Method and system for removing oxygen from a carbon dioxide stream

Abstract

The method includes compressing a gaseous oxygen-containing carbon dioxide stream and increasing its temperature by compression, and feeding the compressed and heated oxygen-containing carbon dioxide stream through an oxygen removal package (13) to remove oxygen, thereby utilizing the temperature achieved by compression to drive the oxygen removal reaction in the oxygen removal package (13). The oxygen-depleted carbon dioxide stream is then cooled for further processing. A system for carrying out the method outlined above is further disclosed.

Description

[Technical field]

[0001] The present disclosure relates to methods and systems for enhanced oxygen removal from a carbon dioxide stream. [Background technology]

[0002] Carbon dioxide is produced by several human industrial activities, notably the burning of fossil fuels to produce electricity. Carbon dioxide is one of the greenhouse gases responsible for the climate changes associated with global warming.

[0003] In an attempt to reduce the adverse environmental impact of greenhouse gases, systems and methods for carbon capture and storage (CCS) have been developed to reduce CO2 emissions. The captured carbon dioxide is typically transported in pipelines or tanks. It must be treated to meet transportation regulations and compressed before it can be used for pipeline transportation or liquefaction and transportation in tanks. To avoid corrosion during transportation, water and other impurities such as oxygen must be removed from the carbon dioxide. For this purpose, oxygen removal packages are used. In known systems, the oxygen-containing carbon dioxide stream is treated under heating conditions in the oxygen removal package. Heating requires a large amount of energy, which increases the energy consumption of the overall process and makes it inefficient. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, methods and systems aimed at reducing the amount of energy required to remove oxygen from carbon dioxide streams, making the process more effective and efficient, would be welcomed in the art.

[0005] According to one aspect, a method for removing oxygen from a gas stream of carbon dioxide is disclosed herein.

[0006] In an embodiment disclosed herein, the method includes compressing a gaseous oxygen-containing carbon dioxide stream and heating the carbon dioxide stream to a reaction temperature by compression. The required reaction temperature is achieved by the effect of converting mechanical energy to heat in the carbon dioxide compressor, without the need to provide additional energy, for example from an electric heater. This represents a significant energy saving.

[0007] The method further comprises providing a high pressure hydrogen stream produced by a high-pressure electrolyser. As understood herein, a "high pressure electrolyser" is an electrolyser adapted to produce hydrogen at a pressure of 20 barg or more, and in some embodiments 30 barg or more. As understood herein, "high pressure hydrogen" produced by electrolysis is hydrogen at a pressure of 20 barg or more, and in some embodiments 30 barg or more. The use of a high pressure electrolyser provides further energy savings. High pressure electrolysers may include, for example, alkaline electrolysers or polymer electrolyte membrane (PEM) electrolysers.

[0008] The high pressure hydrogen produced by the high pressure electrolyser and the compressed and heated oxygen-containing carbon dioxide stream are fed to an oxygen removal package, e.g., a catalytic oxidation (CATOX) reactor, where the hydrogen reacts with oxygen contained in the oxygen-containing carbon dioxide stream to remove oxygen from the oxygen-containing carbon dioxide stream. The resulting substantially oxygen-free carbon dioxide stream may be cooled prior to further processing, such as cooling and liquefaction, for storage or transportation purposes.

[0009] In effect, the temperature of the oxygen-containing carbon dioxide stream achieved by compression is used to drive the oxygen removal reaction in the oxygen removal package.

[0010] In some embodiments, the oxygen removal package is adapted to operate at a temperature of no more than 150° C., or no more than 120° C. For example, the oxygen removal package may oerate from 80° C. to 150° C., or from 80° C. to 120° C., such as from 100° C. to 120° C. The oxygen removal package may further operate at a pressure of from 20 to 60 barg, such as from 20 to 55 barg, or from 20 to 45 barg.

[0011] Intercooled compressors conventionally used to compress oxygen-containing carbon dioxide streams, for example, achieve an output temperature of about 120° C. Thus, the methods disclosed herein can be practiced using conventional intercooled compressors, without the need to provide additional heat energy to the compressed oxygen-containing carbon dioxide stream and without the need to remove the intercooler, thereby maintaining high compression efficiency.

