Hydrogen production system and method for operating the hydrogen production system

Abstract

To provide a hydrogen production system and an operation method of the hydrogen production system capable of suppressing the production cost of hydrogen generated by electrolysis of steam in a solid oxide electrolytic cell (SOEC) and expanding the range of the amount of steam which can be electrolyzed.SOLUTION: A hydrogen production system includes a solid oxide electrolytic cell (SOEC) for electrolysis of steam, a steam generator for heating feed water to generate steam, and a combustor for burning a part of hydrogen included in the steam discharged from the hydrogen electrode of the SOEC. The steam generator is configured such that at least a part of the supply water is heated by heat exchange between at least a part of the supply water and a gas containing combustion gas generated in the combustor to generate at least a part of the steam.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a hydrogen production system and a method of operating a hydrogen production system. [Background technology]

[0002] Patent Document 1 describes a hydrogen production system that produces hydrogen by electrolyzing water vapor in a solid oxide electrolysis cell (SOEC). In this hydrogen production system, water vapor generated in a boiler is heated by heat exchange with gas (containing hydrogen generated by electrolysis of water vapor and unreacted water vapor) discharged from the hydrogen electrode of the SOEC in a heat exchanger, and is then supplied to the hydrogen electrode of the SOEC. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7039504 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the range of the amount of steam that can be electrolyzed in the SOEC is expanded, the equipment such as the boiler and heat exchanger will become larger, which will cause an increase in operating costs. In addition, if the equipment such as the boiler and heat exchanger is designed under the condition of a large amount of steam electrolysis in the SOEC, taking into consideration the response to unsteady operation beyond the normal operating range, it may be over-specified, and under normal operating conditions where the amount of steam electrolysis in the SOEC is less than the design point, the steam may not be consumed, the boiler operating conditions may become inefficient, and operating costs may increase. In addition, during low-load operation, the temperature of the supplied steam may decrease, increasing the electrolysis power, which may increase operating costs.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a hydrogen production system and an operating method for a hydrogen production system that can reduce the production costs of hydrogen produced by electrolysis of water vapor in an SOEC and expand the range of the amount of water vapor that can be electrolyzed. [Means for solving the problem]

[0006] In order to achieve the above object, the hydrogen production system according to the present disclosure includes a solid oxide electrolysis cell (SOEC) that electrolyzes water vapor, a water vapor generator that heats a supply of water to generate the water vapor, and a combustor that combusts a portion of the hydrogen contained in the water vapor discharged from a hydrogen electrode of the SOEC. a water vapor discharge line through which water vapor discharged from the hydrogen electrode flows; a gas discharge line through which exhaust gas discharged from an oxygen electrode of the SOEC flows; an oxygen-containing gas supply line communicating the gas discharge line with the combustor; a gas supply line for supplying an oxygen-containing gas to the oxygen electrode; an exhaust gas recirculation line communicating the gas supply line with the gas discharge line; and a booster for boosting the exhaust gas flowing through the exhaust gas recirculation line. The steam generating device is configured such that at least a portion of the supply water is heated by heat exchange between at least a portion of the supply water and a gas including a combustion gas generated in the combustor, thereby generating at least a portion of the steam. The water vapor generating device includes a main heat exchanger for exchanging heat between the water vapor flowing through the water vapor discharge line and the supply water, the combustor is provided in the water vapor discharge line upstream of the main heat exchanger, and the oxygen-containing gas supply line branches off from the gas discharge line downstream of a position where the exhaust gas recirculation line branches off from the gas discharge line. Is 。 Effect of the Invention

[0007] According to the hydrogen production system disclosed herein, when the amount of heat required to generate water vapor is insufficient, a portion of the hydrogen contained in the water vapor discharged from the hydrogen electrode is combusted in a combustor, and the generated gas containing combustion gas is heat exchanged with at least a portion of the supply water, thereby increasing the amount of water vapor generated. This reduces the production cost of hydrogen generated by electrolysis of water vapor in the SOEC and expands the range of amounts of water vapor that can be electrolyzed. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating the configuration of a hydrogen production system according to a first embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic diagram illustrating a configuration of a modified example of the hydrogen production system according to the first embodiment of the present disclosure. [Diagram 3] FIG. 4 is a schematic diagram illustrating a configuration of another modified example of the hydrogen production system according to the first embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic diagram illustrating a configuration of yet another modified example of the hydrogen production system according to the first embodiment of the present disclosure. [Diagram 5] FIG. 1 is a schematic diagram illustrating the configuration of a hydrogen production system according to a second embodiment of the present disclosure. [Figure 6] FIG. 11 is a schematic diagram illustrating a configuration of a modified example of the hydrogen production system according to the second embodiment of the present disclosure. [Figure 7] FIG. 11 is a schematic diagram illustrating a configuration of another modified example of the hydrogen production system according to the second embodiment of the present disclosure. [Figure 8] FIG. 11 is a schematic diagram illustrating a configuration of yet another modified example of the hydrogen production system according to the second embodiment of the present disclosure. [Figure 9] FIG. 11 is a schematic diagram illustrating a configuration of yet another modified example of the hydrogen production system according to the second embodiment of the present disclosure. [Figure 10] FIG. 11 is a schematic diagram illustrating a configuration of yet another modified example of the hydrogen production system according to the second embodiment of the present disclosure. [Figure 11] FIG. 1 is a schematic diagram illustrating the configuration of a hydrogen production system according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a hydrogen production system according to an embodiment of the present disclosure will be described with reference to the drawings. The embodiment described below shows one aspect of the present disclosure, and does not limit the present disclosure. The embodiment can be modified as desired within the scope of the technical concept of the present disclosure.

[0010] (Embodiment 1) <Configuration of hydrogen production system according to embodiment 1 of the present disclosure> 1, a hydrogen production system 1 according to a first embodiment of the present disclosure includes a solid oxide electrolysis cell (SOEC) 2 that electrolyzes water vapor, a power supply device 3 that applies a voltage to the SOEC 2, and a water vapor generator 5 that generates water vapor to be supplied to the SOEC 2. The water vapor generator 5 includes a main heat exchanger 5a, which is, for example, a boiler.

