Electrolytic system

Abstract

It suppresses the generation of nitrogen oxides and recovers high-purity oxygen. [Solution] The electrolytic system comprises an electrolytic cell that generates hydrogen and oxygen by electrolyzing water vapor; a water vapor supply line that supplies water vapor to the electrolytic cell; an oxidant supply line that supplies an oxidant gas to the electrolytic cell; a combustion section that burns hydrogen using oxygen electrode off-gas containing oxygen discharged from the electrolytic cell as a combustion aid and discharges combustion exhaust gas containing water vapor and unburned oxygen; an oxygen recovery line that recovers oxygen from the combustion exhaust gas; and a recirculation line that branches off from the oxygen recovery line and is connected to the oxidant supply line.

Description

Technical Field

[0004] ,

[0006] , , , , , ,

[0005] , , ,

[0003] , , ,

[0001] This specification discloses an electrolysis system.

Background Art

[0002] Conventionally, a system has been proposed in which a supply gas on the anode (oxygen electrode) side containing carbon dioxide is supplied to the anode side of a solid oxide type electrolysis cell during operation to generate an oxygen-rich gas with a low nitrogen content, and the generated oxygen-rich gas is supplied to an oxygen consumption process (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an electrolysis system including a solid oxide type electrolysis cell and a combustion unit that burns combustion hydrogen using oxygen electrode off-gas discharged from the oxygen electrode of the electrolysis cell as a combustion support gas, when air is supplied as a sweep gas to the oxygen electrode, there is a risk that the performance of the cell may be degraded by nitrogen contained in the air or nitrogen oxides may be generated in the combustion unit. In the system described in Patent Document 1 mentioned above, although the generation of nitrogen oxides can be reduced because a supply gas containing carbon dioxide with a low nitrogen content is supplied to the oxygen electrode side of a solid oxide type electrolysis cell during operation, it is difficult to recover highly pure oxygen because the supply gas is mixed with the oxygen generated on the oxygen electrode side.

[0005] The main object of the present disclosure is to provide an electrolysis system capable of suppressing the generation of nitrogen oxides and recovering highly pure oxygen.

Means for Solving the Problems

[0006] This disclosure employs the following means to achieve the primary objectives described above.

[0007] The electrolytic system of this disclosure comprises: an electrolytic cell that generates hydrogen and oxygen by electrolyzing water vapor; a water vapor supply line that supplies the water vapor to the electrolytic cell; an oxidant supply line that supplies an oxidant gas to the electrolytic cell; a combustion unit that burns hydrogen using oxygen electrode off-gas containing oxygen discharged from the electrolytic cell as a combustion aid and discharges combustion exhaust gas containing water vapor and unburned oxygen; an oxygen recovery line that recovers oxygen from the combustion exhaust gas; and a reflux line that branches off from the oxygen recovery line and is connected to the oxidant supply line.

[0008] In the electrolytic system of this disclosure, oxygen-rich gas containing oxygen generated by the electrolytic operation of the electrolytic cell is circulated internally. Compared to systems that supply air to the electrolytic cell during electrolytic operation, the proportion of nitrogen in the circulating gas can be reduced, thereby suppressing the generation of nitrogen oxides in the combustion section. Furthermore, since the generated oxygen produced at the oxygen electrode circulates between the oxygen electrode and the combustion section, high-purity oxygen can be recovered from the combustion exhaust gas generated in the combustion section. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the electrolysis system 10 of this embodiment. [Figure 2] This is a flowchart showing an example of a control process. [Modes for carrying out the invention]

[0010] Next, the forms for implementing this disclosure will be described with reference to the drawings.

[0011] Figure 1 is a schematic diagram of the electrolysis system 10 of this embodiment. The electrolysis system 10 of this embodiment includes an electrolysis module 20 including an electrolysis cell stack 21 that generates hydrogen by steam electrolysis, a power supply device 29 that supplies the power necessary for steam electrolysis to the electrolysis cell stack 21, a steam supply system 30 that supplies steam to the electrolysis module 20, a hydrogen supply system 40 that supplies hydrogen to the electrolysis module 20, an air supply system 50 that supplies air to the electrolysis module 20, a hydrogen recovery system 60 that recovers the hydrogen generated in the electrolysis cell stack 21, an oxygen recovery system 70 that recovers the oxygen generated in the electrolysis cell stack 21, and a control device 80 that controls the entire system.

