Water electrolysis apparatus and method

Abstract

To effectively utilize oxygen generated at the same time when hydrogen is generated by water vapor electrolysis in a water electrolytic cell.SOLUTION: A water electrolysis apparatus of the present invention comprises: a water electrolytic cell for generating a hydrogen at a fuel electrode, and at the same time, oxygen at an oxidizer electrode by water vapor electrolysis; an oxidizer electrode off-gas passage into which an oxidizer electrode off-gas including the oxygen flows from the oxidizer electrode; an air passage communicating to the oxidizer electrode off-gas passage; and an air supply device for supplying air to the air passage. The water electrolysis apparatus also includes an oxygen-enriched air generation system for generating an oxygen-enriched air by mixing the air from the air supply device and the oxidizer electrode off-gas, which flows into the air passage from the oxidizer electrode off-gas passage, in the air passage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a water electrolysis device and method for producing hydrogen at an anode of a water electrolysis cell and oxygen at an oxidizer electrode of the water electrolysis cell by steam electrolysis. [Background technology]

[0002] Conventionally, a power plant equipped with a solid electrolyte cell capable of reversible operation as a water electrolysis cell and a fuel cell is known (for example, see Patent Document 1). In this power plant, hydrogen and oxygen are generated by steam electrolysis in the solid electrolyte cell using surplus power, and the generated hydrogen and oxygen are stored in the corresponding hydrogen tank or oxygen tank. When hydrogen and oxygen are generated by steam electrolysis, water vapor is produced using main steam from the power plant. Furthermore, the water vapor is heated in a combustor to which oxygen stored in an oxygen tank is supplied and is supplied to the fuel electrode of the solid electrolyte cell, and oxygen from the oxygen tank, which is heated in a combustor that combusts hydrogen stored in a hydrogen tank, is supplied to the oxidizer electrode of the solid electrolyte cell. On the other hand, when the demand for electricity increases, hydrogen from the hydrogen tank and oxygen from the oxygen tank are supplied to the solid electrolyte cell to generate electricity.

[0003] Also, a hydrogen production system that produces hydrogen from water vapor as fuel using a solid oxide electrolysis cell (SOEC: Solid Oxide Electrolysis Cell) is known (see, for example, Patent Document 2). This hydrogen production system includes a fuel-side heat exchanger that heats water vapor using a fuel electrode off-gas discharged from the fuel electrode of the water electrolysis cell as a heat source, and an oxygen-side heat exchanger that heats water vapor using an oxidizer electrode off-gas discharged from the oxidizer electrode of the water electrolysis cell as a heat source. The fuel electrode off-gas that has passed through the fuel-side heat exchanger is separated into water and hydrogen in a gas-liquid separator, and the hydrogen is boosted by a booster and then stored in a hydrogen storage tank. The oxidizer electrode off-gas that has passed through the oxygen-side heat exchanger is stored in a tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-160404 A [Patent Document 2] JP 2022-144623 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the power plant described in Patent Document 1, oxygen produced together with hydrogen in a water electrolysis cell by steam electrolysis is used to heat the steam and as an oxidant for operating a solid electrolyte cell as a fuel cell. However, in these applications, oxygen can be substituted with air, and it cannot be said that oxygen, which is a by-product of hydrogen production, is necessarily used effectively in the power plant. Furthermore, Patent Document 2 does not disclose any form of utilization of the oxidizer electrode off-gas, i.e., oxygen, stored in a tank.

[0006] Therefore, a main object of the present disclosure is to effectively utilize oxygen that is produced together with hydrogen in a water electrolysis cell by steam electrolysis. [Means for solving the problem]

[0007] The water electrolysis device disclosed herein is a water electrolysis device including a water electrolysis cell that produces hydrogen at a fuel electrode by steam electrolysis and produces oxygen at an oxidizer electrode, the water electrolysis device having an oxidizer electrode off-gas passage into which oxidizer electrode off-gas containing oxygen flows from the oxidizer electrode, an air passage communicating with the oxidizer electrode off-gas passage, and an oxygen-enriched air generation system that mixes air from the air supply device and the oxidizer electrode off-gas flowing from the oxidizer electrode off-gas passage into the air passage in the air passage to generate oxygen-enriched air.

