2) withdrawn from the anode chamber (313) is compressed in a compression unit (330) to a liquid and compressing the liquid carbon dioxide from the gaseous oxygen into carbon dioxide and compressed oxygen (O2), the method further comprising separating the liquid carbon dioxide from the gaseous oxygen in a gas separator (340) into a first stream (S1) comprising carbon dioxide and a second stream (S2) comprising oxygen containing less than 30% carbon dioxide, wherein the second stream (S2) is introduced into at least a portion of the first used aqueous cleaning solution before feeding the first used aqueous cleaning solution to the anode compartment of an electrolysis cell (310).

Description

[Technical field]

[0001] The present invention relates to a method for increasing the uptake of carbon dioxide (CO2) in an electrolytic regeneration process of spent cleaning solution from a scrubbing process in which CO2 is depleted from a gas such as a flue gas or exhaust gas, and further relates to a system for such increased uptake of CO2 from the spent cleaning solution in the regeneration process. [Background technology]

[0002] Carbon dioxide (CO2) is a gas that, when emitted into the atmosphere, has a negative impact on the climate, as it contributes to the greenhouse effect and the rise in global temperature. Carbon dioxide is produced, for example, as a by-product when fossil fuels, such as coal, gasoline or diesel fuel, are burned. Coal- and gas-fired power plants are responsible for a large share of CO2 emissions. Reducing carbon dioxide emissions is a goal for many sectors.

[0003] The exhaust gases resulting from combustion and containing CO2 are typically referred to as flue gases or exhaust gases. Depleting such exhaust gases of CO2 by lowering the CO2 content in the exhaust gases can be done by so-called gas scrubbing, i.e. removing the CO2 from the gas stream by absorbing / dissolving it in a liquid. The main application of CO2 scrubbing is the removal of CO2 from the exhaust (i.e. flue gas) of coal-fired and gas-fired power plants downstream of the power plant before the gas is released into the atmosphere. By using such processes it is possible to significantly lower the CO2 emissions associated with coal-fired power generation. In the chemical industry, CO2 scrubbing is used, for example, to separate CO2 from natural gas for use in the beverage or fertilizer sector.

[0004] Through DAC (Direct Air Capture), carbon dioxide is collected from ambient air, i.e. the air is purified from carbon dioxide, which can be compressed for further downstream use or storage, e.g. underground storage.

[0005] In a CO2 scrubbing system, a scrubbing solution captures carbon dioxide from the flue gas at low temperatures in an absorber.

[0006] US11219860 discloses such a process for carbon capture, in which the spent cleaning solution is regenerated in an electrolytic process. The regeneration process produces a regenerated alkaline aqueous cleaning solution from the cathode chamber, which recirculates the regenerated alkaline aqueous cleaning solution to the scrubber, and produces a stream of a gaseous mixture of carbon dioxide and oxygen from the anode chamber. The gaseous mixture from the anode chamber can be compressed and cooled to pure liquid carbon dioxide that can be used for downstream applications, and a portion of the CO2 is released to the surrounding environment as an off-gas that also typically contains a large proportion of oxygen.

[0007] There is an urgent need for improved scrubbing systems that increase the efficiency of overall carbon capture. Summary of the Invention

[0008] It is with respect to these considerations and others that the embodiments described in this disclosure have been made.

[0009] It is an object of the present disclosure to provide an improved method and system for increasing carbon dioxide (CO2) uptake in an electrolytic regeneration process.

[0010] The invention is defined by the accompanying independent claims. Embodiments are set out in the accompanying dependent claims and the following description.

[0011] According to a first aspect, there is provided a method for scrubbing a gas containing carbon dioxide to deplete carbon dioxide (CO2) from the gas, the method comprising scrubbing the gas in a scrubber with a first alkaline aqueous scrubbing liquid to remove the carbon dioxide from the gas by depleting it with hydrogen carbonate (HCO3 - ) and / or as carbonate (CO3 2-) in the first alkaline aqueous wash, resulting in bicarbonate (HCO3 - ) and / or carbonate (CO3 2- The method includes the steps of: providing a first used aqueous cleaning solution containing hydrogen carbonate (HCO3), supplying the first used aqueous cleaning solution to an electrolysis cell (310) having an anode chamber (313) and a cathode chamber (312), regenerating the first used aqueous cleaning solution in the electrolysis cell (310) by electrolysis, and extracting hydrogen carbonate (HCO3) from the first used aqueous cleaning solution in the anode chamber (313). - ) and carbonate (CO3 2- ), wherein the regeneration further comprises generating gaseous hydrogen in the cathode chamber (312) and a gaseous mixture of oxygen and carbon dioxide (CO2) in the anode chamber (313) by electrolysis; withdrawing the regenerated alkaline aqueous cleaning solution from the cathode chamber and recycling it to the scrubber; wherein the carbon dioxide (CO2) and / or oxygen (O2) withdrawn from the anode chamber is compressed in a compression unit into liquid carbon dioxide and compressed oxygen (O2); the method further comprises separating the liquid carbon dioxide from the gaseous oxygen in a gas separator into a first stream comprising carbon dioxide and a second stream comprising oxygen containing less than 30% carbon dioxide, wherein the second stream is introduced into at least a portion of the first spent aqueous cleaning solution before supplying the first spent aqueous cleaning solution to the anode chamber of the electrolysis cell.

[0012] Typically, the second stream contains about 20% carbon dioxide and about 80% oxygen.

[0013] The spent wash solution from the first wash stage is fed to an electrolytic cell to be regenerated.