[0012] The electrolytic module 20 includes an electrolytic cell stack 21, a combustor 22, a fuel preheater 24, and heat exchangers 25, 26, and 27, all of which are housed in an insulated module case 28.

[0013] The electrolytic cell stack 21 comprises a plurality of solid oxide single cells, each containing a solid electrolyte, a hydrogen electrode positioned on one side of the solid electrolyte, and an oxygen electrode positioned on the other side of the solid electrolyte. The electrolytic cell stack 21 is supplied with water vapor from the hydrogen electrode inlet and power from the power supply device 29, causing the water vapor to be electrolyzed to produce hydrogen at the hydrogen electrode and oxygen at the oxygen electrode. The hydrogen produced at the hydrogen electrode (generated hydrogen) is discharged from the hydrogen electrode outlet as a hydrogen electrode off-gas along with unreacted water vapor, and the oxygen produced at the oxygen electrode is discharged from the oxygen electrode outlet as an oxygen electrode off-gas along with a sweep gas supplied from the oxygen electrode inlet. The power supply device 29 can be a grid power supply, a renewable energy device (e.g., a solar power generation device), or a storage battery.

[0014] Since the electrolytic cell stack 21 operates in a high-temperature environment, for example, 650-800°C, the solid electrolyte, hydrogen electrode, and oxygen electrode are made of ceramic material. Furthermore, because the catalyst decomposes water vapor into oxygen ions and hydrogen, a cermet made of a catalytic metal such as nickel and ceramic is used for the hydrogen electrode. In order to maintain good catalytic activity of the hydrogen electrode, it is necessary to keep the hydrogen electrode in a reducing atmosphere and prevent oxidation of the metal. For this reason, in this embodiment, hydrogen is mixed into the water vapor supplied to the hydrogen electrode to prevent oxidation.

[0015] One end of the hydrogen electrode inlet pipe 21a is connected to the hydrogen electrode inlet of the electrolytic cell stack 21, and the other end of the hydrogen electrode inlet pipe 21a is connected to the steam supply system 30 and the hydrogen supply system 40. One end of the oxygen electrode inlet pipe 21b is connected to the oxygen electrode inlet of the electrolytic cell stack 21, and the other end of the oxygen electrode inlet pipe 21b is connected to the air supply system 50. One end of the hydrogen electrode outlet pipe 21c is connected to the hydrogen electrode outlet of the electrolytic cell stack 21, and the other end of the hydrogen electrode outlet pipe 21c is connected to the hydrogen recovery system 60. One end of the oxygen electrode outlet pipe 21d is connected to the oxygen electrode outlet of the electrolytic cell stack 21, and the other end of the oxygen electrode outlet pipe 21d is connected to the combustor 22. One end of the combustion exhaust gas pipe 21e is connected to the combustor 22, and the other end of the combustion exhaust gas pipe 21e is connected to the oxygen recovery system 70.

[0016] The combustor 22 receives a supply of generated hydrogen (hydrogen for combustion) contained in the hydrogen electrode off-gas and the oxygen electrode off-gas as combustible gases, and burns these mixed gases. Although not shown in the figure, the combustor 22 is equipped with an ignition device for igniting the mixed gas and a temperature sensor for detecting the internal temperature. The electrolytic cell stack 21 is heated by the combustion heat and combustion exhaust gas generated in the combustor 22. The combustion exhaust gas is discharged into the combustion exhaust gas piping 21e, where it exchanges heat with water vapor flowing through the hydrogen electrode inlet piping 21a and gas flowing through the oxygen electrode inlet piping 21b via the fuel preheater 24 and heat exchanger 27, before being discharged outside the electrolytic module 20. The combustion exhaust gas discharged outside the electrolytic module 20 is then supplied to the oxygen recovery system 70.