[0011] The SOEC 2 includes a hydrogen electrode 2a, an oxygen electrode 2b, and a solid electrolyte 2c provided between the hydrogen electrode 2a and the oxygen electrode 2b. Although only one SOEC 2 is illustrated in Fig. 1, a configuration in which a plurality of SOECs 2 are housed in the housing 6 may also be used. The power supply device 3 is configured to apply a voltage between the hydrogen electrode 2a and the oxygen electrode 2b.

[0012] The hydrogen electrode 2a is connected to a water vapor supply line 10 that communicates between the hydrogen electrode 2a and the main heat exchanger 5a, and a water vapor discharge line 11 through which water vapor discharged from the hydrogen electrode 2a flows. One end of a water supply line 18 that supplies water to the main heat exchanger 5a is connected to the main heat exchanger 5a, and the other end of the water supply line 18 is connected to a water supply source 12. A pump 13 is provided on the water supply line 18. The main heat exchanger 5a is configured to perform heat exchange between supply water supplied from the water supply source 12 via the water supply line 18 and water vapor flowing through the water vapor discharge line 11.

[0013] The water vapor discharge line 11 is provided with a combustor 19. As described below, the water vapor flowing through the water vapor discharge line 11 contains hydrogen, and the combustor 19 is for burning a part of the hydrogen contained in the water vapor flowing through the water vapor discharge line 11. For this reason, an oxygen-containing gas supply line 17 for supplying an oxygen-containing gas such as air to the combustor 19 is connected to the combustor 19. A condenser 14 may be provided in the water vapor discharge line 11 downstream of the main heat exchanger 5a.

[0014] The oxygen electrode 2b is connected to a gas supply line 20 through which an oxygen-containing gas, such as air, supplied to the oxygen electrode 2b flows, and a gas discharge line 21 through which exhaust gas discharged from the oxygen electrode 2b flows. A compressor 22 for compressing air is provided in the gas supply line 20, and a power turbine 23 driven by the exhaust gas discharged from the oxygen electrode 2b is provided in the gas discharge line 21.

[0015] <Operation of the hydrogen production system according to the first embodiment of the present disclosure> Next, the operation of the hydrogen production system 1 according to the first embodiment of the present disclosure will be described. Supply water supplied from a water supply source 12 is pressurized by a pump 13, flows through a water supply line 18, and is heated in the main heat exchanger 5a to become water vapor. The water vapor generated in the main heat exchanger 5a flows through a water vapor supply line 10 and flows into the hydrogen electrode 2a. Meanwhile, air compressed by a compressor 22 flows through a gas supply line 20 and flows into the oxygen electrode 2b.

[0016] When the power supply 3 applies a voltage between the hydrogen electrode 2a and the oxygen electrode 2b, the water vapor in the hydrogen electrode 2a is electrolyzed into hydrogen and oxygen ions (O 2- ) are produced (see reaction formula (1) below). The oxygen ions pass through the solid electrolyte 2c and become oxygen at the oxygen electrode 2b (see reaction formula (2) below). The water vapor discharged from the hydrogen electrode 2a contains hydrogen produced by electrolysis, and the water vapor containing hydrogen flows through the water vapor discharge line 11. The exhaust gas discharged from the oxygen electrode 2b flows through the gas discharge line 21 and enters the power turbine 23 to drive the power turbine 23. H2O+2e - →H2+O 2- (1) 2O 2- →O2+4e - (2)

[0017] The water vapor (containing hydrogen) discharged from the hydrogen electrode 2a flows through the water vapor discharge line 11 and exchanges heat with the supply water pressurized by the pump 13 in the main heat exchanger 5a. In the main heat exchanger 5a, the supply water is heated to become water vapor, and the water vapor discharged from the hydrogen electrode 2a is cooled. The water vapor discharged from the main heat exchanger 5a flows through the water vapor discharge line 11 and flows into the condenser 14. In the condenser 14, the water vapor is condensed into water, and the water and hydrogen are separated into gas and liquid. The water condensed in the condenser 14 is discharged or reused in an arbitrary device, and the hydrogen is sent to a hydrogen consumption device or a hydrogen storage device (not shown).

[0018] In the main heat exchanger 5a, when the amount of steam electrolyzed in the SOEC2 is increased by only exchanging heat between the water supplied from the water supply source 12 and the steam discharged from the hydrogen electrode 2a, the amount of heat required to generate steam in the main heat exchanger 5a may be insufficient. In such a case, in the first embodiment, a part of hydrogen contained in the steam discharged from the hydrogen electrode 2a is burned in the combustor 19. The temperature of the steam containing the combustion gas generated by the combustion of hydrogen in the combustor 19 increases due to the combustion heat of hydrogen. Therefore, compared with the case where hydrogen is not burned in the combustor 19, the steam supplied to the main heat exchanger 5a becomes high in temperature, and the amount of steam generated by heat exchange with the water supplied to the main heat exchanger 5a can be increased. This makes it possible to supply the necessary amount of steam in the SOEC2. The temperature of the steam discharged from the combustor 19 can be adjusted by adjusting the amount of air supplied through the oxygen-containing gas supply line 17.

[0019] In this way, when the amount of heat required to generate steam in the steam generation device 5 is insufficient, a portion of the hydrogen contained in the steam discharged from the hydrogen electrode 2a is combusted in the combustor 19, and the amount of steam generated can be increased by heat exchanging the generated gas containing combustion gas with the supply water. This suppresses increases in the cost of the steam generation device in the SOEC2, such as the addition of an electric boiler, and expands the range of amounts of steam that can be electrolyzed.

[0020] <Modifications of the hydrogen production system according to the first embodiment of the present disclosure> In the first embodiment, the source of the oxygen-containing gas supplied to the combustor 19 is not specified. However, a compressor may be provided in the oxygen-containing gas supply line 17, and the compressor may be driven to supply air in the atmosphere to the combustor 19. Alternatively, the oxygen-containing gas may be supplied to the combustor 19 from a storage tank for the oxygen-containing gas or a production device for the oxygen-containing gas. As shown in FIG. 2, the oxygen-containing gas supply line 17 may be provided to communicate the gas exhaust line 21 with the combustor 19, and a part of the exhaust gas discharged from the oxygen electrode 2b may be supplied to the combustor 19 as the oxygen-containing gas. According to the configuration of FIG. 2, high-temperature exhaust gas (approximately the same temperature as water vapor) can be used as the oxygen-containing gas, so that the amount of hydrogen consumed in the combustor 19 to obtain the amount of heat required to generate water vapor can be reduced, and as a result, the cost of producing hydrogen in the hydrogen production system 1 can be reduced.