[0008] The water electrolysis device disclosed herein includes an oxygen-enriched air generation system having an air passage communicating with an oxidizer electrode off-gas passage into which oxidizer electrode off-gas containing oxygen flows from an oxidizer electrode, and an air supply device that supplies air to the air passage. The oxygen-enriched air generation system mixes air from the air supply device and oxidizer electrode off-gas flowing from the oxidizer electrode off-gas passage into the air passage in the air passage to generate oxygen-enriched air having an oxygen concentration higher than the usual 21%. As a result, the water electrolysis device disclosed herein can obtain oxygen-enriched air, which can be widely used as, for example, high-concentration oxygen for medical use or an oxidizer for combustion, as a by-product when hydrogen is generated in a water electrolysis cell by steam electrolysis. Furthermore, the water electrolysis device disclosed herein can generate oxygen-enriched air more efficiently and at lower cost than a method using a gas separation membrane (oxygen-enriched membrane) or a PSA method (adsorption method), and the oxygen concentration in the oxygen-enriched air can be easily adjusted to a value corresponding to various applications by controlling the flow rate of air supplied to the air passage. As a result, it is possible to effectively utilize the oxygen generated together with hydrogen in the water electrolysis cell by steam electrolysis. In addition, by utilizing and selling oxygen-enriched air, which is a by-product of hydrogen production, it is possible to improve the efficiency of hydrogen production and reduce the production cost of hydrogen.

[0009] The water electrolysis method disclosed herein produces hydrogen at a fuel electrode of a water electrolysis cell by steam electrolysis and produces oxygen at an oxidant electrode of the water electrolysis cell, the method comprising: supplying air from an air supply device to an air passage communicating with an oxidant electrode off-gas passage into which oxidant electrode off-gas containing oxygen flows from the oxidant electrode; and mixing, in the air passage, the air from the air supply device and the oxidant electrode off-gas flowing from the oxidant electrode off-gas passage into the air passage to produce oxygen-enriched air.

[0010] This method makes it possible to effectively utilize the oxygen that is produced together with hydrogen in the water electrolysis cell by steam electrolysis, and by utilizing and selling oxygen-enriched air, which is a by-product of hydrogen production, it is possible to improve the efficiency of hydrogen production and reduce the production cost of hydrogen. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram showing a water electrolysis device according to the present disclosure. [Diagram 2] FIG. 2 is a schematic configuration diagram showing another water electrolysis device according to the present disclosure. [Diagram 3] FIG. 2 is a schematic configuration diagram showing still another water electrolysis device according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Next, an embodiment of the present disclosure will be described with reference to the drawings.

[0013] Fig. 1 is a schematic diagram showing a water electrolysis apparatus 1 of the present disclosure. The water electrolysis apparatus 1 shown in the figure includes a water electrolysis module 20 including a water electrolysis cell stack 2 that produces hydrogen by steam electrolysis, a water vapor supply system 3 that supplies water vapor as fuel to the water electrolysis module 20, a blower 4 that supplies air as a sweep gas to the water electrolysis module 20, a hydrogen recovery system 5 that recovers hydrogen produced in the water electrolysis cell stack 2, a power source 6, and a controller 10 that controls the entire system.

[0014] The water electrolysis cell stack 2 includes a plurality of solid oxide electrolysis cells (SOEC, hereinafter referred to as "single cells") stacked in a predetermined direction. Each single cell includes an electrolyte 2a, a fuel electrode 2b arranged on one side of the electrolyte 2a, and an oxidizer electrode 2c arranged on the other side of the electrolyte 2a. The electrolyte 2a is a solid electrolyte such as stabilized zirconia (e.g., YSZ). The fuel electrode 2b is formed of a composite material of a catalytic metal such as Ni and stabilized zirconia. The oxidizer electrode 2c is formed of a ceramic such as LSCF.