[0017] The steam supply system 30 generates steam from raw water (pure water) and supplies it to the electrolytic module 20. The steam supply system 30 comprises a steam supply pipe 31 with one end connected to the hydrogen electrode inlet pipe 21a, a steam generator 32 connected to the other end of the steam supply pipe 31 which evaporates raw water to generate steam, water tanks 33 and 34 for storing raw water, and a water pump 35 which supplies the raw water in the water tanks 33 and 34 to the steam generator 32. The steam generated by the steam generator 32 is introduced into the hydrogen electrode inlet pipe 21a via the steam supply pipe 31, where it is heated by heat exchange with the hydrogen electrode off-gas in a heat exchanger 26 installed in the hydrogen electrode inlet pipe 21a, and further heated by heat exchange with combustion heat from the combustor 22 and combustion exhaust gas in a fuel preheater 24 installed downstream of the heat exchanger 26 in the hydrogen electrode inlet pipe 21a, before being supplied to the hydrogen electrode of the electrolytic cell stack 21.

[0018] The air supply system 50 includes an air supply pipe 51, one end of which is connected to a filter (not shown) and the other end of which is connected to the oxygen electrode inlet pipe 21b; an air blower 52 installed on the air supply pipe 51; and an air supply valve 53 (e.g., a flow control valve) installed upstream of the air blower 52 in the air supply pipe 51. By opening the air supply valve 53 and driving the air blower 52, air is drawn into the air supply pipe 51 via the filter, and the drawn-in air is introduced into the oxygen electrode inlet pipe 21b of the electrolytic module 20. The air introduced into the oxygen electrode inlet pipe 21b is then heated by heat exchange with combustion exhaust gas in a heat exchanger 27 installed on the oxygen electrode inlet pipe 21b, and further heated by heat exchange with hydrogen electrode off-gas in a heat exchanger 25 installed downstream of the heat exchanger 27 on the oxygen electrode inlet pipe 21b, before being supplied to the oxygen electrode of the electrolytic cell stack 21.

[0019] The hydrogen recovery system 60 recovers hydrogen from the hydrogen electrode off-gas, which contains generated hydrogen and unreacted water vapor discharged from the hydrogen electrode outlet. The hydrogen recovery system 60 comprises a hydrogen tank 61 for storing hydrogen, a hydrogen recovery pipe 63 connected to the electrolysis module 20 (hydrogen electrode outlet pipe 21c) and the hydrogen tank 61, and a condenser 62 installed in the hydrogen recovery pipe 63. A booster 64 is installed in the hydrogen recovery pipe 63. In the condenser 62, the hydrogen electrode off-gas, which contains generated hydrogen and water vapor, is separated into gas-liquid and gas-liquid components by heat exchange with cooling water, causing the water vapor in the hydrogen electrode off-gas to condense. The generated hydrogen then passes through the hydrogen recovery pipe 63, is pressurized by the booster 64, and recovered in the hydrogen tank 61. The condensed water is stored in the water tank 33. The water stored in the water tank 33 is used as raw water to generate water vapor for electrolysis.

[0020] The hydrogen supply system 40 includes an oxidation-preventing hydrogen supply pipe 41 that branches off from the downstream side of the condenser 62 in the hydrogen recovery piping 63 and is connected to the hydrogen electrode inlet piping 21a of the electrolytic module 20, and a hydrogen blower 42 installed on the oxidation-preventing hydrogen supply pipe 41. A portion of the hydrogen electrode off-gas (generated hydrogen) that passes through the condenser 62 and flows through the hydrogen recovery piping 63 is supplied to the hydrogen electrode of the electrolytic cell stack 21 as oxidation-preventing hydrogen via the oxidation-preventing hydrogen supply pipe 41 by the operation of the hydrogen blower 42. A hydrogen tank 61 is also connected to the oxidation-preventing hydrogen supply pipe 41. By opening an on-off valve (not shown) installed at the outlet of the hydrogen tank 61 and driving the hydrogen blower 42, the hydrogen in the hydrogen tank 61 can be supplied to the hydrogen electrode of the electrolytic cell stack 21 as oxidation-preventing hydrogen.