[0014] In electrolysis, water is converted at the anode into oxygen and hydronium ions (HO + ) while water is converted to hydrogen and hydroxide ions (OH -) in the anode chamber from the first spent aqueous cleaning solution by increasing the pH of the first spent aqueous cleaning solution in the cathode chamber and decreasing the pH to shift the equilibrium towards carbonic acid, which in turn shifts towards carbon dioxide. - ) and carbonate (CO3 2- ). The regeneration further comprises generating gaseous hydrogen in the cathode chamber and a gaseous mixture of oxygen and carbon dioxide in the anode chamber by electrolysis. A description of the chemical reactions and operation of the process is further described in the detailed description herein below.

[0015] The method further comprises withdrawing the regenerated alkaline aqueous cleaning solution from the cathode chamber and recycling it to the scrubber.

[0016] Additionally, regeneration, as already explained, also generates carbon dioxide and hydrogen, which can be used downstream for the synthesis of organic compounds such as methanol, thus adding further value to the process. This process is ideal for processes such as downstream Power-to-X processes and thus the need to increase the overall carbon capture of the cleaning process.

[0017] Gaseous hydrogen is withdrawn from the cathode chamber and a gaseous mixture of oxygen and carbon dioxide is withdrawn from the anode chamber.

[0018] Extracting hydrogen, oxygen and carbon dioxide from the regenerative process is advantageous because the hydrogen and oxygen can be used to generate electricity to partially operate the process, for example by means of a fuel cell. Furthermore, the hydrogen and carbon dioxide (CO2) can be used for the synthesis of organic compounds, for example methanol, thereby compensating for the operating costs of the process.

[0019] The gaseous mixture of oxygen and carbon dioxide may be compressed in a first compression unit to provide separation of liquid carbon dioxide (CO2) from gaseous (O2) in a separation unit.

[0020] The method therefore comprises separating this gaseous mixture of oxygen and carbon dioxide into a carbon dioxide-rich and oxygen-depleted first stream and an oxygen-rich second stream having a carbon dioxide content in the range of 5-25%, a second gas stream or "off-gas", where both streams are compressed and cooled.

[0021] According to this method, this second stream, or off-gas, which is compressed and cooled, is mixed with the spent aqueous wash liquid prior to introduction into the electrolytic cell.

[0022] The carbon capture reaction in the scrubbing step is carried out automatically, therefore operation of the scrubber is an automatic process and requires no power other than that required to circulate the liquid.

[0023] The regeneration process, which takes place in the cathode and anode compartments of the electrolysis cell, is an electrochemical reaction, which essentially requires electrical power. This electrochemical process regenerates the solvent and produces hydrogen at the cathode and a mixture of carbon dioxide (CO2) and oxygen at the anode. According to the above-mentioned method, during regeneration, the pH of the cleaning solution increases. Carbon dioxide is dissolved and the equilibrium is shifted to bicarbonate (HCO3 - ) and carbonate (CO3 2- ), the first aqueous cleaning solution needs to be alkaline, i.e., have a pH greater than 7, e.g., a pH of 8 or greater. According to the method of the present invention, by introducing CO2 from the off-gas into the first used aqueous cleaning solution, the pH of the cleaning solution will be optimized, and thus the energy used in the electrolysis cell can be optimized. Thus, the introduction of additional CO2 into the used cleaning solution reduces the potential carbonate (CO3 2- ) to (HCO3 - ), making the entire cleaning process more efficient as CO2 that would otherwise be lost to the ambient air in the "off-gas" is reintroduced into the system.

[0024] The actual electricity consumption will depend on the technical implementation of the process. Overall, the process requires a large amount of electrical energy, not heat. This is positive, since the regenerative electrification of the carbon capture process is highly desirable. Furthermore, part of the energy can be recovered as heat for district heating.

[0025] This will reduce the amount of CO2 in the "off-gas" and introduce a higher carbon load into the first spent aqueous cleaning solution prior to or at the same time as the first spent aqueous cleaning solution is introduced into the electrolytic cell system. The second gas stream or "off-gas" is pressurized and cooled, which will improve CO2 uptake in the first spent aqueous cleaning solution. The introduction of the "off-gas" into the first spent aqueous cleaning solution will be in a vessel suitable for pressurization, e.g., the first spent aqueous solution will be pressurized and cooled by the introduction of the off-gas.

[0026] The gas to be depleted of carbon dioxide can be any one of flue gas, exhaust gas, or ambient air.

[0027] The pH of the first spent aqueous liquid may be in the range of 8 to 11 prior to the introduction of a second stream of gas, said introduction increasing the carbon loading of said spent aqueous liquid by 2 to 10%, or 3 to 7%, or 4 to 6%.

[0028] By increasing the carbon loading in the spent aqueous liquor by at least 2%, most preferably about 5%, i.e. 5.5%, the amount of carbon in the gaseous mixture withdrawn from the electrolytic cell is increased, which in turn reduces the energy required to compress the gas. In a further aspect, the increased carbon loading of the system also results in a reduction in the amount of scrubbing liquor required in the scrubbing system, which results in a reduction in the size required for the scrubber. By increasing this loading by about 5%, less scrubbing liquor is required and a 10-20% savings in scrubber sizing can be achieved. It has been shown that significant energy and cost savings can be achieved by using less scrubbing liquor.

[0029] The first spent aqueous washing solution may be separated into at least two streams after exiting the scrubber, where the second stream of compressed gas comprising oxygen containing less than 30% carbon dioxide is introduced into at least one of the first spent aqueous washing solution streams, and at least another of the first spent aqueous washing solution streams is fed directly to an electrolysis cell.