[0012] The oxygen-containing carbon dioxide stream may be delivered to the catalytic oxidation reactor from the delivery side of the compressor or compressor train, i.e. after the final pressure of the carbon dioxide stream has been reached. However, the option of treating the oxygen-containing carbon dioxide stream before the final pressure is reached is not excluded. That is, the oxygen-containing carbon dioxide stream may be compressed to some extent, treated in the catalytic oxidation reactor for oxygen removal, and then further compressed to the final pressure required for transport, storage and / or liquefaction.

[0013] For example, an oxygen-containing carbon dioxide stream may be compressed to some extent in one or more compressor stages or compressors, optionally with intercoolers, arranged in sequence, and then processed through a catalytic oxidation reactor, where the oxygen-free carbon dioxide stream from the catalytic oxidation reactor may be further compressed to the required final pressure.

[0014] In some embodiments, the hydrogen produced by high pressure electrolysis can be further compressed to a suitable pressure higher than the hydrogen delivery pressure of the high pressure electrolyzer, and this hydrogen can be further heated to a suitable temperature before being fed to the catalytic oxidation reactor.

[0015] In some embodiments, the compression of hydrogen can be performed in a static compression unit, ie, a device that has no moving mechanical parts.

[0016] In some embodiments, the hydrogen produced by the high pressure electrolyzer can be compressed by a metal hydride absorption and desorption process, the final temperature and pressure of the compressed hydrogen delivered by the metal hydride absorption and desorption process can be suitable for direct feed to a catalytic oxidation reactor.

[0017] If, especially in transient conditions, the heating of the hydrogen by the metal hydride absorption and desorption processes is insufficient and the catalytic oxidation reactor requires additional heat energy, the latter may be provided by a heater, for example an electric heater. An external heater can be used, especially during start-up.

[0018] According to another aspect, a system for removing oxygen from an oxygen-containing carbon dioxide stream is disclosed herein. The system comprises a carbon dioxide compressor and an oxygen removal package, such as a catalytic oxidation reactor, fluidly coupled to the carbon dioxide compressor. The system further comprises a high pressure electrolyser adapted to produce hydrogen at high pressure, i.e., 20 barg or higher, e.g., 30 barg or higher. The electrolyser is fluidly coupled to the catalytic oxidation reactor and adapted to supply hydrogen to the catalytic oxidation reactor. The catalytic oxidation reactor is adapted to cause an oxidation reaction of hydrogen with oxygen contained in the compressed carbon dioxide stream. The carbon dioxide compressor can be an intercooled compressor. The carbon dioxide compressor is adapted to deliver a compressed stream of oxygen-containing carbon dioxide at a temperature adapted to react with hydrogen in the oxygen removal package, e.g., at a temperature between 80°C and 150°C, or between 80°C and 120°C, e.g., between 100°C and 120°C.

[0019] In use, the oxygen removal package is adapted to receive an oxygen-containing carbon dioxide stream at a reaction temperature, which is achieved by compression in the carbon dioxide compressor, suitable for reacting oxygen with hydrogen produced by the high pressure electrolyser.

[0020] The system may further include a cooler downstream of the catalytic oxidation reactor, the cooler adapted to cool the carbon dioxide stream after oxygen removal by the catalytic oxidation reactor.

[0021] The system may further include a metal hydride compression and storage unit adapted to further compress the hydrogen produced by the high pressure electrolyzer. The metal hydride compression unit also increases the temperature of the hydrogen.

[0022] Further features and embodiments of the methods and systems according to the present disclosure are set forth in the following description, with reference to the accompanying drawings, and in the appended claims. [Brief description of the drawings]

[0023] Reference will now be made briefly to the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic diagram of a system according to the present disclosure. [Diagram 2] FIG. 2 is a flow chart summarizing a method according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Briefly, prior to cooling and transport, a gaseous stream of oxygen-containing carbon dioxide is processed in a compressor. The temperature of the carbon dioxide stream is increased by compression. The heat thus generated is utilized to operate the oxygen removal package at a suitable operating temperature, eliminating the need for large amounts of external heat energy supplies. This results in an efficient system that reduces overall power consumption and improves the efficiency of the process.