[0021] The hydrogen supply system 40 also includes a combustion hydrogen supply pipe 43 that branches off from the downstream side of the condenser 62 in the hydrogen recovery piping 63 and is connected to the combustor 22, and a hydrogen blower 44 installed in the combustion hydrogen supply pipe 43. The remaining portion of the hydrogen electrode off-gas (generated hydrogen) that passes through the condenser 62 and flows through the hydrogen recovery piping 63 is supplied to the combustor 22 as combustion hydrogen via the combustion hydrogen supply pipe 43 by the driving of the hydrogen blower 44.

[0022] The oxygen recovery system 70 recovers oxygen from the combustion exhaust gas containing water vapor and generated oxygen discharged from the combustor 22. The oxygen recovery system 70 includes an oxygen tank 71 for storing oxygen, an oxygen recovery pipe 73 connected to the electrolysis module 20 (combustion exhaust gas pipe 21e) and the oxygen tank 71, and a condenser 72 installed in the oxygen recovery pipe 73. A booster 74 is installed on the downstream side of the condenser 72 in the oxygen recovery pipe 73, and an oxygen recovery valve 73a (for example, an on-off valve) is installed between the condenser 72 and the booster 74 in the oxygen recovery pipe 73. The combustion exhaust gas containing water vapor and generated oxygen is heat-exchanged with cooling water in the condenser 72, so that the water vapor in the combustion exhaust gas is condensed and gas-liquid separated into generated oxygen and condensed water. Then, the generated oxygen is pressurized and recovered into the oxygen tank 71 by opening the oxygen recovery valve 73a and driving the booster 74. Also, the condensed water is stored in the water tank 34. The water stored in the water tank 34 is used as raw water for generating electrolysis water vapor.

[0023] Also, the oxygen recovery system 70 includes a reflux oxygen pipe 75 that branches from the downstream side of the condenser 72 and the upstream side of the oxygen recovery valve 73a in the oxygen recovery pipe 73 and is connected between the air blower 52 and the air supply valve 53 in the air supply pipe 51, a reflux oxygen supply valve 76 (for example, an on-off valve or a flow rate adjustment valve) installed in the reflux oxygen pipe 75, and an oxygen concentration meter 86 installed on the upstream side of the reflux oxygen supply valve 76 in the reflux oxygen pipe 75. A part of the combustion exhaust gas (generated oxygen) flowing through the oxygen recovery pipe 73 after passing through the condenser 72 is supplied as a sweep gas to the oxygen electrode of the electrolysis cell stack 21 through the air supply pipe 51 by opening the reflux oxygen supply valve 76 and driving the air blower 52.

[0024] Furthermore, the oxygen recovery system 70 includes an exhaust pipe 77 that branches from the upstream side of the reflux oxygen supply valve 76 and the downstream side of the oxygen concentration meter 86 in the reflux oxygen pipe 75, and an exhaust valve 77a (e.g., an on-off valve) installed in the exhaust pipe 77. By closing the oxygen recovery valve 73a and the reflux oxygen supply valve 76 and opening the exhaust valve 77a, the combustion exhaust gas that has passed through the condenser 72 can be discharged to the outside air without being refluxed to the air supply pipe 51 side.

[0025] The control device 80 is configured as a microprocessor centered around the CPU 81. In addition to the CPU 81, it includes a ROM 82 that stores processing programs, a RAM 83 that temporarily stores data, and an input / output port (not shown). Detection signals from a flow sensor (not shown) that detects the flow rate of antioxidant hydrogen flowing through the antioxidant hydrogen supply pipe 41, a flow sensor (not shown) that detects the flow rate of combustion hydrogen flowing through the combustion hydrogen supply pipe 43, a flow sensor (not shown) that detects the flow rate of the sweep gas (air or reflux oxygen) flowing through the air supply pipe 51, a temperature sensor 85 installed near the electrolytic cell stack 21 that detects the temperature of the electrolytic cell stack 21 (stack temperature Tst), an oxygen concentration meter 86 that detects the oxygen concentration of the gas (reflux oxygen) flowing through the reflux oxygen pipe 75, etc. are input via the input port. On the other hand, control signals from the control device 80 are output via the output port to the power supply device 29, hydrogen blowers 42, 44, air blower 52, air supply valve 53, oxygen recovery valve 73a, reflux oxygen supply valve 76, exhaust valve 77a, pressure boosters 64, 74, etc.

