Electrolytic system

Abstract

This invention provides an electrolysis system that can efficiently utilize the oxygen generated at the air electrode. [Solution] The electrolysis system 100 comprises an electrolysis unit 2 having at least a fuel electrode 23, an air electrode 22, and an electrolyte 21 disposed between the fuel electrode 23 and the air electrode 22; a fuel gas supply unit 1 that supplies at least one of water vapor and carbon dioxide to the fuel electrode 23; a sweep gas supply unit 3 that supplies sweep gas mainly composed of carbon dioxide to the air electrode 22; an electrolysis gas discharge unit 4 that discharges electrolysis gas containing at least one of hydrogen and carbon monoxide produced at the fuel electrode 23; and an oxygen-enriched gas discharge unit 5 that discharges oxygen-enriched gas containing oxygen produced at the air electrode 22.

Description

Technical Field

[0001] The present invention relates to an electrolysis system.

Background Art

[0002] A method is known in which carbon dioxide and steam as raw materials are co-electrolyzed by a solid oxide electrolysis cell (SOEC) stack to produce carbon monoxide and hydrogen, and methane is produced from carbon monoxide and hydrogen in a methanation device provided in the subsequent stage (see, for example, Patent Document 1).

[0003] In the fuel electrode (cathode) of a solid oxide electrolysis cell stack, carbon monoxide and hydrogen are generated, and oxygen is generated in the air electrode (anode). The electrolysis system described in Patent Document 1 includes a pipe for supplying air to the air electrode. By supplying air as a sweep gas to the air electrode, relaxation of oxygen concentration polarization on the air electrode surface and suppression of oxidation corrosion of the high-temperature pipe by thinning the oxygen concentration on the outlet side are achieved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Oxygen is industrially used in a wide range of applications and is valuable. Therefore, it is desirable to effectively use the oxygen generated at the air electrode. However, since the oxygen discharged from the air electrode is mixed with air as a sweep gas, it is necessary to separate oxygen and air in order to use the oxygen. Separation of nitrogen and oxygen contained in air is performed by cryogenic separation or the like, but there are problems in efficiently using the oxygen generated at the air electrode because large-scale equipment is required and energy is required for separation.

[0006] This invention has been made in view of the above-mentioned problems, and its purpose is to provide an electrolysis system that can efficiently utilize oxygen generated at the air electrode. [Means for solving the problem]

[0007] The characteristic configuration of the electrolytic system according to the present invention is an electrolytic unit having at least a fuel electrode, an air electrode, and an electrolyte disposed between the fuel electrode and the air electrode, A fuel gas supply unit that supplies at least one of water vapor and carbon dioxide to the fuel electrode, A sweep gas supply unit that supplies a sweep gas mainly composed of carbon dioxide to the air electrode, An electrolytic gas discharge unit that discharges an electrolytic gas containing at least one of hydrogen and carbon monoxide produced at the fuel electrode, The distinguishing feature is the inclusion of an oxygen-enriched gas discharge unit that discharges oxygen-containing oxygen generated at the aforementioned air electrode.

[0008] In this configuration, since a sweep gas mainly composed of carbon dioxide is supplied to the air electrode, the oxygen-enriched gas discharged from the air electrode is mainly a mixture of carbon dioxide and oxygen. Because carbon dioxide has a larger molecular size relative to oxygen and different chemical properties compared to nitrogen, it is easily separated by membrane separation or chemical absorption methods, and the separation of oxygen from the oxygen-enriched gas is easier compared to the separation of nitrogen and oxygen. Therefore, with the electrolysis system according to this configuration, oxygen can be easily separated from the oxygen-enriched gas, and the oxygen generated at the air electrode can be utilized efficiently.

[0009] Another characteristic feature is that the carbon dioxide concentration of the sweep gas is 80% by volume or higher.

[0010] With this configuration, the carbon dioxide concentration of the sweep gas can be increased, allowing the oxygen-enriched gas to be mainly a mixture of oxygen and carbon dioxide, and high-concentration oxygen can be obtained by separating carbon dioxide from the oxygen-enriched gas.