[0030] According to a second aspect, there is provided a system for scrubbing a gas, such as a flue gas or exhaust gas, containing carbon dioxide, to deplete carbon dioxide from the flue gas, the system comprising: - ) and / or as carbonate (CO3 2-) comprising a scrubber apparatus for scrubbing gas with an alkaline aqueous scrubbing liquid for dissolving in the alkaline aqueous scrubbing liquid, and a regeneration apparatus for regenerating the spent aqueous scrubbing liquid by electrolysis, wherein the scrubber apparatus comprises a scrubber having an inlet for the gas to be scrubbed and an outlet for carbon dioxide depleted gas, the scrubber further comprising an inlet for receiving the alkaline aqueous scrubbing liquid and an outlet for withdrawing the spent aqueous scrubbing liquid, the regeneration apparatus comprising an electrolysis cell comprising an anode chamber and a cathode chamber, the anode chamber having an anode inlet for receiving the spent aqueous scrubbing liquid and an anode outlet for withdrawing oxygen and carbon dioxide, the cathode chamber having an anode inlet for receiving the regenerated aqueous scrubbing liquid and an anode outlet for withdrawing oxygen and carbon dioxide, the cathode chamber having an anode inlet for receiving the regenerated aqueous scrubbing liquid and an anode outlet for withdrawing oxygen and carbon dioxide, the cathode chamber having an anode inlet for receiving the regenerated aqueous scrubbing liquid and an anode outlet for withdrawing oxygen and carbon dioxide, the cathode chamber having an anode inlet for receiving the regenerated aqueous scrubbing liquid and an anode outlet for withdrawing oxygen and carbon dioxide, the cathode chamber having an anode inlet for receiving the regenerated aqueous scrubbing liquid and an anode outlet for withdrawing oxygen and carbon dioxide, the anode chamber having an anode outlet ... the outlet for the spent aqueous cleaning liquid of the scrubber is in flow communication with the inlet for the spent aqueous cleaning liquid of the anode chamber and the outlet for the regenerated aqueous cleaning liquid of the cathode chamber is in flow communication with the inlet for the alkaline aqueous cleaning liquid of the scrubber, the regenerator further comprising a first compressor unit for compressing the oxygen and carbon dioxide withdrawn from the anode chamber, the regenerator further comprising a gas separator for separating the oxygen and carbon dioxide withdrawn from the anode chamber into a first stream which is a liquefied carbon dioxide stream and a second stream comprising compressed gaseous oxygen containing less than 30% carbon dioxide, wherein the gas separator is in flow connection with at least a portion of the spent aqueous cleaning liquid.

[0031] According to a second aspect, the system may further comprise a mixing zone for introducing the compressed second stream into the spent aqueous cleaning solution prior to or simultaneously with feeding the spent aqueous cleaning solution to the electrolytic cell.

[0032] Alternatively, the system may further comprise a second compressor unit for further compressing at least a portion of the second stream of gaseous oxygen containing less than 30% carbon dioxide.

[0033] The mixing zone may comprise a vessel adapted to be pressurized and disposed between the outlet for the spent aqueous cleaning liquid of the scrubber and the inlet for the spent aqueous cleaning liquid of the anode chamber, wherein the vessel is in flow communication with the gas separator for separating oxygen and carbon dioxide and / or with the second compressor unit, as well as with the scrubber outlet and the anode inlet.

[0034] According to the system of the second aspect, a mixing zone may be disposed at the anode inlet, wherein the gas separator for separating oxygen and carbon dioxide and / or the second compressor unit are further in flow communication with the anode inlet.

[0035] According to a third aspect, bicarbonate (HCO3) is used in electrolysis to provide an alkaline aqueous cleaning solution. - ) and / or carbonate (CO3 2- There is provided a regeneration apparatus for regenerating a spent aqueous cleaning solution comprising: a first aqueous cleaning solution and a second aqueous cleaning solution comprising hydrogen; a second aqueous cleaning solution and a third aqueous cleaning solution; a second aqueous cleaning solution and a fourth aqueous cleaning solution; a second aqueous cleaning solution and a fourth aqueous cleaning solution; a second aqueous cleaning solution and a fourth aqueous cleaning solution; a second aqueous cleaning solution and a fourth aqueous cleaning solution; a second aqueous cleaning solution and a fourth aqueous cleaning solution; a second aqueous cleaning solution and a fourth aqueous cleaning solution;

[0036] This means that the second stream of cooled and compressed off-gas is in flow connection with the first spent aqueous wash liquid.

[0037] The regenerator may further comprise a mixing zone for introducing the compressed second stream into the spent aqueous wash solution prior to or simultaneously with feeding the spent aqueous wash solution to the electrolytic cell.

[0038] The regenerator may further comprise a second compressor unit for further compressing the second stream comprising gaseous oxygen containing less than 30% carbon dioxide.

[0039] The mixing zone may comprise a vessel adapted to be pressurized and disposed between an outlet for the spent aqueous cleaning liquid of the scrubber and an inlet for the spent aqueous cleaning liquid of the anode chamber, said vessel being in flow communication with said gas separator for separating oxygen and carbon dioxide and / or with said second compressor unit, as well as with said scrubber outlet and said anode inlet.

[0040] The mixing zone may be disposed at the inlet of the anode chamber, the gas separator for separating oxygen and carbon dioxide, and / or the second compressor unit being further in flow communication with the anode inlet.

[0041] The higher partial pressure of CO2 in the gas and the lower temperature of the liquid will improve the uptake of CO2 into the liquid, and the first spent aqueous wash liquid will absorb CO2 from the "off-gas" and at the same time be pressurized before being introduced into the electrolyser.

[0042] The introduction of additional carbon dioxide into the first spent cleaning solution, i.e., increased carbon loading, increases the potential carbonate CO 2- HCO3 - , thus lowering the pH value of the first used cleaning solution before it enters the electrolysis cell. The lowered pH will increase the efficiency of the electrolysis cell unit for CO2 release, making the overall carbon capture more efficient.