[0026] Next, the operation of the electrolysis system 10 of this embodiment configured in this way will be described. FIG. 2 is a flowchart showing an example of the control process executed by the CPU 81 of the control device 80. This process is executed when the start of the electrolysis system 10 is requested from the upper system.

[0027] When the control process is executed, the CPU 81 of the control device 80 first opens the air supply valve 53 and the exhaust valve 77a, and closes the oxygen recovery valve 73a and the recirculating oxygen supply valve 76 (S100). Next, the CPU 81 controls the hydrogen blowers 42, 44 and the air blower 52 so that combustion hydrogen is supplied from the hydrogen tank 61 to the combustor 22 via the hydrogen electrode and condenser 62 of the electrolytic cell stack 21, and air is supplied from the air supply system 50 to the combustor 22 via the oxygen electrode of the electrolytic cell stack 21 (S102). Then, the CPU 81 drives the ignition device to ignite the mixture of combustion hydrogen and air in the combustor 22 (S104). As a result, the electrolytic cell stack 21 is warmed up by the combustion heat and combustion exhaust gas generated by the combustion in the combustor 22. During warm-up, the exhaust valve 77a is open and the oxygen recovery valve 73a and the recirculating oxygen supply valve 76 are closed, so the combustion exhaust gas generated by the combustion of the mixed gas of combustion hydrogen and air in the combustor 22 is discharged to the outside air through the exhaust pipe 77. Next, the CPU 81 waits for the stack temperature Tst from the temperature sensor 85 to rise above a predetermined temperature Tref (S106). Here, the predetermined temperature Tref is a threshold value used to determine whether the warm-up of the electrolytic cell stack 21 is complete and the system startup is complete.

[0028] When the CPU 81 determines that the stack temperature Tst has risen above a predetermined temperature Tref, it controls the steam generator 32 and the water pump 35 to start supplying water vapor in addition to hydrogen to the hydrogen electrode of the electrolytic cell stack 21 (S108), and controls the power supply unit 29 to start supplying power to the electrolytic cell stack 21 (S110). This starts the electrolytic operation of the electrolytic cell stack 21. Due to the electrolytic operation of the electrolytic cell stack 21, water vapor is electrolytically decomposed at the hydrogen electrode to produce hydrogen, and hydrogen electrode off-gas containing the produced hydrogen and unreacted water vapor is discharged from the hydrogen electrode. The hydrogen electrode off-gas discharged from the hydrogen electrode passes through the condenser 62, where the water vapor in the hydrogen electrode off-gas is condensed and separated into gas-liquid, produced hydrogen and condensed water. A portion of the hydrogen electrode off-gas (produced hydrogen) that has passed through the condenser 62 is supplied to the hydrogen electrode as hydrogen for oxidation prevention, another portion is supplied to the combustor 22 as hydrogen for combustion, and the remainder is recovered in the hydrogen tank 61. Furthermore, the electrolytic operation of the electrolytic cell stack 21 generates oxygen at the oxygen electrode, and an oxygen electrode off-gas containing the generated oxygen and sweep gas (air) is discharged from the oxygen electrode. The oxygen electrode off-gas discharged from the oxygen electrode is supplied to the combustor 22 as a combustion aid gas and is burned together with the combustion hydrogen supplied to the combustor 22. In the combustor 22, combustion of the combustion hydrogen and the generated oxygen produces a combustion exhaust gas containing water vapor and unburned generated oxygen. The generated combustion exhaust gas then passes through the condenser 72, where the water vapor in the combustion exhaust gas is condensed, and the gas-liquid separation is performed into generated oxygen and condensed water.