[0011] Another characteristic feature is that the oxygen concentration of the oxygen-enriched gas is between 20% by volume and 50% by volume.

[0012] This configuration makes it possible to mitigate concentration polarization at the air electrode surface, suppress oxidative corrosion of piping and other components at the oxygen-enriched gas discharge section, and efficiently separate oxygen from the oxygen-enriched gas.

[0013] Another notable feature is the inclusion of a separation unit that separates oxygen from the oxygen-enriched gas discharged from the oxygen-enriched gas discharge unit.

[0014] With this configuration, oxygen can be separated from the oxygen-enriched gas by the separation unit, making it possible to continuously obtain oxygen in the electrolysis system.

[0015] Another characteristic feature is that the sweep gas includes the separated gas from which oxygen has been separated in the separation unit.

[0016] The separated gas, from which oxygen has been separated from the oxygen-enriched gas, is mainly composed of carbon dioxide. Therefore, with this configuration, the separated gas and the heat it contains can be reused, making it possible to reduce the energy required to heat the sweep gas.

[0017] Another characteristic feature is that the oxygen-enriched gas is used for oxygen combustion.

[0018] This configuration allows for the effective utilization of oxygen-enriched gas without the need to separate oxygen from it. Furthermore, it enables the recovery of high concentrations of carbon dioxide from the exhaust gas obtained through oxygen combustion.

[0019] Another characteristic feature is that the electrolyte is a solid oxide.

[0020] This configuration makes it possible to improve the energy efficiency of the electrolysis system.

[0021] As another characteristic configuration, the fuel gas supply unit supplies the steam and the carbon dioxide to the fuel electrode, the electrolysis unit performs co-electrolysis of the steam and the carbon dioxide, the electrolysis gas discharge unit discharges the electrolysis gas containing the hydrogen and the carbon monoxide generated at the fuel electrode.

[0022] According to this configuration, in an electrolysis system in which the electrolysis unit performs co-electrolysis of steam and carbon dioxide, it becomes possible to efficiently utilize the oxygen generated at the air electrode.

Brief Description of the Drawings

[0023] [Figure 1] It is a diagram showing a schematic configuration of an electrolysis system according to a first embodiment. [Figure 2] It is a diagram showing a schematic configuration of an electrolysis system according to a second embodiment. [Figure 3] It is a diagram showing a schematic configuration of an electrolysis system according to other embodiments.

Mode for Carrying Out the Invention

[0024] 〔First Embodiment〕 Hereinafter, an embodiment of an electrolysis system 100 according to the present invention will be described based on the drawings. However, it is not limited to the following embodiments, and various modifications are possible without departing from the gist thereof.

[0025] As shown in FIG. 1, an electrolysis system 100 according to the first embodiment includes a fuel gas supply unit 1, an electrolysis unit 2, a sweep gas supply unit 3, an electrolysis gas discharge unit 4, and an oxygen-enriched gas discharge unit 5.

[0026] 〔Fuel Gas Supply Unit〕 The fuel gas supply unit 1 includes a steam supply unit 11 that supplies steam to the electrolysis unit 2 and a carbon dioxide supply unit 12 that supplies carbon dioxide to the electrolysis unit 2. The steam supply unit 11 includes a steam supply passage 11a through which water or steam flows, a flow regulator 110 that adjusts the flow rate of steam, and an evaporator 111 for evaporating water. The steam supply passage 11a is preferably connected to an unshown water tank on the upstream side in the direction of water or steam flow (hereinafter, the upstream or downstream side in the direction of flow will be simply referred to as the upstream side or the downstream side), and is preferably connected to a confluence passage 13a on its downstream side. The flow regulator 110 and the evaporator 111 are preferably located on the steam supply passage 11a. In the evaporator 111, the heat source for evaporating water is not particularly limited, but if a methanation device is provided downstream of the electrolysis system 100, the heat generated by the methanation device may be used, or an electric heater or the like may be used. The flow regulator 110 is configured to constantly control the water vapor flow rate based on the ratio of the water vapor flow rate to the carbon dioxide flow rate calculated by a control unit (not shown) of the electrolysis system 100. Therefore, it is preferable that a measuring instrument (not shown) for measuring the water vapor flow rate be provided on the water vapor supply path 11a. The control unit consists of a microcontroller including a processor and semiconductor memory. The electrolysis system 100 is preferable to have a storage unit (not shown) for storing the water vapor flow rate measured by the measuring instrument.