[0025] Referring now to the drawings, FIG. 1 is a schematic diagram of a system 1 for treating a gas stream of oxygen-containing carbon dioxide from which oxygen is to be removed prior to transport, storage or other manipulation.

[0026] The oxygen-containing carbon dioxide stream is delivered along inlet line 3, which may be provided by any upstream facility (not shown), such as, for example, a chilled ammonia process system that recovers carbon dioxide from flue gas produced by a gas turbine. The system further comprises a first gas / water separator 5 in which water contained in the carbon dioxide stream flowing through inlet line 3 is removed.

[0027] The system 1 further comprises a carbon dioxide compressor 7. In practice, the carbon dioxide compressor 7 may include one or more compressors or compressor stages, which may be driven by one or more drivers 9 via one or more shafts 10. In the schematic diagram of Figure 1, the compressor 7 is shown as a two-stage compressor including a first compressor or compressor stage 7A and a second compressor or compressor stage 7B. An intercooler 11 may be provided between the first compressor or compressor stage 7A and the second compressor or compressor stage 7B.

[0028] The output side of the carbon dioxide compressor 7 is fluidly coupled to an oxygen removal package 13, which may include a catalytic oxidation reactor (abbreviated as CATOX) 14. In the oxygen removal package 13, oxygen is removed from the carbon dioxide stream by catalytically reacting the oxygen with a reactant gas, specifically hydrogen. In embodiments disclosed herein, the reactant gas is or includes hydrogen, which is delivered to the oxygen removal package 13 by a hydrogen source, generally indicated at 15. One embodiment of a suitable hydrogen source is described below.

[0029] The oxidation reaction in catalytic oxidation reactor 13 is carried out at an oxidation pressure (also referred to herein as the reaction pressure) that is greater than ambient pressure, and at an oxidation temperature (also referred to herein as the reaction temperature) that is greater than ambient temperature.

[0030] When the reaction gas is hydrogen, the oxidation pressure may be 20 to 60 barg, for example, 20 to 55 barg, or 20 to 45 barg. The oxidation temperature may be greater than 80°C, for example, 80°C to 150°C, or 80°C to 120°C, for example, 100°C to 120°C.

[0031] In some embodiments, the carbon dioxide compressor 7 is configured and controlled to deliver a compressed oxygen-containing carbon dioxide stream that is at the required oxidation pressure and temperature when it enters the catalytic oxidation reactor 14 without the need for external heating (i.e., no need to provide any further thermal energy to the carbon dioxide stream). For example, the oxygen-containing carbon dioxide stream may be at a pressure of 20-60 barg, e.g., 20-55 barg, or 20-45 barg. The temperature of the oxygen-containing carbon dioxide stream may be comprised between 80° C. and 150° C., or between 80° C. and 120° C., e.g., between 100° C. and 120° C. Standard intercooled centrifugal compressor systems can be used to achieve these temperature and pressure ranges.

[0032] 1, the hydrogen source 15 includes an electrolyzer 17 that is powered by electricity from a power grid 19. In some embodiments, the electrolyzer 17 is a high-pressure electrolyzer.

[0033] The hydrogen produced by the electrolyser may be at a pressure of 20 barg or more, for example 30 barg or more.

[0034] Power for the electrolyser can be provided by a power generation system 21 using renewable energy sources. In the embodiment of Figure 1, the power generation system 21 includes a solar power panel 23 and an inverter 25 for converting solar power to AC power.

[0035] Power is delivered to the power grid 19 and supplied to the electrolyzer 17 via an AC / DC converter and possibly other utilities as described below. In other embodiments, DC power generated by photovoltaic panels may be used directly to power the electrolyzer without prior DC / AC conversion.

[0036] Other renewable energy sources may be used, such as wind power through wind farms etc. The use of power generating equipment using water, steam or gas turbines or combinations thereof, possibly in combination with renewable energy sources, is not excluded.