[0021] 3, in order to circulate a part of the exhaust gas discharged from the oxygen electrode 2b to the oxygen electrode 2b, an exhaust gas recirculation line 24 that communicates the gas supply line 20 with the gas discharge line 21 is provided and a booster 25 is provided in the exhaust gas recirculation line 24. In this case, the oxygen-containing gas supply line 17 may be configured to branch off from the gas discharge line 21 downstream of a position A where the exhaust gas recirculation line 24 branches off from the gas discharge line 21. With this configuration, the exhaust gas can be supplied to the combustor 19 while suppressing the effect on the exhaust gas circulation system (specifically, the exhaust gas flowing through the exhaust gas recirculation line 24).

[0022] Also, as shown in FIG. 4, the oxygen-containing gas supply line 17 may be configured to branch off from the exhaust gas recirculation line 24 downstream of the booster 25. According to this configuration, the exhaust gas pressurized by the booster 25 is supplied to the combustor 19, so there is no need to provide a compressor in the oxygen-containing gas supply line 17 to supply the exhaust gas to the combustor 19. Also, when a heat exchanger 26 for recovering heat from the exhaust gas is provided in the exhaust gas recirculation line 24 downstream of the booster 25, the oxygen-containing gas supply line 17 may be configured to branch off from the exhaust gas recirculation line 24 between the booster 25 and the heat exchanger 26. According to this configuration, the exhaust gas before being cooled in the heat exchanger 26 can be supplied to the combustor 19, so that the amount of hydrogen consumed in the combustor 19 can be suppressed. The heat exchanger 26 can also be used in the same manner as the first heat exchanger 5b shown in FIG. 5 of the second embodiment described later.

[0023] (Embodiment 2) Next, a hydrogen production system according to a second embodiment of the present disclosure will be described. The hydrogen production system according to the second embodiment is different from the first embodiment in that the position of the combustor 19 is changed. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference symbols, and detailed descriptions thereof will be omitted.

[0024] <Configuration of hydrogen production system according to embodiment 2 of the present disclosure> 5, in a hydrogen production system 1 according to a second embodiment of the present disclosure, a combustor 19 is provided in a gas discharge line 21. In order to supply a portion of the water vapor (hydrogen-containing gas) containing hydrogen discharged from the hydrogen electrode 2a to the combustor 19, a hydrogen-containing gas supply line 30 branched off from the water vapor discharge line 11 is connected to the combustor 19.

[0025] In addition to the main heat exchanger 5a, the steam generating device 5 includes a first heat exchanger 5b provided in the gas discharge line 21 downstream of the combustor 19. The first heat exchanger 5b is for exchanging heat between a part of the feed water supplied from the feed water source 12 and the exhaust gas flowing through the gas discharge line 21. A feed water branch line 32 branched from the feed water line 18 downstream of the pump 13 is connected to the first heat exchanger 5b in order to supply a part of the feed water supplied from the feed water source 12 to the first heat exchanger 5b. Steam is generated in the first heat exchanger 5b by an operation to be described later, and a steam line 33 that communicates the first heat exchanger 5b and the steam supply line 10 is provided in order to supply this steam to the steam supply line 10. The other configurations are the same as those of the first embodiment.

[0026] <Operation of the hydrogen production system according to the second embodiment of the present disclosure> Next, the operation of the hydrogen production system 1 according to the second embodiment of the present disclosure will be described. A part of the supply water from the supply water source 12 flows through the water supply branch line 32 and flows into the first heat exchanger 5b, and the rest flows into the main heat exchanger 5a. In the main heat exchanger 5a, as in the first embodiment, the water vapor discharged from the hydrogen electrode 2a exchanges heat with the supply water, whereby the supply water is heated to become water vapor, which is discharged from the main heat exchanger 5a.

[0027] The supply water flowing into the first heat exchanger 5b is heated and becomes water vapor by heat exchange with the exhaust gas discharged from the oxygen electrode 2b and flowing through the gas discharge line 21. After being discharged from the first heat exchanger 5b, this water vapor flows through the water vapor line 33 and flows into the water vapor supply line 10, and is mixed with the water vapor discharged from the main heat exchanger 5a and flows into the hydrogen electrode 2a. The operation of electrolysis of water vapor in the SOEC 2, the operation after the water vapor discharged from the hydrogen electrode 2a exchanges heat with the supply water in the main heat exchanger 5a, and the operation of supplying air to the oxygen electrode 2b are the same as those in the first embodiment.

[0028] In the second embodiment, the operation in the case where the amount of steam supplied to the SOEC2 is increased is different from that in the first embodiment. Next, this operation in the second embodiment will be described. In the case where the amount of steam is increased, in the second embodiment, the hydrogen in the steam supplied to the combustor 19 via the hydrogen-containing gas supply line 30 is burned in the combustor 19 using the oxygen in the exhaust gas flowing through the gas exhaust line 21. Since the supplied steam has a temperature similar to that of the exhaust gas, the temperature of the exhaust gas (combustion exhaust gas) generated by the combustion of hydrogen in the combustor 19 increases due to the combustion heat of hydrogen. Therefore, compared to the case where hydrogen is not combusted in the combustor 19, the exhaust gas supplied to the first heat exchanger 5b has a high temperature, and the amount of steam generated by heat exchange with the supply water supplied to the first heat exchanger 5b can be increased. This makes it possible to supply the necessary amount of steam in the SOEC2. The temperature of the exhaust gas discharged from the combustor 19 can be adjusted by adjusting the amount of steam supplied via the hydrogen-containing gas supply line 30.

[0029] In this way, in the second embodiment, as in the first embodiment, a wide range of amounts of water vapor that can be electrolyzed in the SOEC 2 can be covered. However, in the first embodiment, an oxygen-containing gas is supplied to the water vapor discharged from the hydrogen electrode 2a, which may reduce the purity of the product hydrogen in the hydrogen production system 1. In contrast, in the second embodiment, water vapor extracted from the water vapor flowing through the water vapor discharge line 11 is supplied to the combustor 19, so that the oxygen-containing gas is not supplied to the water vapor flowing through the water vapor discharge line 11, thereby preventing a reduction in the purity of the product hydrogen in the hydrogen production system 1.