[0027] The carbon dioxide supply unit 12 includes a carbon dioxide supply passage 12a through which carbon dioxide flows, and a flow regulator 120 that adjusts the flow rate of carbon dioxide. The carbon dioxide supply passage 12a is often connected to a carbon dioxide tank or carbon dioxide source (not shown) on its upstream side, and to a confluence passage 13a on its downstream side. The flow regulator 120 may be provided on the carbon dioxide supply passage 12a. The flow regulator 120 is capable of constantly controlling the flow rate of carbon dioxide based on the ratio of the flow rate of water vapor to the flow rate of carbon dioxide calculated by the control unit. Therefore, a measuring instrument (not shown) for measuring the flow rate of carbon dioxide is often provided on the carbon dioxide supply passage 12a, and the flow rate of carbon dioxide measured by the measuring instrument is preferably stored in a memory unit.

[0028] The carbon dioxide used as a raw material can be produced by any method, as long as it has a purity and properties that do not hinder the electrolytic reaction in the solid oxide electrolytic cell. It may be carbon dioxide recovered from combustion exhaust gas by known carbon dioxide recovery methods such as the amine absorption method, or it may be carbon dioxide recovered from biogas obtained by methane fermentation of organic matter.

[0029] If carbon dioxide contains sulfur, halogen compounds, siloxane compounds, heavy hydrocarbons, etc., these can cause deterioration of solid oxide type electrolytic cells, etc., so it is preferable to remove them before the reaction if necessary.

[0030] The water vapor supply channel 11a and the carbon dioxide supply channel 12a are connected to a confluence channel 13a that combines the water vapor and carbon dioxide. The confluence channel 13a is connected to the fuel electrode 23 of the solid oxide electrolytic cell provided in the electrolytic unit 2.

[0031] [Electrolytic part] The electrolytic unit 2 includes, for example, a solid oxide electrolysis cell (SOEC). The electrolytic unit 2 has at least an air electrode 22, a fuel electrode 23, and a solid electrolyte 21 (an example of an electrolyte) that is placed between the air electrode 22 and the fuel electrode 23 and conducts oxygen ions. Examples of solid electrolytes 21 include yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), ytterbia-stabilized zirconia (YbSZ), lanthanum gallate (LaSrGdMgO3, LSGM), etc.

[0032] A power supply unit 24 is connected to the air electrode 22 and the fuel electrode 23 to supply power to the air electrode 22 and the fuel electrode 23. The power supply unit 24 is configured to apply a positive potential to the air electrode 22 and a negative potential to the fuel electrode 23. The voltage applied to the air electrode 22 and the fuel electrode 23 should be approximately 1.0V to 1.3V. The electrolytic unit 2 may also be equipped with an ammeter (not shown) for measuring the electrolytic current value.

[0033] Electrolytic reactions are typically carried out at temperatures of around 600°C to 1000°C, preferably around 650°C to 850°C. When the electrolytic reaction temperature is within this range, the oxygen ion conductivity of the electrolyte material is ensured, and the electrode reaction occurs rapidly. By setting the voltage to approximately the theoretical electrolytic voltage, electrolysis can be continued, enabling highly efficient operation.