[0015] Each single cell electrolyzes water vapor in a high-temperature environment of, for example, 650-800°C in response to application of power from the power source 6, generating hydrogen at the fuel electrode 2b and oxygen at the oxidizer electrode 2c. The single cell may be a reversible water electrolysis cell that generates hydrogen and oxygen by steam electrolysis and generates electricity by an electrochemical reaction between the hydrogen and oxygen. The power source 6 may be a system power source, a renewable energy power generation facility, a storage battery, or a combination of these.

[0016] The water electrolysis module 20 includes various pipes and a plurality of heat exchangers in addition to the water electrolysis cell stack 2, and these components of the water electrolysis module 20 are housed in a module case 21 formed of a heat insulating material. As shown in FIG. 1 , a fuel supply pipe 22 forming a fuel supply passage is connected to an anode inlet of the water electrolysis cell stack 2, and the fuel supply pipe 22 is connected to a water vapor supply system 3 outside the module case 21 via a heat exchanger 23. Furthermore, a fuel electrode off-gas pipe 24 forming a fuel electrode off-gas passage is connected to an anode outlet of the water electrolysis cell stack 2, and anode off-gas containing hydrogen from the anode 2b of each unit cell flows into the anode off-gas pipe 24. The anode off-gas pipe 24 includes a heat transfer pipe disposed in the heat exchanger 23 in the middle, and is connected to a hydrogen recovery system 5 outside the module case 21. That is, the anode off-gas flowing through the anode off-gas pipe 24 is used as a heat source for the heat exchanger 23.

[0017] An air supply pipe 25 forming an air supply passage is connected to an oxidizer electrode inlet of the water electrolysis cell stack 2, and the air supply pipe 25 is connected to a blower 4 (second air supply device) outside the module case 21 via a heat exchanger 26. An oxidizer electrode off-gas pipe 27 forming an oxidizer electrode off-gas passage is connected to an oxidizer electrode outlet of the water electrolysis cell stack 2, and oxidizer electrode off-gas containing oxygen from the oxidizer electrode 2c of each unit cell flows into the oxidizer electrode off-gas pipe 27. The oxidizer electrode off-gas pipe 27 includes a heat transfer pipe arranged in the heat exchanger 26 in the middle, and the oxidizer electrode off-gas flowing through the oxidizer electrode off-gas pipe 27 is used as a heat source for the heat exchanger 26.

[0018] The water vapor supply system 3 includes a water tank for storing water (raw water), a water pump for sucking in and discharging water from the water tank, an evaporator for vaporizing water from the water pump, a heater, and the like (all not shown). The water vapor from the water vapor supply system 3 is heated to a required temperature by heat exchange with the fuel electrode off-gas in the heat exchanger 23 in the module case 21, and then supplied to the fuel electrode 2b of each unit cell through the fuel supply pipe 22 and the fuel electrode inlet of the water electrolysis cell stack 2. The blower 4 sucks in and discharges air through an air filter (not shown). The air from the blower 4 is heated to a required temperature by heat exchange with the oxidizer electrode off-gas in the heat exchanger 26 in the module case 21, and then supplied to the oxidizer electrode 2c of each unit cell through the air supply pipe 25 and the oxidizer electrode inlet of the water electrolysis cell stack 2. This allows oxygen generated at the oxidizer electrode 2c of each unit cell to flow out to the oxidizer electrode off-gas pipe 27 together with the air from the blower 4, i.e., the sweep gas.