[0043] Another advantage is that when the first flushing liquid enters the electrolysis cell unit, the first flushing liquid will have an increased pressure, which will result in the electrolysis cell being operated at a higher pressure, which will improve the energy efficiency of the electrolyzer system; in turn, the increased or higher pressure will also result in reduced energy consumption for CO2 / O2 separation of the gaseous mixture withdrawn from the anode chamber as well as for H2 pressurization of the gas withdrawn from the cathode chamber, since the starting pressure for the operation of these units will be higher than ambient pressure.

[0044] According to a second aspect, in a corresponding manner, there is provided a system for scrubbing a gas, such as a flue gas or exhaust gas, that contains carbon dioxide, for depleting the carbon dioxide from the flue gas.

[0045] Typically, a first gas separator is disposed downstream of the second compressor unit to provide a first stream of liquid carbon dioxide and a second stream comprising gaseous oxygen containing less than 30% carbon dioxide, or preferably less than 25% carbon dioxide, or "off-gas", i.e., second gas stream. Preferably, the carbon dioxide content in the second stream or gas is in the range of 5-25%.

[0046] The regenerator may further comprise a second compressor unit 395 for compressing and cooling the second gas stream.

[0047] The regenerator includes a mixing zone in which the second stream or off-gas is mixed with the first spent aqueous wash liquid.

[0048] The mixing zone may be a vessel or tank adapted for pressurization into which the first spent aqueous liquid is introduced and mixed with the second stream of cooled and compressed (pressurized) off-gas. The vessel is thus in flow communication with both the outlet for the spent aqueous cleaning liquid of the scrubber and the inlet for the spent aqueous cleaning liquid of the anode chamber, as well as with the second compression unit.

[0049] Alternatively, the mixing zone is located at the inlet of the anode chamber, meaning that there can be a combined inlet for the second gas and the spent aqueous liquid, so that mixing occurs in a zone close to the inlet, or the spent aqueous liquid and the second stream of gas are fed separately to the anode chamber, so that mixing occurs within the anode chamber.

[0050] Although the present invention has been described above with reference to specific embodiments, it is not intended that the present invention be limited to the specific form set forth herein. Rather, the present invention is limited only by the appended claims, and other embodiments than the specific embodiments described above are equally possible within the scope of these appended claims.

[0051] In the claims, the term "comprises / comprising" does not exclude the presence of other elements or steps. Additionally, although individual features may be included in different claims, these features may in some cases be advantageously combined, and the inclusion in different claims does not imply that a combination of these features is not feasible and / or advantageous.

[0052] In addition, singular references do not exclude a plurality. Terms such as "a," "an," "first," "second," etc. do not exclude a plurality.

[0053] These and other aspects, features and advantages of the present invention will become apparent and elucidated from the following description of embodiments of the invention, which proceeds with reference to the accompanying drawings. [Brief description of the drawings]

[0054] [Figure 1] FIG. 1 shows a schematic flow path between the scrubber and the electrolytic cell. [Diagram 2] FIG. 2 shows a process scheme of a system for scrubbing flue gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Referring to FIG. 1, a schematic overview of a system 100 according to an embodiment is shown, comprising a scrubber unit 200 and a regeneration unit 300. Therein, a method for scrubbing gases, such as flue gas or exhaust gas, containing carbon dioxide CO2 is shown. These gases enter the scrubber through a scrubber inlet 213. To deplete the carbon dioxide CO2 from the flue gas, the scrubbing method can be described as follows: The gas is scrubbed in the scrubber 210 in a countercurrent manner with a first alkaline aqueous scrubbing liquid to remove the carbon dioxide CO2 and hydrogen carbonate HCO3. - and / or carbonate CO3 2- Dissolved bicarbonate HCO3 in the first alkaline aqueous wash. - and / or carbonate CO3 2- The result is a first spent aqueous cleaning solution comprising:

[0056] The first used aqueous cleaning liquid has a pH of about 7 to about 9 when it exits the outlet 211'' for withdrawing the used aqueous cleaning liquid from the scrubber 210.

[0057] The first spent aqueous wash solution is fed to the anode compartment 313 of the electrolysis cell for regeneration of the solution.

[0058] Besides the anode compartment 313, the electrolysis cell 310 also has a cathode compartment 312. The anode compartment 313 and the cathode compartment 312 are separated by a membrane 311. This membrane 311 may be a semi-permeable membrane, being permeable to cations but essentially impermeable to anions. The membrane is therefore a cation exchange membrane. In the cathode compartment 312, electrolysis increases the hydroxide concentration of the first used aqueous cleaning solution. In the anode compartment 313, electrolysis removes bicarbonate HCO3 from the first used aqueous cleaning solution by lowering the pH value and releasing gaseous carbon dioxide. - and carbonate CO3 2-The outlet 211'' for used aqueous cleaning liquid of the scrubber 210 is in flow communication with an inlet 313' for used aqueous cleaning liquid of the anode chamber 313. Furthermore, the outlet 312'' for regenerated aqueous cleaning liquid of the cathode chamber 312 is in flow communication with an inlet 212' for alkaline aqueous cleaning liquid of the scrubber 210.

[0059] The first used aqueous cleaning solution is electrolyzed in the cathode chamber 312 to produce gaseous hydrogen H2 and dissolved hydroxide ions OH - , and in the anode chamber 313, a gaseous mixture of oxygen O2 and carbon dioxide CO2 is generated. This is indicated in FIG. 1 by the upward arrows from the cathode outlet 312'' and the anode outlet 313'', respectively. Gaseous hydrogen H2 and dissolved hydroxide ions OH - is withdrawn from the cathode chamber 312 and a gaseous mixture of oxygen O2 and carbon dioxide CO2 is withdrawn from the anode chamber 313. For example, the hydrogen H2 can be used in downstream processes (not shown), such as fuel or methanol production. The regenerated alkaline aqueous wash solution from the cathode chamber 312 is then recycled to the scrubber 210 via an inlet 212' for receiving the alkaline aqueous wash solution. The carbon dioxide CO2-depleted gas then exits the scrubber 210 via a scrubber outlet 214.