[0034] The electrolytic unit 2 generates a mixed gas (mixed fluid) consisting of an electrolytic gas containing hydrogen (H2) and carbon monoxide (CO) and an unelectrolyzed gas of water vapor and carbon dioxide from water (H2O) and carbon dioxide (CO2) through co-electrolysis. Co-electrolysis is a reaction in which equations (I) and (II) proceed simultaneously at the fuel electrode 23, as shown below. Oxygen ions produced by the co-electrolysis of water vapor and carbon dioxide at the air electrode 22 move through the solid electrolyte 21 due to the potential gradient and to the air electrode 22, where oxygen gas is generated according to equation (III). The combined electrolytic reaction is an endothermic reaction. <Fuel electrode> H2O + 2e - →H2+O 2- ...(I) CO2 + 2e - →CO+O 2- ...(II) <Air pole> 20 2- →O2+4e - ...(III)

[0035] [Sweep Gas Supply Department] The sweep gas supply unit 3 supplies a sweep gas mainly composed of carbon dioxide to the air electrode 22 in order to remove the oxygen generated by formula (III) from the air electrode 22. "Mainly composed of carbon dioxide" means that the sweep gas contains 50% or more by volume of carbon dioxide. The sweep gas preferably contains 60% or more by volume of carbon dioxide, more preferably 70% or more by volume, even more preferably 80% or more by volume, particularly preferably 90% or more by volume, and most preferably 99% or more by volume. The components other than carbon dioxide in the sweep gas are not particularly limited as long as they are not reducing gases such as hydrogen or carbon monoxide, and may be any. The components other than carbon dioxide in the sweep gas may be nitrogen, for example. As will be described in detail later, according to this embodiment, even if the sweep gas contains nitrogen or the like, the energy required for its separation can be reduced, so that the oxygen generated in the electrolysis unit 2 can be used efficiently. The sweep gas can be manufactured by any method. The sweep gas may be combustion exhaust gas or biogas obtained by methane fermentation of organic matter, as long as it contains 50% or more by volume of carbon dioxide. Furthermore, if a small amount of reducing gas is supplied to the air electrode 22, it will burn immediately with oxygen, so there is no problem even if a small amount of reducing gas is supplied to the air electrode 22. Therefore, although it was stated that reducing gas is excluded from the components of the sweep gas, the sweep gas may contain a small amount (for example, less than 1% by volume) of reducing gas.

[0036] The sweep gas supply unit 3 includes a sweep gas supply path 3a through which the sweep gas flows, and a flow regulator 30 for adjusting the flow rate of the sweep gas. The sweep gas supply path 3a is connected to the sweep gas supply source on its upstream side and to the air electrode 22 of the electrolytic unit 2 on its downstream side. The flow regulator 30 may be provided on the sweep gas supply path 3a. Heaters such as heat exchangers or heaters for heating the sweep gas may be provided on the sweep gas supply path 3a.

[0037] The flow regulator 30 adjusts the flow rate of the sweep gas supplied to the air electrode 22 according to the flow rates of water vapor and carbon dioxide supplied to the fuel electrode 23, the electrolysis current of the electrolysis unit 2, etc. The flow regulator 30 is controlled by the control unit. The flow rate of the sweep gas is not particularly limited as long as it is sufficient to remove the oxygen generated at the air electrode 22, but it is preferable that the flow rate be such that the oxygen concentration of the oxygen-enriched gas, described later, is between 20 volume% and 50 volume%. If the oxygen concentration of the oxygen-enriched gas is 20 volume% or more, sufficient oxygen can be recovered, and if it is 50 volume% or less, corrosion of the piping on the outlet side of the air electrode 22 can be suppressed.

[0038] [Oxygen-enriched gas discharge section] The oxygen-enriched gas discharge unit 5 discharges oxygen-enriched gas, which is a mixture of oxygen generated at the air electrode 22 and sweep gas supplied to the air electrode 22. The oxygen-enriched gas discharge unit 5 is connected to the air electrode 22 and has an oxygen-enriched gas discharge passage 5a through which the oxygen-enriched gas flows. The oxygen-enriched gas discharge passage 5a may be a pipe connected to the air electrode 22, or it may be a flow path integrally formed in the electrolysis unit 2.