[0019] The hydrogen recovery system 5 recovers hydrogen from the anode off-gas flowing into the anode off-gas pipe 24, and includes a gas-liquid separator 50 and a hydrogen tank 51. The gas-liquid separator 50 exchanges heat between the anode off-gas from the anode off-gas pipe 24 and cooling water to condense the water vapor contained in the anode off-gas. The anode off-gas separated into gas and liquid in the gas-liquid separator 50, i.e., hydrogen, is pumped into the hydrogen tank 51 by a pump (not shown). The condensed water condensed in the gas-liquid separator 50 is collected in the water tank of the water vapor supply system 3 and used as raw water for water vapor. Furthermore, a hydrogen supply pump 55 is connected to the pipe connecting the gas-liquid separator 50 and the hydrogen tank 51 or to the hydrogen tank 51 via a pipe. The hydrogen supply pump 55 mixes hydrogen from the gas-liquid separator 50 or the hydrogen tank 51 with water vapor supplied to the fuel supply pipe 22 from the water vapor supply system 3 as an antioxidant. This makes it possible to maintain the fuel electrode 2b of each unit cell in a reducing atmosphere and effectively suppress oxidation of the catalytic metal.

[0020] The control device 10 includes a computer having a CPU, ROM, RAM, input / output devices, etc. The control device 10 acquires signals from a temperature sensor (not shown) installed near the water electrolysis cell stack 2, a flow meter (not shown) in the water vapor supply system 3, a flow meter 4f that detects the flow rate of air supplied from the blower 4 to the air supply pipe 25, etc. Then, the control device 10 controls controlled objects such as the water vapor supply system 3, the blower 4, the hydrogen supply pump 55, and the power source 6 based on the acquired signals, etc.

[0021] Here, by effectively utilizing oxygen generated together with hydrogen in the water electrolysis cell stack 2 by steam electrolysis, the added value of the water electrolysis apparatus 1 can be further increased. For this reason, the water electrolysis apparatus 1 of this embodiment is provided with an oxygen-enriched air generation system 7 that generates oxygen-enriched air having an oxygen concentration higher than the normal 21% from oxygen generated at the oxidizer electrode 2c of each unit cell. The oxygen-enriched air can be widely used, for example, as high-concentration oxygen for medical use or an oxidizer for combustion. As shown in FIG. 1, the oxygen-enriched air generation system 7 includes an air pipe (air passage) 70 that communicates with the oxidizer electrode off-gas pipe 27 of the water electrolysis module 20, a blower 75 as an air supply device that supplies air to the air pipe 70, and an air tank 77. As shown in the figure, the air pipe 70, the blower 75, and the air tank 77 are all installed outside the water electrolysis module 20.

[0022] One end of the air pipe 70 is connected to a discharge port of a blower 75, and the other end of the air pipe 70 is connected to an air inlet of an air tank 77. A tip (an end downstream of the heat exchanger 26) of an oxidizer electrode off-gas pipe 27 of the water electrolysis module 20 is connected to the air pipe 70 via a pipe joint between the blower 75 and the air tank 77. This allows the inside of the air pipe 70 and the inside of the oxidizer electrode off-gas pipe 27 to communicate with each other. The blower 75 is controlled by the control device 10, and sucks in air through an air filter (not shown) and supplies (discharges) it into the air pipe 70. A flow meter 7f for detecting the flow rate of air supplied from the blower 75 to the air pipe 70 is provided in the air pipe 70.

[0023] While hydrogen is produced in the water electrolysis cell stack 2 by steam electrolysis, the control device 10 sets a target air flow rate Frtag of air supplied from the blower 75 to the air pipe 70 in accordance with the following equation (1) at predetermined time intervals (microtimes), and controls (feedback controls) the blower 75 so that the air flow rate detected by the flow meter 7f becomes the target air flow rate Frtag. In this way, the air from the blower 75 and the oxidizer electrode off-gas containing oxygen flowing from the oxidizer electrode off-gas pipe 27 into the air pipe 70 are mixed in the air pipe 70 to produce oxygen-enriched air, and the produced oxygen-enriched air can be stored in the air tank 77.