[0060] In Fig. 2, a detailed view of the system 100 described in relation to Fig. 1 is shown. The system is separated into two parts: a scrubber unit 200 and a regeneration unit 300. For better understanding, the scrubber unit 200 and the regeneration unit 300 will now be described separately. Alternatively, the scrubber unit 200 and the regeneration unit 300 can be operated independently.

[0061] As shown in FIG. 2, the gaseous mixture S of oxygen O 2 and carbon dioxide CO 2 withdrawn from the anode chamber 313 is fed to a first compression unit 330 .

[0062] This means that when the system 100 is operating, the oxygen O2 and carbon dioxide CO2 leaving the first compression unit 330 are separated in the gas separator 340. The first gas separator 340 and the compression unit 330 can be integral, but are shown in the drawings as individual units.

[0063] In this case, the composition is typically about 75% CO2 and 25% O2. They can be compressed, for example, at about 50 bar at 10° C., where the carbon dioxide CO2 is liquefied and the oxygen O2 is still in the gas phase. The advantage of keeping the CO2 in the liquid phase is that it is practical during transportation.

[0064] A separator 340 is downstream of the compressor 330 and separates the first stream S1 of liquefied carbon dioxide from a second stream S2 containing oxygen and small amounts of carbon dioxide. The second stream, i.e. the oxygen in the second stream separated from the liquefied carbon dioxide or compressed and cooled so-called "off-gas", contains less than 30% carbon dioxide, or preferably less than 25% carbon dioxide. Typically the second stream contains 5-25% carbon dioxide.

[0065] The pH of the first spent aqueous liquid, prior to the introduction of the second stream of gas, may be in the range of 8 to 11. By introducing the second stream S2 into the first spent aqueous liquid, the carbon loading of said spent aqueous liquid is increased by at least 2%, preferably at least 4%, more preferably at least 5%, or by 2 to 10%, or by 3 to 7%, or by 4 to 6%.

[0066] By introducing a second stream S2 of cooled and compressed off-gas into the first spent aqueous cleaning liquid, the pH of the liquid can be increased (or "boosted") to a pH value above 10, which provides a more efficient electrolysis process.

[0067] Furthermore, by increasing the carbon loading, the amount of carbon dioxide in the gaseous mixture withdrawn from the electrolytic cell can be increased, which reduces the energy required to compress the gaseous mixture.

[0068] The off-gas, in one alternative embodiment, can be fed to a second compressor unit 395 where it is further compressed and cooled into a second stream S2', which is indicated by the dashed arrow in FIG. 2.

[0069] The separation unit 340 is in fluid connection with the first stream of used aqueous cleaning liquid coming from the scrubber outlet 211''.

[0070] At least a portion of the first spent aqueous cleaning liquid may be fed to a tank or vessel 400 suitable for pressurization into which a second stream S2 or S2′ of cooled and compressed off-gas comprising oxygen containing less than 30% CO2 is fed simultaneously during operation of the scrubbing and / or regeneration system. In this case, the vessel 400 serves as a mixing zone for mixing the spent aqueous liquid with the compressed and cooled second off-gas.

[0071] The tank or vessel 400 is further in flow communication with the anode chamber 313 of the electrolysis cell 310 via the anode inlet 313', which is supplied with the pressurized first spent aqueous cleaning liquid. The higher partial pressure of the cold compressed second gas will improve the uptake of CO2 into the liquid, and the first spent aqueous cleaning liquid will absorb CO2 from the off-gas and at the same time be pressurized before being introduced into the anode chamber. Oxygen from the second stream can be vented out of the vessel 400. It is important to remove oxygen before the first spent aqueous liquid enters the electrolysis cell, as otherwise it will be enriched in oxygen in the electrolysis cell, with the effect, among other things, of increasing the energy required to compress the gaseous mixture leaving the anode chamber. The liquid leaving the pressurization vessel 400 will also be pressurized, which means that the electrolysis cell will be operated at an increased pressure, which will improve the energy efficiency of the electrolysis or electrolysis cell system. Furthermore, drawing gases (hydrogen and CO2 / O2) from the electrolyser system under pressurized conditions has the advantage that less energy is required for the CO2 / O2 separation and hydrogen pressurization units, since the starting pressure for these units operation is higher than ambient pressure.

[0072] In one alternative, not shown in the drawings, a portion of the first spent aqueous cleaning solution is fed to the vessel 400 and a second portion is fed directly to the anode chamber 313 of the electrolysis cell 310 .

[0073] The compressor unit and gas separator 340, or according to an alternative embodiment, the second compressor / separator 395, may be in flow connection with the inlet section of the anode chamber. This means that the inlet section acts as a mixing zone for the spent washing liquid and the second compressed and cooled second stream S2 or S2' of off-gas. The mixing zone may be realized by injecting a second gas into the spent washing liquid stream or feed just before introduction into the anode chamber, where oxygen from the off-gas is also exhausted.

[0074] The mixing or mixing zone may also be immediately after the first used aqueous cleaning liquor exits the scrubber.

[0075] Referring to FIG. 2, the scrubber apparatus 200 includes a scrubber 210 having an inlet 211′ for receiving alkaline aqueous cleaning solution from a first buffer tank (not shown) and an outlet 211″ for withdrawing used aqueous cleaning solution and supplying it to an inlet 313′ for used aqueous cleaning solution in the anode chamber 313.

[0076] According to the illustration of Figure 1, the flue gas enters the scrubber 210 via the scrubber inlet 213. The scrubbing then takes place in two stages. The first stage takes place in a first absorber and the second stage takes place in a second absorber. The scrubbing takes place in a countercurrent manner, with the second absorber being located downstream of the first absorber.