[0039] Since the electrolytic unit 2 normally operates at around 600°C to 1000°C, preferably around 650°C to 850°C, oxidation corrosion of the piping is likely to occur at the outlet side of the air electrode 22 in a high-temperature environment. For this reason, sweep gas is supplied to the air electrode 22 to reduce the oxygen concentration of the oxygen-enriched gas discharged from the air electrode 22, thereby suppressing oxidation corrosion. In addition, the supply of sweep gas also helps to homogenize the oxygen concentration at the air electrode 22, thereby mitigating concentration polarization.

[0040] Since the oxygen-enriched gas discharged from the electrolysis unit 2 is at a high temperature, a heat exchanger may be provided on the oxygen-enriched gas discharge passage 5a to recover the heat from the oxygen-enriched gas using a heat recovery medium (oil, water). The heat from the oxygen-enriched gas may be used to heat the sweep gas, or to heat the carbon dioxide, water, or steam supplied by the fuel gas supply unit 1.

[0041] The oxygen-enriched gas according to this embodiment is a mixture of oxygen generated at the air electrode 22 and a sweep gas mainly composed of carbon dioxide. Therefore, compared to using nitrogen or air as the sweep gas, oxygen can be separated from the oxygen-enriched gas more efficiently. For example, cryogenic separation separates each component from a mixture gas by utilizing the difference in boiling points. Since the boiling point of nitrogen is -196°C and the boiling point of carbon dioxide is -78.5°C, the energy required to cool the oxygen-enriched gas can be reduced. Even if the oxygen-enriched gas contains nitrogen or other elements derived from the sweep gas, according to this embodiment, the amount of nitrogen or other elements in the oxygen-enriched gas is small, so the energy required for separation can be reduced. Furthermore, since oxygen and carbon dioxide have different molecular sizes, carbon dioxide can also be separated by membrane separation. In addition, carbon dioxide can also be separated by amine absorption or physical adsorption. In this way, by supplying a sweep gas mainly composed of carbon dioxide to the air electrode 22 and separating components such as carbon dioxide from the oxygen-enriched gas discharged from the oxygen-enriched gas discharge unit 5, the oxygen generated at the air electrode 22 can be efficiently recovered, making effective use of the oxygen possible.

[0042] Furthermore, the oxygen-enriched gas discharged from the oxygen-enriched gas discharge section 5 may be used as a combustion-supporting gas for oxygen combustion without the separation of carbon dioxide. If the main component of the sweep gas is carbon dioxide, the amount of nitrogen in the oxygen-enriched gas can be reduced, thereby suppressing the generation of NOx due to combustion and leading to energy conservation. The oxygen-enriched gas may be used, for example, in a thermal power plant. Therefore, the electrolysis system 100 may be installed in a thermal power plant. The oxygen-enriched gas that has flowed through the oxygen-enriched gas discharge passage 5a may be collected in a tank or the like and transported to a thermal power plant, or it may be supplied directly to the oxygen combustion section of a thermal power plant.

[0043] [Electrolytic gas discharge section] The electrolytic gas discharge section 4 discharges the electrolytic gas containing hydrogen and carbon monoxide obtained from the fuel electrode 23 of the electrolytic section 2. The electrolytic gas may also contain water vapor or carbon dioxide. The electrolytic gas discharge section 4 is connected to the fuel electrode 23 and has an electrolytic gas flow passage 4a through which the electrolytic gas flows. Since the electrolytic gas is at a high temperature, it is preferable to provide a heat exchanger on the electrolytic gas flow passage 4a to recover the heat from the electrolytic gas. The electrolytic gas discharged from the electrolytic gas discharge section 4 may also be used for methane synthesis. In this case, it is preferable to provide a water separator on the electrolytic gas flow passage 4a to separate the water vapor contained in the electrolytic gas and a compressor to compress the electrolytic gas. Furthermore, it is preferable that the electrolytic gas flow passage 4a be connected downstream to a methanation device that produces a product gas containing water and methane from hydrogen and carbon monoxide or carbon dioxide through a methanation reaction.