[0024] Frtag=〔(C-100)×A+(C-21)×B〕 / (21-C) …(1)

[0025] In formula (1), “A” is the amount of oxygen produced in the water electrolysis module 20 [L / min], and the reaction formula (2O 2- →O2+4e - ) etc., A=1 / 4×(I×n) / F×22.4×60 …(2) In formula (2), "I" is the current [A] applied from the power source 6 to each unit cell of the water electrolysis cell stack 2, "n" is the number of cells connected in series in the water electrolysis cell stack 2, and "F" is the Faraday constant (=96485.33 [As / mol]). In formula (1), "B" is the flow rate [L / min] of air as a sweep gas detected by the flowmeter 4f, and "C" is the target concentration [Vol%] of oxygen-enriched air. The target concentration of oxygen-enriched air is predetermined to, for example, about 40% for high-concentration oxygen for medical use and about 25-30% for an oxidizer for combustion.

[0026] As described above, the water electrolysis device 1 includes an oxygen-enriched air generation system 7 having an air pipe 70 communicating with the oxidizer electrode off-gas pipe 27 into which oxidizer electrode off-gas containing oxygen flows from the oxidizer electrode 2c of each unit cell in the water electrolysis cell stack 2, and a blower 75 serving as an air supply device that supplies air to the air pipe 70. The oxygen-enriched air generation system 7 mixes, within the air pipe 70, air from the blower 75 and the oxidizer electrode off-gas flowing into the air pipe 70 from the oxidizer electrode off-gas pipe 27, to generate oxygen-enriched air having an oxygen concentration higher than the normal 21%.

[0027] As a result, when hydrogen is generated in the water electrolysis cell stack 2 by steam electrolysis, the water electrolysis device 1 can obtain oxygen-enriched air as a by-product, which can be widely used, for example, as high-concentration oxygen for medical use or as an oxidizing agent for combustion. Furthermore, the water electrolysis device 1 can generate oxygen-enriched air more efficiently and at lower cost than a method using a gas separation membrane (oxygen-enriched membrane) or the PSA method (adsorption method), and the oxygen concentration in the oxygen-enriched air can be easily adjusted to a value suitable for various applications by controlling the flow rate of air supplied from the blower 75 to the air pipe 70. As a result, oxygen generated together with hydrogen in the water electrolysis cell stack 2 by steam electrolysis can be effectively utilized. In addition, the utilization and sale of the oxygen-enriched air, which is a by-product of hydrogen, can improve the hydrogen production efficiency and reduce the production cost of hydrogen.

[0028] The water electrolysis device 1 also includes a blower 4 (second air supply device) that supplies air to the oxidant electrode 2c of each unit cell so as to cause oxygen generated at the oxidant electrode 2c of each unit cell in the water electrolysis cell stack 2 to flow into the oxidant electrode off-gas pipe 27, and a flow meter (second flow meter) 4f that detects the flow rate of air (sweep gas) supplied from the blower 4 to the oxidant electrode 2c of each unit cell. Furthermore, the control device 10 sets a target air flow rate Frtag based on the current I applied to the water electrolysis cell stack 2 (each unit cell), the target oxygen concentration C of the oxygen-enriched air, and the detection value of the flow meter 4f, and controls the blower 75 so that the air flow rate detected by the flow meter 7f becomes the target air flow rate Frtag. This makes it possible to more reliably ensure that the oxygen generated at the oxidizer electrode 2c of each single cell flows into the oxidizer electrode off-gas pipe 27, and also makes it possible to more appropriately adjust the flow rate of air supplied from the blower 75 to the air pipe 70 so that the oxygen concentration of the oxygen-enriched air becomes the target oxygen concentration C, taking into account the flow rate of air as a sweep gas supplied from the blower 4 to the oxidizer electrode 2c of each single cell.

[0029] Furthermore, in the water electrolysis device 1, a solid oxide electrolysis cell with extremely high Faraday efficiency is used as each unit cell of the water electrolysis cell stack 2. This improves the efficiency of hydrogen production by steam electrolysis and enables more precise adjustment of the oxygen concentration of oxygen-enriched air. In addition, in the solid oxide electrolysis cell, no water is present at the oxidizer electrode 2c, making it unnecessary to perform gas-liquid separation processing for the oxidizer electrode off-gas, and thus the production efficiency of hydrogen and oxygen-enriched air can be further improved.