[0030] <Modification of the hydrogen production system according to the second embodiment of the present disclosure> As shown in FIG. 6, as a part of the configuration of the steam generator 5, a second heat exchanger 5c for exchanging heat between a part of the supply water supplied from the water supply source 12 and the exhaust gas flowing through the gas exhaust line 21 may be further provided in the gas exhaust line 21 upstream of the combustor 19. FIG. 6 illustrates a configuration in which the supply water supplied from the water supply source 12 exchanges heat with the exhaust gas in the first heat exchanger 5b and then exchanges heat with the exhaust gas in the second heat exchanger 5c, but the configuration is not limited to this form. The supply water supplied from the water supply source 12 may exchange heat with the exhaust gas in the second heat exchanger 5c and then exchange heat with the exhaust gas in the first heat exchanger 5b, or the supply water supplied from the water supply source 12 may be split into two flows and then supplied to the first heat exchanger 5b and the second heat exchanger 5c, and the steam generated in the first heat exchanger 5b and the second heat exchanger 5c may flow into the steam supply line 10 after joining together or separately.

[0031] In this configuration, the exhaust gas flowing into the combustor 19 is cooled by heat exchange with water or steam in the second heat exchanger 5c. Therefore, the temperature of the exhaust gas flowing into the combustor 19 is lower than that in the configuration of Fig. 5. If the temperature of the combustion gas generated in the combustor 19 becomes too high, the amount of combustion that can be performed in the combustor 19 is restricted due to the heat resistance of the combustor 19. However, by suppressing the temperature of the exhaust gas flowing into the combustor 19, the amount of combustion that can be performed in the combustor 19 can be increased, and the range of the amount of steam that can be electrolyzed in the SOEC2 can be further expanded.

[0032] 7, in the case where a water vapor recirculation line 34 that communicates the water vapor supply line 10 and the water vapor discharge line 11 is provided and a booster 35 is provided in the water vapor recirculation line 34 for the purpose of circulating a portion of the water vapor discharged from the hydrogen electrode 2a to the hydrogen electrode 2a, the hydrogen-containing gas supply line 30 may be configured to branch off from the water vapor discharge line 11 downstream of a position B where the water vapor recirculation line 34 branches off from the water vapor discharge line 11. With such a configuration, hydrogen contained in the water vapor can be supplied to the combustor 19 without directly affecting the water vapor circulation system (specifically, the water vapor flowing through the water vapor recirculation line 34).

[0033] 8, the hydrogen-containing gas supply line 30 may be configured to branch off from the steam recirculation line 34 downstream of the booster 35. According to this configuration, the steam (hydrogen-containing gas) pressurized by the booster 35 is supplied to the combustor 19, so there is no need to provide a booster in the hydrogen-containing gas supply line 30 to supply hydrogen to the combustor 19.

[0034] 9, in a configuration in which the hydrogen production system 1 includes a low-temperature steam recirculation line 36 that communicates the steam discharge line 11 downstream of the main heat exchanger 5a with the steam supply line 10 or an evaporator (not shown) in the main heat exchanger 5a, and a booster 37 provided in the low-temperature steam recirculation line 36, if the hydrogen-containing gas supply line 30 is configured to branch off from the low-temperature steam recirculation line 36 downstream of the booster 37, the steam pressurized by the booster 37 is supplied to the combustor 19, as in the configuration of FIG. 8, so that it is not necessary to provide a compressor in the hydrogen-containing gas supply line 30 to supply the steam to the combustor 19. In addition, compared to the booster 35 in FIG. 8, the booster 37 operates at a low temperature, which allows for a reduction in compression power and a reduction in the cost of the booster body.

[0035] 10, a first flow rate adjustment device 38 may be provided for adjusting the flow rate of the supply water supplied from the supply water source 12 to the main heat exchanger 5a and the flow rate of the supply water flowing through the branched water supply line 32. The configuration of the first flow rate adjustment device 38 is not particularly limited, and may be, for example, a flow rate adjustment valve 38a provided in the branched water supply line 32. When the first flow rate adjustment device 38 is a flow rate adjustment valve, the flow rate adjustment valve may be provided in the supply water line 18 downstream of the position where the branched water supply line 32 branches off from the supply water line 18, instead of in the branched water supply line 32, or a flow rate adjustment valve may be provided in each of the branched water supply line 32 and the supply water line 18.

[0036] According to this configuration, by adjusting the opening degree of the flow rate control valve 38a, the flow rate of the supply water supplied to the main heat exchanger 5a and the flow rate of the supply water flowing through the water supply branch line 32 are each adjusted, and the amount of water vapor generated in each of the main heat exchanger 5a and the first heat exchanger 5b can be adjusted. As a result, it is possible to appropriately supply the amount of water vapor required for electrolysis of water vapor in the SOEC 2 even during low load or load fluctuation while making maximum use of the surplus heat generated in the hydrogen production system 1. In addition, when the first flow rate control device 38 is provided, a mechanism for adjusting the flow rate of the supply water supplied to the main heat exchanger 5a may be provided, and this mechanism may adjust the flow rate of the supply water to a flow rate required for the operation of the hydrogen production system 1. This makes it possible to individually adjust the amount of water vapor generated in the main heat exchanger 5a and the first heat exchanger 5b. Note that the configuration of this mechanism is not particularly limited, and for example, when the pump 13 is provided, it may be a device for adjusting the discharge rate of the pump 13.

[0037] 10 shows a configuration in which a first flow rate adjustment device 38 is provided in addition to the configuration of embodiment 2 (FIG. 5), but the present invention is not limited to this configuration. Even if a first flow rate adjustment device 38 is provided in addition to the configuration of each of the modified examples of embodiment 2 (FIGS. 6 to 9), the same action and effect can be obtained by the same operation.

[0038] (Embodiment 3) Next, a hydrogen production system according to a third embodiment of the present disclosure will be described. In the hydrogen production system according to the third embodiment, in comparison with the first embodiment, the steam generation device 5 includes a superheater for superheating the generated steam, and the combustion heat generated in the combustor is used as the heat source for the superheater. In the first embodiment, the same components as those in the first embodiment are given the same reference symbols, and detailed descriptions thereof will be omitted. Furthermore, as long as there is no contradiction in the configuration, the configuration of the modified example described in the first embodiment can also be applied to the third embodiment.