[0044] [Second Embodiment] Next, the electrolysis system 100 according to the second embodiment will be described with reference to Figure 2. The electrolysis system 100 according to the second embodiment includes a separation unit 6 that separates oxygen from the oxygen-enriched gas, and a separation gas supply path 6a through which the separated gas, which is mainly composed of carbon dioxide and separated from the oxygen-enriched gas in the separation unit 6, flows. The other configurations are the same as in the first embodiment, so the same configurations as in the first embodiment will not be described.

[0045] The separation unit 6 absorbs carbon dioxide by means of, for example, amine absorption, physical adsorption, or membrane separation, and separates carbon dioxide from the oxygen-enriched gas. The amine absorption method has a high carbon dioxide absorption capacity and can efficiently separate carbon dioxide even from high-pressure or high-temperature mixed gases, so it is preferable for the separation unit 6 to separate carbon dioxide by the amine absorption method. If it is not necessary to obtain high-purity oxygen in the separation unit 6, the separation unit 6 may separate only carbon dioxide. However, if high-purity oxygen is to be obtained, the separation unit 6 may also separate components other than carbon dioxide (for example, nitrogen) contained in the oxygen-enriched gas, and may be a cryogenic separation apparatus. If the main component of the sweep gas is carbon dioxide, even if nitrogen or other elements are contained in the sweep gas, the energy required for their separation can be reduced, allowing for more efficient separation of oxygen from the oxygen-enriched gas. Furthermore, the higher the carbon dioxide concentration in the sweep gas, the higher the purity of oxygen that can be obtained by separating only carbon dioxide, thus simplifying the equipment and reducing separation energy.

[0046] The separated gas (e.g., carbon dioxide) separated in the separation unit 6 may be supplied to the air electrode 22 via the separated gas supply passage 6a. That is, the sweep gas may contain the separated gas separated in the separation unit 6. The separated gas supply passage 6a is connected to the separation unit 6 on the upstream side, for example, and to the sweep gas supply passage 3a on the downstream side. A flow regulator 60 for adjusting the flow rate of the separated gas may be provided on the separated gas supply passage 6a.

[0047] The separated gas in the separation unit 6 may be a mixed gas containing carbon dioxide and nitrogen, or it may be a gas separated by its respective component. When separating multiple components in the separation unit 6, multiple flow paths may be provided for each gas separated by component. If the separated gas is a mixed gas containing carbon dioxide and nitrogen, the flow rates of the gas flowing through the sweep gas supply path 3a and the separated gas supply path 6a may be adjusted by the flow regulators 30 and 60 so that carbon dioxide becomes the main component of the sweep gas. Measuring instruments for measuring the temperature, components, or concentration of the sweep gas or separated gas may be installed on the sweep gas supply path 3a or the separated gas supply path 6a, and the flow regulators 30 and 60 may be controlled by the control unit based on the temperature, components, or concentration of the sweep gas or separated gas measured by the measuring instruments.

[0048] In the electrolysis system 100 according to this embodiment, the separated gas separated in the separation unit 6 is reused, so the separated gas and the heat of the separated gas can be effectively utilized. Heat exchangers may be provided on the oxygen-enriched gas discharge path 5a and the separated gas supply path 6a to exchange heat between the oxygen-enriched gas and the separated gas flowing through them. As a result, the heat of the oxygen-enriched gas can be used to preheat the separated gas, so the energy required to heat the sweep gas can be reduced, and the overall heat management of the electrolysis system 100 can be efficiently performed.

[0049] [Other Embodiments] (a) In the first embodiment, the oxygen-enriched gas discharged from the oxygen-enriched gas discharge unit 5 may be used as a combustion-supporting gas for oxygen combustion, but the exhaust gas containing carbon dioxide after oxygen combustion may also be reused as sweep gas. Since the exhaust gas components after oxygen combustion are mainly water and carbon dioxide, a high concentration of carbon dioxide gas can be obtained by removing the water. By using such carbon dioxide gas as sweep gas, the carbon dioxide concentration in the sweep gas can be increased, making it possible to recover a high concentration of oxygen from the oxygen-enriched gas by separating only the carbon dioxide.