[0037] The pressure and temperature of the hydrogen produced in the electrolyser 17 may be insufficient for reaction with oxygen in the catalytic oxidation reactor 13. For example, the electrolyser 17 may be a high pressure electrolyser generating hydrogen at 20 barg or more, such as 30 barg or more. The outlet hydrogen temperature may be between 50°C and 80°C, such as between about 65°C and 75°C.

[0038] If the pressure and / or temperature of the hydrogen produced by the electrolyser 17 is insufficient, devices for increasing the hydrogen pressure and / or the hydrogen temperature can be used.

[0039] In some embodiments, a reciprocating compressor or a speed type compressor, possibly in combination with a heater such as an electric heater, can be used to increase the pressure and temperature of the hydrogen.

[0040] However, in some embodiments, a metal hydride absorption and desorption process using a metal hydride compression and storage unit 31 is used to increase the pressure and temperature of the hydrogen delivered by the electrolyzer 17.

[0041] As known from the hydrogen processing and storage art, a metal hydride compression and storage unit is a static compression system that breaks down hydrogen molecules (H2) into hydrogen atoms (H) and absorbs the hydrogen atoms (H) into the interstitial spaces of a metal alloy. The thermodynamic properties of the metal hydride material are used to compress and store the hydrogen until it is later released (ejected) at high pressure. While the absorption process releases heat, the subsequent release stage requires heating to release the hydrogen from the metal alloy at a pressure higher than the initial pressure at which the hydrogen was delivered to the metal alloy for absorption. Further details regarding the application of hydrides for hydrogen storage and compression are described in Jose Bellosta von Colbe, et al., "Application of Hydrides in Hydrogen Storage and Compression: Achievements, Outlook and Perspectives," International Journal of Hydrogen Energy 44 (2019) 7780-7808, available online at www.sciencedirect.com. A hydrogen storage system using metal hydrides is disclosed, for example, in EP 3726124.

[0042] Heat to operate the metal hydride compression and storage unit 31 may be provided by electrical power from the power grid 19 via a heater 33, if required.

[0043] The oxygen removal package 11 may be fluidly coupled to a cooler 37 via a line delivering the oxygen-free carbon dioxide stream from the oxygen removal package 11, which cooler 37 removes heat from the carbon dioxide stream. The outlet side of the cooler 37 may be fluidly coupled to a second gas / water separator 39. The water outlet of the gas / water separator 39 may be fluidly coupled to the first gas / water separator 5 via a return line 41. The gas outlet of the second gas / water separator 39 may be fluidly coupled to a dryer 45 via a line 43. The water from the dryer 45 may be returned to the first gas / water separator 5 via a return line 47, and the cooled and dried carbon dioxide stream may be further delivered to a processing unit 48, for example a pipeline or a liquefaction unit.

[0044] The above-described system can efficiently process oxygen-containing carbon dioxide streams and can reduce the amount of energy required to operate the oxygen removal package since the carbon dioxide stream is heated by compression by the carbon dioxide compressor 7. A static hydrogen compression system using a metal hydride compression and storage unit 31 optimizes the hydrogen compression and heating process since the heat generated during hydrogen absorption in the metal alloy is utilized during the release of hydrogen at higher pressures from the metal alloy.

[0045] During operation at steady state operating conditions, the temperature of the catalytic oxidation reactor 13 is sufficient to prevent water vapor contained in the carbon dioxide stream from condensing in the catalytic oxidation reactor and damaging the catalyst contained therein.

[0046] To avoid condensation of moisture in the catalytic oxidation reactor 13 during start-up, in some embodiments the catalytic oxidation reactor 13 may be equipped with a heater 51 adapted to pre-heat the reactor mass and the catalyst material. The heater 51 may be, for example, an electric heater and may be powered by the electrical grid 19.

[0047] The method for removing oxygen from a carbon dioxide stream implemented by system 1 is summarized in the flow chart of Figure 2. The flow chart shows the steps of compressing a gaseous oxygen-containing carbon dioxide stream by compressor 7 to increase the temperature (step 101), feeding the oxygen-containing carbon dioxide stream through catalytic oxidation reactor 13 at the required reaction temperature and pressure (step 102), feeding hydrogen from hydrogen source 15 to catalytic oxidation reactor 13 (step 103), oxidizing the hydrogen in catalytic oxidation reactor 13 by reaction with oxygen contained in the carbon dioxide stream (step 104), cooling the carbon dioxide in heat exchanger 37 (step 105), and finally removing water from the oxygen-free carbon dioxide stream (step 106).