[0039] <Configuration of hydrogen production system according to embodiment 3 of the present disclosure> As shown in FIG. 11, in a hydrogen production system 1 according to a third embodiment of the present disclosure, a steam generator 5 includes a main heat exchanger 5a and a superheater 5d in which steam generated in the main heat exchanger 5a exchanges heat with combustion gas generated in a combustor 19. A steam extraction line 40 branched from a steam discharge line 11 and an exhaust gas extraction line 41 branched from a gas discharge line 21 are connected to the combustor 19. That is, the steam extraction line 40 communicates the steam discharge line 11 with the combustor 19, and the exhaust gas extraction line 41 communicates the gas discharge line 21 with the combustor 19. The combustor 19 communicates with the superheater 5d via a combustion gas supply line 42, and communicates with the gas discharge line 21 via a combustion gas discharge line 43 downstream of a position C at which the exhaust gas extraction line 41 branches from the gas discharge line 21.

[0040] The water vapor extraction line 40 may be provided with a second flow rate adjustment device 44 that adjusts the flow rate of water vapor flowing through the water vapor extraction line 40. Furthermore, the exhaust gas extraction line 41 may be provided with a third flow rate adjustment device 45 that adjusts the flow rate of exhaust gas flowing through the exhaust gas extraction line 41. The configurations of the second flow rate adjustment device 44 and the third flow rate adjustment device 45 are not particularly limited, and may be, for example, flow rate adjustment valves 44a and 45a. The other configurations are the same as those of the first embodiment.

[0041] <Operation of the hydrogen production system according to the third embodiment of the present disclosure> As in the first embodiment, in the main heat exchanger 5a, the feed water supplied from the feed water source 12 exchanges heat with the steam discharged from the hydrogen electrode 2a, whereby the feed water is heated and becomes steam. The steam discharged from the main heat exchanger 5a is further superheated in the superheater 5d by heat exchange with the combustion gas generated in the combustor 19 through an operation described below, thereby becoming superheated steam. In the third embodiment, the temperature of the steam flowing into the hydrogen electrode 2a can be further increased, so that the operating conditions of the SOEC2 can be maintained within a desired range even during low-load operation.

[0042] In the third embodiment, a part of the steam flowing through the steam exhaust line 11 is supplied to the combustor 19 through the steam extraction line 40, and a part of the exhaust gas flowing through the gas exhaust line 21 is supplied through the exhaust gas extraction line 41, and hydrogen contained in the steam is burned by oxygen contained in the exhaust gas. Since the supplied steam and exhaust gas have approximately the same temperature, the temperature of the combustion gas (combustion exhaust gas) generated by the combustion of hydrogen in the combustor 19 increases due to the combustion of hydrogen. Therefore, the generated combustion gas (combustion exhaust gas) can be superheated by heat exchange with the steam discharged from the main heat exchanger 5a in the superheater 5d, and the amount of steam generated can be increased by heat exchange between the supply water and the main heat exchanger 5a and the superheater 5d. The combustion gas that has exchanged heat with the steam in the superheater 5d flows into the gas exhaust line 21 through the combustion gas exhaust line 43 and is mixed with the exhaust gas flowing through the gas exhaust line 21.

[0043] When the flow rate control valve 44a is provided in the steam extraction line 40, the temperature of the steam flowing into the hydrogen electrode 2a can be controlled to a desired temperature by adjusting the degree of superheat of the steam in the superheater 5d using the flow rate control valve 44a, so that the operating conditions of the SOEC 2 can be maintained in an optimal state. When the flow rate control valve 45a is provided in the exhaust gas extraction line 41 in addition to the flow rate control valve 44a, the temperature of the steam flowing into the hydrogen electrode 2a can be further easily controlled by adjusting the degree of superheat of the steam in the superheater 5d using the flow rate control valves 44a and 45a, so that stable operation can be achieved even in a wider operating range of the SOEC 2.

[0044] (Relationship between the steam generating device and the combustor of the present disclosure) In the present disclosure, in the first embodiment, the steam generator 5 includes a main heat exchanger 5a, and in the main heat exchanger 5a, the supply water supplied from the water supply source 12 exchanges heat with the steam containing the combustion gas generated in the combustor 19, thereby heating the supply water and generating steam. In the second embodiment, the steam generator 5 includes a main heat exchanger 5a and a first heat exchanger 5b, or a main heat exchanger 5a, a first heat exchanger 5b, and a second heat exchanger 5c, and in the first heat exchanger 5b and the second heat exchanger 5c, a part of the supply water supplied from the water supply source 12 exchanges heat with the exhaust gas containing the combustion gas generated in the combustor 19 that combusts a part of the hydrogen contained in the steam discharged from the hydrogen electrode 2a, thereby heating the supply water and generating steam. In the third embodiment, the steam generator 5 includes a main heat exchanger 5a and a superheater 5d, and in the superheater 5d, the steam discharged from the main heat exchanger 5a exchanges heat with the combustion gas generated in the combustor 19 that burns a portion of the hydrogen contained in the steam discharged from the hydrogen electrode 2a, whereby the steam is further superheated and superheated steam that flows into the hydrogen electrode 2a is generated. According to the first to third embodiments, the steam generator 5 is configured to heat at least a portion of the supply water (including the steam generated in the main heat exchanger 5a) to generate at least a portion of the steam by heat exchange between at least a portion of the supply water and the gas containing the combustion gas generated in the combustor 19 that burns a portion of the hydrogen contained in the steam discharged from the hydrogen electrode 2a, thereby increasing the overall amount of steam generated.

[0045] The contents described in each of the above embodiments can be understood, for example, as follows.

[0046] [1] A hydrogen production system according to one embodiment includes: A solid oxide electrolysis cell (SOEC) (2) that electrolyzes water vapor; A steam generator (5) for heating supply water to generate the steam; a combustor (19) for burning a portion of hydrogen contained in the water vapor discharged from the hydrogen electrode (2a) of the SOEC (2); Equipped with The water vapor generating device (5) is configured so that at least a portion of the supply water is heated by heat exchange between at least a portion of the supply water and a gas including the combustion gas generated in the combustor (19), thereby generating at least a portion of the water vapor.

[0047] According to the hydrogen production system disclosed herein, when the amount of heat required to generate water vapor is insufficient, a portion of the hydrogen contained in the water vapor discharged from the hydrogen electrode is combusted in a combustor, and the generated gas containing combustion gas is heat exchanged with at least a portion of the supply water, thereby increasing the amount of water vapor generated. This reduces the production cost of hydrogen generated by electrolysis of water vapor in the SOEC and expands the range of amounts of water vapor that can be electrolyzed.