[0050] (b) In the first embodiment, the sweep gas supply passage 3a is connected to the sweep gas supply source on its upstream side, but as shown in Figure 3, it may be branched from the carbon dioxide supply passage 12a on the upstream side of the confluence passage 13a. A flow regulator that serves as both a flow regulator 120 and a flow regulator 30 may be placed at the branching point of the carbon dioxide supply passage 12a. In this embodiment, the carbon dioxide supplied to the fuel electrode 23 is also supplied to the air electrode 22 as sweep gas. Since sweep gas with a high carbon dioxide concentration is supplied to the air electrode 22, the main components of the oxygen-enriched gas are oxygen and carbon dioxide, and it is possible to obtain a high concentration of oxygen by separating carbon dioxide from the oxygen-enriched gas. Furthermore, when the oxygen-enriched gas is used as a combustion-supporting gas for oxygen combustion, the carbon dioxide concentration in the exhaust gas can also be increased, and it is possible to reuse the carbon dioxide in the exhaust gas.

[0051] (c) In the above embodiment, the electrolytic unit 2 is said to have a solid electrolyte 21, but it is not limited to a solid electrolyte 21 as long as it can transport oxygen ions, and instead of the solid electrolyte 21, it may have, for example, an anion exchange membrane (AEM).

[0052] (d) In the above embodiment, the electrolysis unit 2 performs co-electrolysis of water and carbon dioxide, but it may also perform electrolysis of either water or carbon dioxide. In this case, the fuel gas supply unit 1 may have either a water vapor supply unit 11 or a carbon dioxide supply unit 12. Furthermore, the electrolysis gas discharge unit 4 discharges an electrolysis gas containing either hydrogen or carbon monoxide.

[0053] The configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. Furthermore, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto and can be modified as appropriate without departing from the object of the present invention. [Industrial applicability]

[0054] The present invention can be used in an electrolytic system comprising an electrolytic section having at least a fuel electrode, an air electrode, and an electrolyte disposed between the fuel electrode and the air electrode. [Explanation of Symbols]

[0055] 1: Fuel gas supply unit 2: Electrolytic part 3: Sweep gas supply unit 4: Electrolytic gas discharge section 5: Oxygen-enriched gas discharge section 6: Separation part 21: Solid electrolyte (electrolyte) 22: Air pole 23:Fuel electrode 100: Electrolytic System

Claims

1. An electrolytic unit having at least a fuel electrode, an air electrode, and an electrolyte disposed between the fuel electrode and the air electrode, A fuel gas supply unit that supplies at least one of water vapor and carbon dioxide to the fuel electrode, A sweep gas supply unit that supplies a sweep gas mainly composed of carbon dioxide to the air electrode, An electrolytic gas discharge unit that discharges an electrolytic gas containing at least one of hydrogen and carbon monoxide produced at the fuel electrode, An electrolysis system comprising: an oxygen-enriched gas discharge unit that discharges oxygen-enriched gas containing oxygen generated at the air electrode.

2. The electrolysis system according to claim 1, wherein the carbon dioxide concentration of the sweep gas is 80% by volume or more.

3. The electrolysis system according to claim 1 or 2, wherein the oxygen concentration of the oxygen-enriched gas is 20% by volume or more and 50% by volume or less.

4. The electrolysis system according to claim 1, further comprising a separation unit for separating oxygen from the oxygen-enriched gas discharged from the oxygen-enriched gas discharge unit.

5. The electrolytic system according to claim 4, wherein the sweep gas includes a separated gas from which oxygen has been separated in the separation unit.

6. The electrolytic system according to claim 1, wherein the oxygen-enriched gas is used for oxygen combustion.

7. The electrolytic system according to claim 1, wherein the electrolyte is a solid oxide.

8. The fuel gas supply unit supplies the water vapor and carbon dioxide to the fuel electrode. The electrolytic unit performs co-electrolysis of the water vapor and the carbon dioxide. The electrolytic system according to claim 1, wherein the electrolytic gas discharge unit discharges the electrolytic gas containing the hydrogen and carbon monoxide generated at the fuel electrode.

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