[0048] Exemplary embodiments are disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various modifications, omissions, and additions may be made to what is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

Claims

1. 1. A method for removing oxygen from a gas stream of carbon dioxide, the method comprising: compressing a gaseous oxygen-containing carbon dioxide stream and heating said oxygen-containing carbon dioxide stream to an oxidation reaction temperature by compression; generating hydrogen in a high pressure electrolyser; providing the hydrogen and the compressed and heated oxygen-containing carbon dioxide stream to an oxygen removal package; removing oxygen from said oxygen-containing carbon dioxide stream by reacting hydrogen with oxygen from said oxygen-containing carbon dioxide stream in said oxygen removal package; and cooling said carbon dioxide stream discharged from said oxygen removal package.

2. The method of claim 1 , wherein the oxygen removal package comprises a catalytic oxidation reactor.

3. 3. The method of claim 1 or 2, wherein the hydrogen produced by the high pressure electrolyser is further compressed and heated upstream of the oxygen removal package.

4. 4. The method of claim 3, wherein the hydrogen is further compressed to an oxidation pressure and heated to an oxidation temperature by absorption and desorption by a metal hydride.

5. 5. A method according to any one of claims 1 to 4, wherein the oxygen-containing carbon dioxide stream is heated by compression to a temperature of from 80°C to 150°C, or from 80°C to 120°C, or from 100°C to 120°C, and the step of reacting hydrogen and oxygen in the oxygen removal package is carried out at a reaction temperature of from 80°C to 150°C, or from 80°C to 120°C, or from 100°C to 120°C.

6. A process as claimed in any one of the preceding claims, wherein the oxygen-containing carbon dioxide stream is supplied to the oxygen removal package at a pressure comprised between 20 barg and 60 barA, or between 20 barg and 55 barg.

7. A method according to any one of claims 1 to 6, wherein the step of compressing the gaseous oxygen-containing carbon dioxide stream is carried out in an intercooled compressor.

8. 1. A system for removing oxygen from a gaseous oxygen-containing carbon dioxide stream, the system comprising: A carbon dioxide compressor; an oxygen removal package fluidly coupled to the carbon dioxide compressor; a high pressure electrolyser adapted to supply hydrogen to the oxygen removal package; 1. The system, wherein, in use, the oxygen removal package is adapted to receive an oxygen-containing carbon dioxide stream from the carbon dioxide compressor, the carbon dioxide stream being at a reaction temperature and pressure established by compression in the carbon dioxide compressor, and hydrogen produced from the high pressure electrolyzer.

9. 10. The system of claim 8, further comprising a cooler downstream of the oxygen removal package adapted to receive the oxygen-removed carbon dioxide stream from the oxygen removal package.

10. 10. The system of claim 8 or 9, wherein the oxygen removal package comprises a catalytic oxidation reactor.

11. 11. The system of any one of claims 8 to 10, further comprising a metal hydride compression and storage unit adapted to receive hydrogen from the high pressure electrolyzer and supply compressed and heated hydrogen to the oxygen removal package.

12. 12. The system of claim 11, further comprising a heater for heating the metal hydride compression and storage unit, particularly during start-up.

13. A system according to any one of claims 8 to 12, wherein the oxygen removal package is adapted to operate at an oxidation pressure of from 20 to 60 barg, such as from 20 to 55 barg, or from 20 to 45 barg.

14. The system of any one of claims 8 to 12, wherein the oxygen removal package is adapted to operate at an oxidation temperature of from 80°C to 150°C, or from 100°C to 120°C.

15. The system of any one of claims 8 to 13, further comprising a heater for heating the oxygen removal package during start-up.

16. 16. The system of any one of claims 8 to 15, wherein the carbon dioxide compressor is an intercooled compressor including a first compressor stage, a second compressor stage, and an intercooler between the first compressor stage and the second compressor stage.

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