[0048] [2] A hydrogen production system according to another embodiment is the hydrogen production system according to [1], a water vapor discharge line (11) through which water vapor discharged from the hydrogen electrode (2a) flows, The water vapor generating device (5) includes a main heat exchanger (5a) for exchanging heat between the water vapor flowing through the water vapor discharge line (11) and the supply water, The combustor (19) is provided on the water vapor discharge line (11) upstream of the main heat exchanger (5a).

[0049] According to this configuration, when the amount of heat required to generate steam is insufficient, the supply water is further heated by heat exchange between the supply water and the gas containing the combustion gas generated in the combustor, thereby increasing the amount of steam generated, thereby expanding the range of the amount of steam that can be electrolyzed in the SOEC.

[0050] [3] A hydrogen production system according to yet another embodiment is the hydrogen production system according to [2], a gas exhaust line (21) through which exhaust gas discharged from the oxygen electrode (2b) of the SOEC (2) flows; an oxygen-containing gas supply line (17) communicating between the gas exhaust line (21) and the combustor (19); Equipped with.

[0051] With this configuration, high-temperature exhaust gas can be used as the oxygen-containing gas necessary for burning hydrogen, thereby reducing the amount of hydrogen consumed in the combustor to obtain the heat required to generate water vapor, and as a result, reducing the cost of producing hydrogen in the hydrogen production system.

[0052] [4] A hydrogen production system according to yet another embodiment is the hydrogen production system according to [3], a gas supply line (20) for supplying an oxygen-containing gas to the oxygen electrode (2b); an exhaust gas recirculation line (24) communicating between the gas supply line (20) and the gas discharge line (21); a booster (25) for boosting the pressure of the exhaust gas flowing through the exhaust gas recirculation line (24); Equipped with The oxygen-containing gas supply line (17) branches off from the gas discharge line (21) downstream of a position (A) at which the exhaust gas recirculation line (24) branches off from the gas discharge line (21).

[0053] With this configuration, the higher temperature exhaust gas can be stably used in the combustor as the oxygen-containing gas necessary for burning hydrogen, even at low loads or during load fluctuations, thereby reducing the amount of hydrogen consumed in the combustor to obtain the heat required to generate water vapor, and as a result, reducing the cost of producing hydrogen in the hydrogen production system.

[0054] [5] A hydrogen production system according to yet another embodiment is the hydrogen production system according to [3], a gas supply line (20) for supplying an oxygen-containing gas to the oxygen electrode (2b); an exhaust gas recirculation line (24) communicating between the gas supply line (20) and the gas discharge line (21); a booster (25) for boosting the pressure of the exhaust gas flowing through the exhaust gas recirculation line (24); Equipped with The oxygen-containing gas supply line (17) branches off from the exhaust gas recirculation line (24) downstream of the booster (25).

[0055] With this configuration, even if it is necessary to boost the pressure of the oxygen-containing gas required to burn hydrogen to a pressure higher than the pressure in the gas exhaust line when supplying it to the combustor, there is no need to install a separate booster to boost the pressure of the oxygen-containing gas, and the exhaust gas can be supplied to the combustor as oxygen-containing gas boosted by a booster installed in the exhaust gas recirculation line, thereby reducing the cost of producing hydrogen in the hydrogen production system.

[0056] [6] A hydrogen production system according to yet another embodiment is the hydrogen production system according to [1], a water vapor discharge line (11) through which water vapor discharged from the hydrogen electrode (2a) flows; a gas exhaust line (21) through which exhaust gas discharged from the oxygen electrode (2b) of the SOEC (2) flows; Equipped with the water vapor generating device (5) further includes a first heat exchanger (5b) for exchanging heat between at least a part of the supply water and the exhaust gas discharged from the oxygen electrode (2b); the combustor (19) is provided in the gas discharge line (21) upstream of the first heat exchanger (5b), The combustor (19) communicates with the water vapor exhaust line (11) through a hydrogen-containing gas supply line (30).

[0057] In the configurations [2] to [5], the oxygen-containing gas is supplied to the water vapor discharged from the hydrogen electrode, which may reduce the purity of the product hydrogen in the hydrogen production system. In contrast, in the configuration [4], the water vapor containing hydrogen extracted from the water vapor flowing through the water vapor discharge line is supplied to the combustor, so that the oxygen-containing gas is not supplied to the water vapor flowing through the water vapor discharge line, which prevents the purity of the product hydrogen in the hydrogen production system from decreasing.

[0058] [7] A hydrogen production system according to yet another embodiment is the hydrogen production system according to [6], the steam generation device (5) further includes a second heat exchanger (5c) provided in the gas discharge line (21) upstream of the combustor (19), The first heat exchanger (5b) and the second heat exchanger (5c) are each configured to perform heat exchange between at least a part of the supply water and the exhaust gas flowing through the gas exhaust line.

[0059] According to this configuration, the exhaust gas is cooled by the heat exchange between the exhaust gas and the supply water in the second heat exchanger, and the temperature of the exhaust gas flowing into the combustor is lower than that of the configuration [6]. If the temperature of the combustion gas generated in the combustor becomes too high, the amount of combustion that can be performed in the combustor is restricted due to the heat resistance of the combustor. However, by lowering the temperature of the exhaust gas flowing into the combustor, the amount of combustion that can be performed in the combustor can be increased, so the amount of water vapor generated can be increased, and the range of the amount of water vapor that can be electrolyzed in the SOEC can be further expanded.

[0060] [8] A hydrogen production system according to yet another embodiment is the hydrogen production system according to [6], The water vapor generating device (5) includes a main heat exchanger (5a) for exchanging heat between at least a part of the supply water and water vapor flowing through the water vapor discharge line (11), The hydrogen production system (1) comprises: a water supply line (18) for supplying the supply water to the main heat exchanger (5a); a water supply branch line (32) communicating between the water supply line (18) and the first heat exchanger (5b); a steam supply line (10) communicating between the main heat exchanger (5a) and the hydrogen electrode (2a); a water vapor line (33) communicating between the first heat exchanger (5b) and the water vapor supply line (10); a first flow rate adjustment device (38) that adjusts the flow rate of the supply water supplied to the main heat exchanger (5a) and the flow rate of the supply water flowing through the water supply branch line (32); Equipped with.