[0030] 2 is a schematic diagram showing another water electrolysis apparatus 1B according to the present disclosure. Among the components of the water electrolysis apparatus 1B, the same components as those of the above-described water electrolysis apparatus 1 are designated by the same reference numerals, and redundant description will be omitted.

[0031] 2 corresponds to the water electrolysis apparatus 1 shown in FIG 1 without the blower 4, the flow meter 4f, the air supply pipe 25, and the heat exchanger 26. In the water electrolysis apparatus 1B, an end of the oxidizer electrode off-gas pipe 27B (the end opposite the water electrolysis cell stack 2) is connected to the air pipe 70 via a pipe joint between the blower 75 and the air tank 77, without passing through a heat exchanger or the like. While hydrogen is produced in the water electrolysis cell stack 2 by steam electrolysis, the control device 10B of the water electrolysis apparatus 1B sets a target air flow rate Frtag of air supplied from the blower 75 to the air pipe 70 according to the following equation (3) at predetermined time intervals (microtimes), and controls (feedback controls) the blower 75 so that the air flow rate detected by the flow meter 7f becomes the target air flow rate Frtag. In formula (3), "A" is the amount of oxygen produced in the water electrolysis module 20 [L / min] and is expressed as in formula (2) above, and "C" is the target concentration of oxygen-enriched air [Vol%].

[0032] Frtag=(C-100)×A / (21-C) …(3)

[0033] That is, the control device 10B of the water electrolysis apparatus 1B sets the target air flow rate Frtag based on the current I applied to the water electrolysis cell stack 2 (each unit cell) and the target oxygen concentration C of the oxygen-enriched air, and controls the blower 75 so that the air flow rate detected by the flow meter 7f becomes the target air flow rate Frtag. This makes it possible, also in the water electrolysis apparatus 1B, to more appropriately adjust the flow rate of air supplied from the blower 75 to the air pipe 70 so that the oxygen concentration of the oxygen-enriched air becomes the target oxygen concentration C, and to mix the air from the blower 75 and the oxidant electrode off-gas in the air pipe 70 to generate the desired oxygen-enriched air.

[0034] 3 is a schematic diagram showing a configuration of still another water electrolysis apparatus 1C according to the present disclosure, in which the same components as those in the above-described water electrolysis apparatus 1 and the like are denoted by the same reference numerals and redundant description will be omitted.

[0035] 3 includes a combustor 28 that combusts a portion of the anode off-gas and a portion of the oxidant electrode off-gas inside the module case 21. The combustor 28 has an ignition device (not shown), and is connected to the anode off-gas pipe 24 of the water electrolysis module 20 via a bypass pipe (bypass passage) 24b branching off from the anode off-gas pipe 24, and is also connected to the oxidant electrode off-gas pipe 27C of the water electrolysis module 20. This allows a portion of the hydrogen generated by steam electrolysis to be efficiently combusted in the combustor 28 using the oxidant electrode off-gas as an oxidant.

[0036] Further, a combustion gas pipe 29 forming a combustion gas passage is connected to the combustor 28, and the combustion gas generated by the combustion of hydrogen flows into the combustion gas pipe 29. The combustion gas pipe 29 includes, in its middle, a heat transfer tube arranged in the heat exchanger 23C for raising the temperature of the water vapor, and a heat transfer tube arranged in the heat exchanger 26C for raising the temperature of the air serving as the sweep gas, and opens outside the module case 21. That is, the combustion gas flowing through the combustion gas pipe 29 is used as a heat source for the heat exchangers 23C and 26C.