[0077] When the scrubber apparatus 200 is located separately from the regeneration apparatus 300, such as in a vehicle, the regeneration apparatus 300, such as a charging station or vehicle depot, may also be provided with a third buffer tank and a fourth buffer tank, which are not shown in the figure.

[0078] Reference is now made to the regeneration apparatus 300. In addition to the electrolysis cell 310 and its components previously described in relation to FIG. 1, the regeneration apparatus 300 further comprises a compressor unit 320 for compressing the hydrogen gas withdrawn from the cathode chamber 312. Furthermore, the regeneration apparatus 300 further comprises a first compressor unit 330 for compressing the oxygen and carbon dioxide withdrawn from the anode chamber. Furthermore, the regeneration apparatus 300 also comprises a gas separator (not shown) for separating the oxygen O2 and carbon dioxide CO2 withdrawn from the anode chamber 313 from the liquid. This gas separator 340 is arranged upstream of the compressor unit 330.

[0079] In an alternative embodiment, a second compression unit (and separator unit) 395 is disposed upstream of the gas separator 340, which is shown as a dashed arrow. This second compression unit 395 may also be in fluid connection with the first spent aqueous washing liquid stream. To further explain the relationship between the scrubber apparatus 200 and the regenerator apparatus 300, the following explanation is provided. The regenerated alkaline aqueous washing liquid withdrawn from the cathode chamber 312 of the electrolytic cell 310 is supplied to the scrubber apparatus as an alkaline aqueous washing liquid. The washing process may comprise several washing steps, and the regenerated washing liquid may be supplied to one or more of these steps.

[0080] The pH of the first alkaline aqueous spent wash liquor is typically about 8 to 11. By adding the second stream S2 to the spent wash liquor, the carbon loading of the liquor is increased, which may result in a decrease in the pH level, where this decrease may be slight.

[0081] It should be noted that the electrolytic cell may be sensitive to impurities in the fluids flowing through the anode and cathode chambers. Therefore, there may also be a separate cleaning unit (not shown) that serves to remove impurities, such as, for example, nitrogen oxides NOx and sulfur oxides SOx, from the used aqueous cleaning solution before it enters the electrolytic cell 310. As an example, the cleaning unit may include a filter to remove particulate matter.

[0082] 1-2, it should be noted that the direction of the arrows corresponds to the direction of flow of the fluid circulating in the system 100. Additionally, the arrowed lines indicate fluid or flow communication between elements of the system.

[0083] <Chemical Process> The chemical process occurring in the system 100 can be divided into two distinct parts: carbon capture and electrochemical regeneration. The overall reaction is the electrochemical decomposition of water into oxygen and hydrogen according to the following equation: 2×H2O → O2 + 2×H2 This chemical reaction is balanced throughout the process capturing 4× CO2 molecules.

[0084] <Scrubba> In essence, carbon is captured in the scrubber 210 by dissolving carbon dioxide in the alkaline aqueous cleaning solution. This reaction occurs automatically according to the following equation: 4×OH - +4×CO2→4HCO3 -

[0085] The solvent is then regenerated using electrochemistry in the regenerator 300. In general, the electrochemical reaction can be divided into two parts: an anodic reaction and a cathodic reaction. These reactions are described below.

[0086] <Anode> In the anode chamber 313, O2 and CO2 were generated in two different steps. First, at the anode, 4H + Then, H + The pH value of the solvent was decreased and CO2 was released. At the same time, O2 was generated at the anode and the two gases were mixed in a ratio of CO2 to O2 of 4:1. The overall reaction in the anode chamber 313 is as follows: 4×HCO3 - →O2+4×CO2+2×H2O+4e - The reaction at the anode is as follows: 2×H2O→O2+4×H + +4e - This drop in pH value is due to HCO3 - Shift the / CO2 equilibrium to the right, so that: 4×H + +4×HCO3 - →4×CO2+4×H2O This results in the release of gaseous CO2 from the solvent.

[0087] <Cathode> At the cathode, OH - This reaction generates useful H2 for downstream applications and also produces hydroxide ions (OH - The cathode chamber reaction 312 is as follows: 4×H2O+4 - →2×H2+4×OH -

[0088] <Cleaning solution> Ethanolamine (MEA) is an amine used for carbon capture in conventional scrubbers. It has been suggested that MEA may act as an accelerator in the process of scrubbing, for example, flue gas. MEA is known to actually capture CO2 faster than hydroxide solutions. The envisioned idea was therefore to combine the carbon capture capabilities of MEA with the electrochemical properties of hydroxide solutions. However, experimental testing has shown that MEA unfortunately behaves undesirably in electrochemical cells. MEA appears to be reduced at the cathode, which reduces the carbon capture capabilities of the solvent, which is highly undesirable. Therefore, in the system 100 disclosed herein, it is preferred to use a metal hydroxide, for example potassium or sodium hydroxide.

[0089] <Required power> The electrochemical reaction in the electrolysis cell 310 requires power. The actual power consumption will depend on the technological implementation of the process of the system 100. Assuming 100% efficiency, the minimum current required for the process can be calculated using Faraday's law of thermodynamics: I=mFz / tM. The current can be calculated using the parameters listed in Table 1 below.

[0090] [Table 1]

[0091] Therefore, the current is I = 1.09 x 10 9 A. Assuming a minimum voltage of 2V, the theoretical minimum power consumption for 1 tonne of CO2 is: P min =2V×1.09×10 9 A = 2.18 × 109J = 2.18GJ

[0092] Higher energy consumption is expected for the actual chemical reactions. As suggested by the empirical model, the final power consumption for CO2 capture and solvent regeneration is predicted to be 5.88 GJ per ton of CO2. The process regenerates the solvent and produces H2 at the cathode 312 and a mixture of CO2 and O2 at the anode.