[0061] With this configuration, the amount of heat being applied to the supply water in each of the main heat exchanger and the first heat exchanger can be adjusted. This makes it possible to maximize the use of surplus heat generated in the hydrogen production system while expanding the range of the amount of steam that can be electrolyzed in the SOEC, making it possible to secure steam even if the amount of steam required for electrolysis increases.

[0062] [9] A hydrogen production system according to yet another embodiment is the hydrogen production system according to [7], The water vapor generating device (5) includes a main heat exchanger (5a) for exchanging heat between at least a part of the supply water and water vapor flowing through the water vapor discharge line (11), The hydrogen production system (1) comprises: a water supply line (18) for supplying the supply water to the main heat exchanger (5a); a water supply branch line (32) communicating the water supply line (18) with both the first heat exchanger (5b) and the second heat exchanger (5c); a water vapor line (33) communicating both the first heat exchanger (5b) and the second heat exchanger (5c) with the water vapor supply line (10); a first flow rate adjustment device (38) that adjusts the flow rate of the supply water supplied to the main heat exchanger (5a) and the flow rate of the supply water flowing through the water supply branch line (32); Equipped with.

[0063] According to this configuration, since the amount of heat of the supply water in each of the main heat exchanger, the first heat exchanger, and the second heat exchanger can be adjusted, the range of the amount of steam that can be electrolyzed in the SOEC can be expanded while making maximum use of the excess heat generated in the hydrogen production system operated under a wider range of operating conditions, and it is possible to secure the amount of steam even if the amount of steam required for electrolysis increases. The hydrogen-containing gas supply line (30) may be connected downstream of the branch point (B) of the steam recirculation line (34) connected to the steam discharge line (11) (see FIG. 7), or downstream of the booster (35) of the steam recirculation line (34) (see FIG. 8), or downstream of the booster (37) of the low-temperature steam recirculation line (36) connected downstream of the main heat exchanger (5a) (see FIG. 9).

[0064]

[10] A hydrogen production system according to yet another embodiment is the hydrogen production system according to [1], a water vapor discharge line (11) through which water vapor discharged from the hydrogen electrode (2a) flows; a gas exhaust line (21) through which exhaust gas discharged from the oxygen electrode (2b) of the SOEC (2) flows; a steam extraction line (40) communicating between the steam discharge line (11) and the combustor (19); an exhaust gas extraction line (41) communicating between the gas discharge line (21) and the combustor (19); Equipped with The water vapor generating device (5) a main heat exchanger (5a) in which heat is exchanged between the water vapor flowing through the water vapor discharge line (11) and the supply water; a superheater (5d) in which the steam generated in the main heat exchanger (5a) exchanges heat with the combustion gas generated in the combustor (19); Equipped with.

[0065] According to this configuration, the water vapor generated in the water vapor generator is superheated in the superheater, thereby further increasing the temperature of the water vapor flowing into the hydrogen electrode. Therefore, the operating temperature of the SOEC can be maintained within a desired range even during low-load operation, thereby suppressing increases in operating costs.

[0066]

[11] A hydrogen production system according to yet another embodiment is the hydrogen production system according to

[10] , The steam extraction system further includes a second flow rate adjustment device (44) that is provided in the steam extraction line (40) and adjusts the flow rate of steam flowing through the steam extraction line (40).

[0067] According to this configuration, by adjusting the superheating of the water vapor in the superheater using the second flow control device, it becomes easy to control the temperature of the water vapor flowing into the hydrogen electrode of the SOEC, so that the operating temperature of the SOEC can be maintained within a desired range even during low-load operation, and increases in operating costs can be suppressed.

[0068]

[12] A hydrogen production system according to yet another embodiment is the hydrogen production system according to

[11] , The exhaust gas extraction system includes a third flow rate adjustment device (45) that is provided in the exhaust gas extraction line (41) and adjusts the flow rate of the exhaust gas flowing through the exhaust gas extraction line (41).

[0069] According to this configuration, by adjusting the superheating of the water vapor in the superheater using the second flow control device and the third flow control device, it becomes easier to control the temperature of the water vapor flowing into the hydrogen electrode of the SOEC, thereby enabling stable operation of the SOEC over a wider operating range and suppressing increases in operating costs.

[0070]

[13] A hydrogen production system according to one embodiment includes: A method for operating a hydrogen production system according to [9], comprising the steps of: The method includes adjusting the flow rate of the supply water flowing through the branch water supply line (32) by the first flow rate adjustment device (38).

[0071] According to the operating method of the hydrogen production system disclosed herein, the amount of water vapor generated in each of the main heat exchanger and the first heat exchanger can be adjusted, thereby making it possible to maximize the utilization of surplus heat generated in the hydrogen production system while appropriately supplying the amount of water vapor required for electrolysis in the SOEC, even during low load or load fluctuations.

[0072]

[14] A hydrogen production system according to one embodiment includes: A method for operating a hydrogen production system according to

[11] , comprising the steps of: The method includes adjusting the degree of superheat of the steam in the superheater (5d) by the second flow rate adjustment device (44).

[0073] According to the operating method of the hydrogen production system disclosed herein, the temperature of the water vapor flowing into the hydrogen electrode can be controlled to a desired temperature by adjusting the degree of superheat of the water vapor in the superheater using the second flow control device, thereby maintaining the operating conditions of the SOEC at optimal levels.

[0074]

[15] A hydrogen production system according to one embodiment includes: A method for operating a hydrogen production system according to

[12] , comprising the steps of: The method includes adjusting the degree of superheat of the steam in the superheater (5d) by the second flow rate adjustment device (44) and the third flow rate adjustment device (45).