[0029] When the electrolysis operation starts, the CPU 81 closes the oxygen recovery valve 73a and keeps the exhaust valve 77a open, while simultaneously closing the air supply valve 53 and opening the recirculating oxygen supply valve 76 (S112). The CPU 81 then controls the air blower 52 based on the oxygen concentration detected by the oxygen concentration meter 86 and the amount of combustion hydrogen supplied, so that the mixed gas of oxygen electrode off-gas supplied from the oxygen electrode of the electrolytic cell stack 21 to the combustor 22 and combustion hydrogen has an oxygen concentration suitable for combustion (S114). As a result, the supply of air to the oxygen electrode of the electrolytic cell stack 21 is stopped, a portion of the combustion exhaust gas discharged from the combustor 22 and passing through the condenser 72 is recirculated to the oxygen electrode of the electrolytic cell stack 21, and the remaining combustion exhaust gas is discharged into the outside air. Immediately after the electrolysis operation starts, the combustion exhaust gas contains residual air (nitrogen) supplied during system startup, and the oxygen concentration in the combustion exhaust gas is relatively low. Therefore, by circulating the combustion exhaust gas between the oxygen electrode of the electrolytic cell stack 21, the combustor 22, and the condenser 72 with the supply of air to the oxygen electrode of the electrolytic cell stack 21 stopped, the oxygen concentration in the combustion exhaust gas that has passed through the condenser 72 can be increased by the oxygen generated at the oxygen electrode. Note that since the oxygen recovery valve 73a is closed, no oxygen is recovered into the oxygen tank 71 at this point.

[0030] The S114 process is performed by setting a target flow rate for reflux gas based on the oxygen concentration detected by the oxygen concentration meter 86 and the amount of combustion hydrogen supplied, and then controlling the air blower 52 so that the reflux gas is supplied to the oxygen electrode of the electrolytic cell stack 21 at the set target flow rate. The control of the air blower 52 can be performed by feedback control based on the target flow rate and the flow rate from a flow sensor (not shown) installed in the air supply pipe 51. This makes it possible to improve the combustion of the mixed gas in the combustor 22 and maintain the temperature inside the electrolytic module 20 at a temperature suitable for electrolytic operation.

[0031] Next, the CPU 81 waits until the oxygen concentration detected by the oxygen concentration meter 86 reaches a predetermined concentration (for example, 99%) or higher (S116). When the CPU 81 determines that the oxygen concentration detected by the oxygen concentration meter 86 has reached a predetermined concentration or higher, it maintains the open state of the recirculating oxygen supply valve 76, slightly opens the air supply valve 53, closes the exhaust valve 77a, opens the oxygen recovery valve 73a, and starts driving the booster 74 (S118), thereby ending the control process. As a result, a portion of the combustion exhaust gas (generated oxygen) that has passed through the condenser 72 is recirculated to the oxygen electrode of the electrolytic cell stack 21, and the remaining combustion exhaust gas (generated oxygen) is recovered in the oxygen tank 71.

[0032] Thus, until the system startup is complete, the electrolytic system 10 warms up the electrolytic cell stack 21 by supplying air as a combustion aid to the combustor 22 via the electrolytic cell stack 21 and burning it with the combustion hydrogen. Once the warming up of the electrolytic cell stack 21 is complete and the electrolytic operation starts, the supply of air to the electrolytic cell stack 21 is stopped, and the generated oxygen produced by the electrolytic operation is circulated internally. This reduces the proportion of nitrogen in the circulating gas compared to supplying air to the electrolytic cell stack 21 during the electrolytic operation. As a result, it is possible to suppress the performance degradation of the electrolytic cell stack 21 and reduce the amount of nitrogen oxides produced in the combustor 22 due to the combustion of the combustion hydrogen and the oxygen electrode off-gas. Furthermore, since the combustion exhaust gas produced in the combustor 22 is passed through the condenser 72 to separate the generated oxygen and water vapor into gas-liquid before being circulated to the electrolytic cell stack 21, the amount of water vapor contained in the oxygen electrode off-gas discharged to the combustor 22 is reduced, further improving the combustibility in the combustor 22. Furthermore, since the generated oxygen is circulated internally and the combustion exhaust gas (generated oxygen) that has passed through the condenser 72 is stored in the oxygen tank 71, high-purity oxygen can be recovered in the oxygen tank 71.