[0037] Furthermore, in the water electrolysis apparatus 1C, a bypass pipe (bypass passage) 27b branches off from the oxidizer electrode off-gas pipe 27C between the water electrolysis cell stack 2 and the combustor 28, and the bypass pipe 27b is connected to the air pipe 70 via a pipe joint between the blower 75 and the air tank 77. That is, the inside of the air pipe 70 communicates with the inside of the oxidizer electrode off-gas pipe 27C between the water electrolysis cell stack 2 and the combustor 28 via the bypass pipe 27b. Furthermore, an orifice 27o is provided in the bypass pipe 27b so as to be located near the junction with the air pipe 70. As a result, a portion of the oxidizer electrode off-gas that flows from the oxidizer electrode 2c of each unit cell into the oxidizer electrode off-gas pipe 27C flows into the air pipe 70 via the bypass pipe 27b and the orifice 27o. The ratio (distribution ratio) of the oxidant electrode off-gas flowing into the air pipe 70 to the oxidant electrode off-gas flowing into the oxidant electrode off-gas pipe 27C is an approximately constant value that depends on the pressure losses in the oxidant electrode off-gas pipe 27C, the combustor 28, and the combustion gas pipe 29, and the pressure loss at the orifice 27o, if the orifice diameter of the orifice 27o is sufficiently small compared to the inner diameter of the air pipe 70.

[0038] While hydrogen is produced in the water electrolysis cell stack 2 by steam electrolysis, the control device 10C of the water electrolysis apparatus 1C sets a target air flow rate Frtag for the air supplied from the blower 75 to the air pipe 70 in accordance with the following equation (4) at predetermined time intervals (microtime intervals), and controls (feedback controls) the blower 75 so that the air flow rate detected by the flow meter 7f becomes the target air flow rate Frtag.

[0039] Frtag=〔(C-100)×A′+(C-21)×B〕 / (21-C) …(4)

[0040] In the formula (4), "A'" represents the amount of oxygen generated in the water electrolysis module 20 that is not used for combustion in the combustor 28 [L / min]. A′=1 / 4×(I×n) / F×22.4×60×Dr…(5) In addition, "Dr" in formula (5) is the ratio (distribution ratio) of the oxidant electrode off-gas flowing into the air pipe 70 to the oxidant electrode off-gas flowing into the oxidant electrode off-gas pipe 27C.

[0041] That is, the control device 10C of the water electrolysis device 1C sets a target air flow rate Frtag based on the current I applied to the water electrolysis cell stack 2 (each unit cell), the target oxygen concentration C of the oxygen-enriched air, and the ratio Dr of the oxidizer electrode off-gas flowing into the air pipe 70 to the oxidizer electrode off-gas flowing into the oxidizer electrode off-gas pipe 27C, and controls the blower 75 so that the air flow rate detected by the flowmeter 7f becomes the target air flow rate Frtag. As a result, in the water electrolysis device 1C, air from the blower 75 and oxidizer electrode off-gas containing oxygen flowing from the oxidizer electrode off-gas pipe 27C into the air pipe 70 are mixed in the air pipe 70 to generate oxygen-enriched air, and the generated oxygen-enriched air can be stored in the air tank 77.

[0042] In addition, in the water electrolysis apparatus 1C, a part of the hydrogen generated by steam electrolysis is efficiently combusted in the combustor 28 using the oxidizer electrode off-gas as an oxidizer, and the obtained heat can be used to efficiently heat the steam and the air as a sweep gas, thereby further improving the efficiency of steam electrolysis. In addition, in the water electrolysis apparatus 1C, the flow rate of the air supplied from the blower 75 to the air pipe 70 can be more appropriately adjusted so that the oxygen concentration of the oxygen-enriched air becomes the target oxygen concentration C while taking into account the amount of the oxidizer electrode off-gas used as an oxidizer, and the air from the blower 75 and the oxidizer electrode off-gas can be mixed in the air pipe 70 to generate oxygen-enriched air. Furthermore, by providing the orifice 27o in the bypass pipe 27b, the flow rate of the oxidizer electrode off-gas flowing from the bypass pipe 27b into the air pipe 70 can be increased, and the air from the blower 75 and the oxidizer electrode off-gas can be well mixed. However, the orifice 27o may be omitted from the bypass pipe 27b. Furthermore, the blower 4, the flow meter 4f, the air supply pipe 25, and the heat exchanger 26 may be omitted from the water electrolysis apparatus 1C.