[0075] According to the operating method of the hydrogen production system disclosed herein, by adjusting the flow rates of the hydrogen gas-containing gas and the oxygen-containing gas to be supplied to the combustor using the second flow control device and the third flow control device in accordance with the degree of superheating of the water vapor to be generated in the superheater, it becomes easier to control the temperature of the water vapor flowing into the hydrogen electrode, thereby enabling stable operation in a wider operating range of the SOEC. [Explanation of symbols]

[0076] 1 Hydrogen production system 2. Solid oxide electrolysis cell (SOEC) 2a Hydrogen electrode 2b Oxygen electrode 5. Steam generator 5a main heat exchanger 5b 1st heat exchanger 5c 2nd heat exchanger 5d superheater 10. Steam supply line 11 Water vapor exhaust line 12 Water supply source 13. Pump 17 Oxygen-containing gas supply line 18 Water Supply Line 19 Combustor 20 Gas supply line 21 Gas exhaust line 24 Exhaust gas recirculation line 25,35,37 Booster 30 Hydrogen-containing gas supply line 32 Water supply branch line 33 Steam Line 38 1st flow control device 40 Steam extraction line 41 Exhaust gas extraction line 44 2nd flow control device 45 3rd flow control device

Claims

1. a solid oxide electrolysis cell (SOEC) for electrolyzing water vapor; A steam generator for heating supply water to generate the steam; a combustor for combusting a portion of hydrogen contained in the water vapor discharged from the hydrogen electrode of the SOEC; a water vapor discharge line through which water vapor discharged from the hydrogen electrode flows; a gas exhaust line through which exhaust gas discharged from an oxygen electrode of the SOEC flows; an oxygen-containing gas supply line communicating the gas exhaust line with the combustor; a gas supply line for supplying an oxygen-containing gas to the oxygen electrode; an exhaust gas recirculation line communicating between the gas supply line and the gas exhaust line; a booster that boosts the pressure of exhaust gas flowing through the exhaust gas recirculation line; Equipped with the steam generating device is configured to perform heat exchange between at least a portion of the supply water and a gas including the combustion gas generated in the combustor, thereby heating at least a portion of the supply water and generating at least a portion of the steam; The water vapor generating device includes a main heat exchanger that exchanges heat between the water vapor flowing through the water vapor discharge line and the supply water, the combustor is provided in the water vapor discharge line upstream of the main heat exchanger, The hydrogen production system, wherein the oxygen-containing gas supply line branches off from the gas exhaust line downstream of a position where the exhaust gas recirculation line branches off from the gas exhaust line.

2. a solid oxide electrolysis cell (SOEC) for electrolyzing water vapor; A steam generator for heating supply water to generate the steam; a combustor for combusting a portion of hydrogen contained in the water vapor discharged from the hydrogen electrode of the SOEC; a water vapor discharge line through which water vapor discharged from the hydrogen electrode flows; a gas exhaust line through which exhaust gas discharged from an oxygen electrode of the SOEC flows; a gas supply line for supplying an oxygen-containing gas to the oxygen electrode; an exhaust gas recirculation line communicating between the gas supply line and the gas exhaust line; A booster that boosts the pressure of exhaust gas flowing through the exhaust gas recirculation line; an oxygen-containing gas supply line communicating the exhaust gas recirculation line with the combustor; Equipped with the steam generating device is configured to perform heat exchange between at least a portion of the supply water and a gas including the combustion gas generated in the combustor, thereby heating at least a portion of the supply water and generating at least a portion of the steam; The water vapor generating device includes a main heat exchanger that exchanges heat between the water vapor flowing through the water vapor discharge line and the supply water, the combustor is provided in the water vapor discharge line upstream of the main heat exchanger, The hydrogen production system, wherein the oxygen-containing gas supply line branches off from the exhaust gas recirculation line downstream of the booster.

3. a solid oxide electrolysis cell (SOEC) for electrolyzing water vapor; A steam generator for heating supply water to generate the steam; a combustor for combusting a portion of hydrogen contained in the water vapor discharged from the hydrogen electrode of the SOEC; a water vapor discharge line through which water vapor discharged from the hydrogen electrode flows; a gas exhaust line through which exhaust gas discharged from an oxygen electrode of the SOEC flows; Equipped with the water vapor generating device includes a first heat exchanger configured to perform heat exchange between at least a portion of the supply water and a gas including a combustion gas generated in the combustor, thereby heating at least a portion of the supply water and generating at least a portion of the water vapor; The combustor is provided in the gas exhaust line, the combustor communicates with the water vapor exhaust line via a hydrogen-containing gas supply line; The steam generating device further includes a second heat exchanger provided in the gas exhaust line upstream of the combustor, A hydrogen production system configured to perform heat exchange between at least a portion of the supply water and exhaust gas flowing through the gas exhaust line in each of the first heat exchanger and the second heat exchanger.

4. A solid oxide electrolysis cell (SOEC) for electrolyzing water vapor; A steam generator for heating supply water to generate the steam; a combustor for combusting a portion of hydrogen contained in the water vapor discharged from the hydrogen electrode of the SOEC; a water vapor discharge line through which water vapor discharged from the hydrogen electrode flows; a gas exhaust line through which exhaust gas discharged from an oxygen electrode of the SOEC flows; Equipped with The water vapor generating device includes: a main heat exchanger in which at least a portion of the supply water exchanges heat with steam flowing through the steam discharge line; a first heat exchanger configured to perform heat exchange between at least a portion of the supply water and a gas including a combustion gas generated in the combustor, thereby heating at least a portion of the supply water and generating at least a portion of the water vapor; A hydrogen production system comprising: The combustor is provided in the gas exhaust line, the combustor communicates with the water vapor exhaust line via a hydrogen-containing gas supply line; The hydrogen production system includes: a water supply line for supplying the supply water to the main heat exchanger; a water supply branch line communicating the water supply line with the first heat exchanger; a water vapor supply line communicating the main heat exchanger with the hydrogen electrode; a steam line communicating between the first heat exchanger and the steam supply line; a first flow rate adjusting device that adjusts the flow rate of the supply water supplied to the main heat exchanger and the flow rate of the supply water flowing through the water supply branch line; A hydrogen production system comprising:

5. The water vapor generating device includes a main heat exchanger that exchanges heat between at least a portion of the supply water and water vapor flowing through the water vapor discharge line, The hydrogen production system includes: a water supply line for supplying the supply water to the main heat exchanger; a water supply branch line communicating the water supply line with both the first heat exchanger and the second heat exchanger; a water vapor supply line communicating the main heat exchanger with the hydrogen electrode; a steam line communicating both the first heat exchanger and the second heat exchanger with the steam supply line; a first flow rate adjusting device that adjusts the flow rate of the supply water supplied to the main heat exchanger and the flow rate of the supply water flowing through the water supply branch line; The hydrogen production system according to claim 3 .

6. The method for operating a hydrogen production system according to claim 5 , further comprising the step of adjusting a flow rate of the supply water flowing through the branch water supply line by the first flow rate adjustment device.

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