[0033] Furthermore, the electrolysis system 10 passes the hydrogen electrode off-gas discharged from the electrolytic cell stack 21 through the condenser 62 to condense the water vapor in the hydrogen electrode off-gas, and then supplies it to the combustor 22 as combustion hydrogen. This reduces the amount of water vapor contained in the combustion hydrogen, thereby improving the combustibility in the combustor 22.

[0034] In the embodiment described above, the oxygen concentration meter 86 was installed in the reflux oxygen piping 75, but it may also be installed downstream of the condenser 72 and upstream of the branching point to the reflux oxygen piping 75 in the oxygen recovery piping 73.

[0035] The above describes the forms for implementing this disclosure using embodiments, but this disclosure is not limited in any way to these embodiments, and can of course be implemented in various forms without departing from the gist of this disclosure. [Industrial applicability]

[0036] This disclosure can be used in industries such as the manufacturing of electrolytic systems. [Explanation of symbols]

[0037] 10 Electrolysis system, 21 Electrolytic cell stack (electrolytic cell), 22 Combustor (combustion section), 31 Steam supply pipe (steam supply line), 51 Air supply pipe (oxidizer supply line), 52 Air blower (blower), 53 Air supply valve (first supply valve), 71 Oxygen tank, 72 Condenser (condensing section), 73 Oxygen recovery piping (oxygen recovery line), 73a Oxygen recovery valve (recovery valve), 75 Recirculating oxygen piping (recirculation line), 76 Recirculating oxygen supply valve (second supply valve), 77 Exhaust pipe (exhaust line), 77a Exhaust valve, 80 Control unit (control section), 86 Oxygen concentration meter.

Claims

1. An electrolytic cell that generates hydrogen and oxygen by electrolyzing water vapor, A water vapor supply line that supplies the water vapor to the electrolytic cell, An oxidant supply line that supplies oxidant gas to the electrolytic cell, A combustion unit burns hydrogen using the oxygen electrode off-gas containing oxygen discharged from the electrolytic cell as an auxiliary combustion gas, and discharges combustion exhaust gas containing water vapor and unburned oxygen. An oxygen recovery line for recovering oxygen from the combustion exhaust gas, A reflux line that branches off from the oxygen recovery line and is connected to the oxidizing agent supply line, An electrolytic system equipped with the following features.

2. The electrolytic system according to claim 1, The oxygen recovery line is equipped with a condensing unit that condenses the water vapor contained in the combustion exhaust gas to separate it into gas-liquid oxygen and condensed water, The reflux line branches off from downstream of the condensation section of the oxygen recovery line and is connected to the oxidizer supply line. Electrolytic system.

3. An electrolytic system according to claim 1 or 2, A blower installed downstream of the connection point between the oxidizer supply line and the reflux line, A first supply valve is installed upstream of the connection point between the oxidizer supply line and the reflux line, and switches between introducing and shutting off air. A second supply valve installed in the aforementioned return line, When the electrolysis system is started, the control unit controls the blower by opening the first supply valve and closing the second supply valve so that air is supplied to the electrolytic cell, and after the electrolysis system is started and the electrolytic cell has started electrolysis, the control unit controls the blower by closing the first supply valve and opening the second supply valve so that reflux gas returned from the oxygen recovery line is supplied to the electrolytic cell, An electrolytic system equipped with the following features.

4. The electrolytic system according to claim 3, An exhaust line that branches off from the oxygen recovery line or the recirculation line upstream of the second supply valve, An exhaust valve installed in the aforementioned exhaust line, A recovery valve installed downstream of the branching point of the oxygen recovery line with the recirculation line, The system includes an oxygen concentration meter installed in the oxygen recovery line or the reflux line, The control unit opens the exhaust valve and closes the recovery valve from the time the electrolytic system is started until the electrolytic cell starts its electrolytic operation and the oxygen concentration detected by the oxygen concentration meter reaches a predetermined concentration or higher, and after the oxygen concentration reaches the predetermined concentration or higher, it closes the exhaust valve and opens the recovery valve. Electrolytic system.

Images