[0043] The present disclosure is not limited to the above embodiment, and various modifications can be made within the scope of the present disclosure. Furthermore, the above embodiment is merely a specific form of the invention described in the Summary of the Invention, and does not limit the elements of the invention described in the Summary of the Invention. [Industrial Applicability]

[0044] The present disclosure is applicable to the water electrolysis device manufacturing industry, the hydrogen production industry, and the like. [Explanation of symbols]

[0045] 1, 1B, 1C water electrolysis device, 2 water electrolysis cell stack, 2a electrolyte, 2b fuel electrode, 2c oxidizer electrode, 3 water vapor supply system, 4 blower (second air supply device), 4f, 7f flow meter, 7 oxygen-enriched air generation system, 70 air pipe (air passage), 75 blower (air supply device), 10, 10B, 10C control device, 23, 23c, 26, 26C heat exchanger, 27, 27B, 27C oxidizer electrode off-gas pipe (oxidizer electrode off-gas passage), 28 combustor.

Claims

1. A water electrolysis device including a water electrolysis cell that generates hydrogen at a fuel electrode and oxygen at an oxidizer electrode by steam electrolysis, an oxidizer electrode off-gas passage into which an oxidizer electrode off-gas containing oxygen flows from the oxidizer electrode; an oxygen-enriched air generating system including an air passage communicating with the oxidizer electrode off-gas passage and an air supply device for supplying air to the air passage, the oxygen-enriched air generating system generating oxygen-enriched air by mixing, in the air passage, air from the air supply device and the oxidizer electrode off-gas flowing from the oxidizer electrode off-gas passage into the air passage; A water electrolysis device comprising:

2. The water electrolysis apparatus according to claim 1, a flow meter for detecting a flow rate of air supplied from the air supply device to the air passage; a control device that sets a target air flow rate based on a current applied to the water electrolysis cell and a target oxygen concentration of the oxygen-enriched air, and controls the air supply device so that the air flow rate detected by the flow meter becomes the target air flow rate; The water electrolysis device further comprises:

3. The water electrolysis apparatus according to claim 2, a second air supply device that supplies air to the oxidizer electrode so as to cause oxygen generated at the oxidizer electrode to flow into the oxidizer electrode off-gas passage; a second flow meter that detects a flow rate of air supplied from the second air supply device to the oxidizer electrode, The control device of the water electrolysis apparatus sets the target air flow rate based on the current applied to the water electrolysis cell, the target oxygen concentration of the oxygen-enriched air, and the detection value of the second flow meter.

4. The water electrolysis apparatus according to claim 2, an anode off-gas passage into which an anode off-gas flows from the anode of the water electrolysis cell; a combustor connected to the anode off-gas passage and the oxidizer electrode off-gas passage, for combusting a portion of the anode off-gas and a portion of the oxidizer electrode off-gas; a heat exchanger for exchanging heat between the combustion gas flowing out from the combustor and the water vapor supplied to the anode; Further comprising: the air passage communicates with the oxidizer electrode off-gas passage between the water electrolysis cell and the combustor; the control device of the water electrolysis device sets the target air flow rate based on a current applied to the water electrolysis cell, the target oxygen concentration of the oxygen-enriched air, and a ratio of the oxidizer electrode off-gas flowing into the air passage to the oxidizer electrode off-gas flowing into the oxidizer electrode off-gas passage.

5. 5. The water electrolysis apparatus according to claim 1, wherein the water electrolysis cell is a solid oxide electrolysis cell.

6. A water electrolysis method for producing hydrogen at a fuel electrode of a water electrolysis cell and producing oxygen at an oxidizer electrode of the water electrolysis cell by steam electrolysis, comprising: a water electrolysis method comprising: supplying air from an air supply device to an air passage communicating with an oxidizer electrode off-gas passage into which oxidizer electrode off-gas containing oxygen flows from the oxidizer electrode; and mixing, in the air passage, the air from the air supply device and the oxidizer electrode off-gas flowing from the oxidizer electrode off-gas passage into the air passage to generate oxygen-enriched air.

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