[0093] Separation of CO2 and O2 from the first gas separator 340 requires additional energy. This separation can be performed, for example, at cryogenic temperatures. The energy consumption of cryogenically separated CO2 from CH4 has been studied in the literature for biogas purposes. In the case of cryogenic separation, CO2 is removed by cooling, so CH4 and O2 have similar physio-chemical properties. The energy consumption for separation of O2 and CO2 in the first gas separator 340 is expected to be 1.4±0.4 MJ per kg of CO2.

[0094] CO2 and H2 are typically produced in a 2:1 ratio. If the downstream application is methanol production, then the preferred stoichiometric ratio is 1:3, and additional H2 is required for the process. Commercial electrolysis equipment produces H2 with an energy consumption of 55 kWh / kg. Thus, for one tonne of CO2, the required amount of H2 is (m co2 M co2)×3=68182 mol, which is equal to 68182 mol×2 g / mol×55 kWh / kg=7500 kWh=26.98 GJ. The carbon capture and regeneration process produces the equivalent of 4.5 GJ of H2, therefore the remaining energy requirement for H2 production is 26.98 GJ-4.50 GJ=22.48 GJ.

[0095] The power consumption of the carbon capture process is mainly determined by the electrochemical cell. The purification of CO2 requires additional energy. Since CO2 needs to be liquefied for transporting away from the site, the energy consumption for compressing CO2 is required in all carbon capture plants. Table 2 below is an example showing the compression of CO2 in pure form as a base case (meaning a starting pressure of 1 bar) compared to the compression of a CO2 / O2 mixture at starting pressures of 1 bar and 3 bar. The table shows that already at a starting pressure of 3 bar the energy consumption for liquefying the captured CO2 is similar to the base case. Operating the electrolyser unit at pressures above 3 bar would give an advantage to the liquefaction of CO2 compared to the base case.

[0096] [Table 2]

[0097] [Experimental section] <Example 1> In the following, the CO2 capture from a 10 MW heat and power plant from biomass is presented for three process steps: "scrubber", "regeneration" and "separation", see table 3. Overall, the process requires a large amount of electrical energy. The electrification of the carbon capture process is eagerly anticipated and is entirely new, so a large amount of electrical energy is positive. Part of the energy can be recovered as heat for district heating.

[0098] [Table 3]

[0099] <Example 2> Laboratory tests were conducted to verify the applicability of the process using the system 100 described herein.

[0100] For the laboratory tests, a standard electrolysis cell from EC Electrocell, model Electro MP Cell, was used. The electrolysis cell was provided with a Nafion 117 membrane. In operating the cell, a 1.5 M KHCO3 solution was circulated across the anode side from a combined degassing / circulation tank. The liquid was circulated at 1.5 L / min. Similarly, a 1.5 M KOH solution was circulated across the cathode side from a combined degassing / circulation tank. The liquid was circulated at 1.5 L / min. Standard flow meters and laboratory pumps were used. Gas flow from the degassing tank was measured by an Aalborg GFM gas flow meter. The CO2 content was measured using a Guardian NG from Edinburgh Sensors. A standard heating plate was used to keep the liquid at a constant temperature of 40 degrees Celsius during the experiments. The pH and temperature were measured in the circulation tank using a standard online pH meter and thermometer. The current density applied to the electrolysis cell was measured using a standard power converter at 1-4 kA / m 2 The results were varied between 0.01 and 0.1.

Claims

1. A gas containing carbon dioxide is extracted from the gas by extracting carbon dioxide (CO ２ 5. A method for washing to dramatically reduce the amount of fluoride in a liquid, comprising the steps of: - scrubbing the gas in a scrubber (210) with a first alkaline aqueous scrubbing liquid to remove carbon dioxide (CO ２ ) to hydrogen carbonate (HCO ３ － ) and / or as carbonate (CO ３ ２－ ) in the first alkaline aqueous wash, resulting in the formation of bicarbonate (HCO ３ － ) and / or carbonate (CO ３ ２－ providing a first used aqueous cleaning solution comprising: - supplying said first used aqueous cleaning solution to an electrolysis cell (310) comprising an anode compartment (313) and a cathode compartment (312); regenerating the first used aqueous cleaning solution in the electrolysis cell (310) by electrolysis and deriving bicarbonate (HCO3) from the first used aqueous cleaning solution in the anode chamber (313); ３ － ) and carbonate (CO ３ ２－ ) in the cathode chamber (312) and oxygen and carbon dioxide (CO ) in the anode chamber (313) by electrolysis. ２ ) and generating a gaseous mixture with - withdrawing the regenerated alkaline aqueous cleaning solution from the cathode chamber (312) and recycling it to the scrubber (210); where the carbon dioxide (CO ２ ) and / or oxygen (O ２ ) is compressed in a compression unit (330) into liquid carbon dioxide and compressed oxygen (O ２ ), Equipped with The method further comprises separating the liquid carbon dioxide from gaseous oxygen in a gas separator (340) to obtain a first stream (S1) comprising carbon dioxide; and a second stream (S2) comprising oxygen containing less than 30% carbon dioxide, wherein the second stream (S2) is introduced into at least a portion of the first used aqueous cleaning solution prior to supplying the first used aqueous cleaning solution to the anode compartment of the electrolysis cell (310).

2. 2. The method of claim 1, wherein the gas to be carbon dioxide depleted is one of flue gas, exhaust gas, or ambient air.

3. 2. The method of claim 1, wherein a pH of the first spent aqueous washing solution is in the range of 8 to 11 prior to the introduction of the second stream of gas, and the introduction increases a carbon loading of the first spent aqueous washing solution by 2 to 10%, or 3 to 7%, or 4 to 6%.

4. 2. The method of claim 1, wherein the first spent aqueous washing solution is separated into at least two streams after leaving the scrubber, and the second stream (S2) of compressed gas comprising oxygen containing less than 30% carbon dioxide is introduced into at least one of these first spent aqueous washing solution streams, and at least another first spent aqueous washing solution stream is fed directly to the electrolytic cell.

5. 1. A system for scrubbing a gas, such as a flue gas or exhaust gas, containing carbon dioxide to deplete carbon dioxide from the flue gas, the system comprising: Carbon dioxide converted to hydrogen carbonate (HCO ３ － ) and / or as carbonate (CO ３ ２－ a scrubber unit (200) for scrubbing the gas with an alkaline aqueous scrubbing liquid for dissolving said gas in said alkaline aqueous scrubbing liquid as a scrubber unit (200); a regeneration device (300) for regenerating the used aqueous cleaning liquid by electrolysis; Equipped with the scrubber unit comprises a scrubber (210) having an inlet (213) for the gas to be scrubbed and an outlet (214) for the carbon dioxide depleted gas, the scrubber (210) further having an inlet (212') for receiving the alkaline aqueous scrubbing liquid and an outlet (211") for withdrawing the used aqueous scrubbing liquid, said regeneration device comprises an electrolysis cell (310) comprising an anode chamber (313) and a cathode chamber (312), said anode chamber (313) comprising an anode inlet (313') for receiving said used aqueous cleaning solution and an anode outlet (313") for withdrawing oxygen and carbon dioxide, said cathode chamber (312) comprising an outlet (312") for withdrawing regenerated aqueous cleaning solution and hydrogen, the outlet (211″) for used aqueous cleaning liquid of the scrubber (210) is in flow communication with the inlet (313′) for used aqueous cleaning liquid of the anode chamber (313), the outlet (312″) for regenerated aqueous cleaning liquid of the cathode chamber (312) is in flow communication with the inlet (212′) for alkaline aqueous cleaning liquid of the scrubber (210), and the regeneration device a first compressor unit (330) for compressing the oxygen and carbon dioxide withdrawn from said anode chamber (313), The playback device, a gas separator (340) for separating the oxygen and carbon dioxide withdrawn from said anode chamber (313) into a first stream (S1) of liquefied carbon dioxide stream and a second stream (S2) comprising compressed gaseous oxygen containing less than 30% carbon dioxide, characterized in that said gas separator (340) is in flow connection with at least a portion of the spent aqueous washing liquid.

6. 6. The system of claim 5, further comprising a mixing zone for introducing the compressed second stream (S2) into the used aqueous cleaning solution prior to or simultaneously with feeding the used aqueous cleaning solution to the electrolytic cell (310).

7. 7. The system of claim 5 or 6, further comprising a second compressor unit (395) for further compressing at least a portion of the second stream (S2) of gaseous oxygen containing less than 30% carbon dioxide.

8. 7. The system of claim 6, wherein the mixing zone comprises a vessel (400) adapted to be pressurized and arranged between the outlet (211") for the used aqueous cleaning liquid of the scrubber (210) and the inlet (313') for the used aqueous cleaning liquid of the anode chamber (313), the vessel being in flow communication with the gas separator (340) for separating oxygen and carbon dioxide and / or with the second compressor unit (395), as well as with the scrubber outlet and the anode inlet.

9. 7. The system of claim 6, wherein the mixing zone is disposed at the anode inlet (313'), and the gas separator (340) for separating oxygen and carbon dioxide and / or the second compressor unit are further in flow communication with the anode inlet (313').

10. Hydrogen carbonate (HCO), which is used in electrolysis to provide an alkaline aqueous cleaning solution ３ － ) and / or carbonate (CO ３ ２－ 1. A regeneration apparatus for regenerating a used aqueous cleaning solution comprising: a) a catalytic converter for catalytic converter (300) for catalytic converter (300) comprising an electrolysis cell (310) comprising an anode chamber (313) and a cathode chamber (312) separated by a membrane 311, wherein the anode chamber (313) comprises an anode inlet (313') for receiving the used aqueous cleaning solution and an anode outlet (313") for withdrawing oxygen and carbon dioxide, and wherein the cathode chamber (312) comprises an outlet (312") for withdrawing regenerated aqueous cleaning solution and hydrogen, the regeneration apparatus comprising: a first compressor unit (330) for compressing the oxygen and carbon dioxide withdrawn from said anode chamber (313); a gas separator (340) for separating the oxygen and carbon dioxide withdrawn from said anode chamber (313) into a first stream (S1) of liquefied carbon dioxide and a second stream (S2) of gaseous oxygen containing less than 30% carbon dioxide; Further comprising: A regeneration apparatus, characterized in that said gas separator (340) is in flow connection with said first stream of spent aqueous wash liquid.

11. 11. The regeneration apparatus of claim 10, further comprising a mixing zone for introducing the compressed second stream (S2) into the used aqueous washing solution prior to or simultaneously with feeding the used aqueous washing solution to the electrolytic cell (310).

12. 12. The regenerator of claim 11, further comprising a second compressor unit (395) for further compressing the second stream (S2) comprising gaseous oxygen containing less than 30% carbon dioxide.

13. 12. The regeneration apparatus according to claim 11, wherein the mixing zone comprises a vessel (400) adapted to be pressurized and arranged between an outlet (211'') for the used aqueous cleaning liquid of the scrubber (210) and the inlet (313') for the used aqueous cleaning liquid of the anode chamber (313), the vessel (400) being in flow communication with the gas separator (340) for separating oxygen and carbon dioxide and / or with the second compressor unit (395), as well as with the scrubber outlet and the anode inlet.

14. 12. The regenerator of claim 11, wherein the mixing zone is disposed at the inlet (313') of the anode chamber, and the gas separator (340) for separating oxygen and carbon dioxide and / or the second compressor unit (395) are further in flow communication with the anode inlet (313').

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