Hydrogen production system

Abstract

Provided is a hydrogen production system (40) which comprises: an exhaust heat reception unit (41) that receives exhaust heat generated by an external exhaust heat source (11); a water vapor generation unit (42) that generates water vapor by heating water by means of the exhaust heat received by the exhaust heat reception unit (41); a cell stack (43) that electrolyzes the water vapor generated by the water vapor generation unit (42) so as to generate hydrogen; and a replenishment unit (44) that, when the amount of exhaust heat is insufficient with respect to the amount necessary for generating the required amount of water vapor, replenishes water, water vapor, or the water vapor generation unit (42) with heat, or replenishes the cell stack (43) with water vapor from an external water vapor supply source (95).

Description

Hydrogen Production System CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-134123, filed on August 9, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a hydrogen production system.

[0003] A conventional hydrogen production system described in Patent Document 1 is known, which generates hydrogen by generating steam from water using external waste heat and electrolyzing the generated steam using a cell stack. In this hydrogen production system, a methanation reaction section that generates methane is cooled with a fluid containing water. When the fluid vaporizes, the methanation reaction section is cooled by the heat of vaporization. Water vapor is generated by the vaporization of the water-containing fluid. Hydrogen is generated by electrolyzing the generated steam using the cell stack.

[0004] Japanese Patent Application Laid-Open No. 2024-12206

[0005] In the above configuration, if the reaction state in the methanation reaction unit fluctuates, there is a concern that the reaction heat in the methanation reaction unit may fluctuate. As a result, there is a concern that the amount or temperature of steam generated by cooling the methanation reaction unit may also fluctuate. As a result, there is a concern that it may be difficult to supply the cell stack with the amount or temperature of steam required for electrolysis.

[0006] The present disclosure seeks to provide a hydrogen production system in which the influence of fluctuations in external waste heat is reduced.

[0007] One aspect of the present disclosure is a hydrogen production system comprising: an exhaust heat receiving unit that receives exhaust heat generated from an external exhaust heat source; a steam generating unit that generates steam by heating water with the exhaust heat received by the exhaust heat receiving unit; a cell stack that generates hydrogen by electrolyzing the steam generated by the steam generating unit; and a replenishment unit that replenishes heat to the water, the steam, or the steam generating unit, or replenishes steam from an external steam source to the cell stack when the amount of exhaust heat is insufficient for generating the required amount of steam.

[0008] Fluctuations in the amount of waste heat generated from an external waste heat source may cause fluctuations in the amount or temperature of steam supplied to the cell stack. This may result in, for example, a decrease in the amount of steam generated in the steam generator or a drop in the temperature of the steam. In such cases, the amount or temperature of steam required for the cell stack to generate the required amount of hydrogen may be insufficient. According to one aspect of the present disclosure, when the temperature of the steam is insufficient, the temperature of the steam can be sufficiently increased by adding heat to the steam. Furthermore, when the amount of steam is insufficient, the amount of steam generated can be increased and the amount of steam can be compensated for by preheating water or by adding heat to the steam generator. The amount of steam can also be compensated for by adding water itself. As a result, even when the amount of waste heat generated from the external waste heat source fluctuates, fluctuations in the amount or temperature of steam supplied to the cell stack can be suppressed.

[0009] As described above, according to the above aspect, it is possible to provide a hydrogen production system in which the influence of fluctuations in external exhaust heat is reduced.

[0010] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 1 is a block diagram showing an ammonia synthesis apparatus and a hydrogen production system in Example 1, FIG. 2 is a block diagram showing a control device in Embodiment 1, FIG. 3 is a main flow showing the operation of the hydrogen production apparatus in Embodiment 1, FIG. 4 is a flowchart showing the processing when the exhaust heat temperature exceeds a first exhaust heat temperature threshold in Embodiment 1, FIG. 5 is a flowchart showing the processing when the exhaust heat temperature falls below a second exhaust heat temperature threshold in Embodiment 1, FIG. 6 is a flowchart showing the processing when an emergency stop of the cell stack occurs in Embodiment 1, FIG. 7 is a block diagram showing an ammonia synthesis apparatus and a hydrogen production system in Embodiment 2, FIG. 8 is a block diagram showing an ammonia synthesis apparatus and a hydrogen production system in Embodiment 3, FIG. 9 is a block diagram showing a control device in Embodiment 3, FIG. 10 is a block diagram showing an ammonia synthesis apparatus and a hydrogen production system in Embodiment 4, FIG. 11 is a partially enlarged block diagram showing an ammonia synthesis apparatus and a hydrogen production system in Embodiment 5, and FIG. 12 is a block diagram showing an ammonia synthesis apparatus and a hydrogen production system in Embodiment 6.

[0011] (Embodiment 1) An embodiment of a hydrogen production system 40 will be described with reference to FIGS. 1 and 2. The hydrogen production system 40 of this embodiment produces hydrogen by electrolyzing water vapor generated using waste heat from an external waste heat source. As shown in FIG. 1, the hydrogen production system 40 includes a waste heat receiving unit 41, a water vapor generating unit 42, a cell stack 43, and a replenishment unit 44. The waste heat receiving unit 41 receives waste heat from the external waste heat source. The water vapor generating unit 42 generates water vapor by heating water using the waste heat received by the waste heat receiving unit 41. The cell stack 43 electrolyzes the water vapor generated by the water vapor generating unit 42 to produce hydrogen. When the amount of waste heat is insufficient to generate the required amount of water vapor, the replenishment unit 44 replenishes heat to water, water vapor, or the water vapor generating unit 42, or replenishes water vapor from an external water vapor source to the cell stack 43.

[0012] As shown in FIG. 1 , the ammonia synthesis apparatus 10 a according to this embodiment includes an ammonia synthesizer 11, an exhaust heat line 12, a first heat exchanger 13, a first chiller 14, a second chiller 15, a refrigeration cycle unit 16, a storage unit 17, a first compressor 18, a produced hydrogen line 19, a nitrogen generator 20, a produced nitrogen line 21, a second compressor 22, a raw material gas supply line 23, a raw material gas heater 24, and a hydrogen production system 40.

[0013] The hydrogen production system 40 includes a water supply source 45, a water line 46, a first water pump 47, a second heat exchanger 48, a steam line 49, a first steam heater 50, a bypass line 51, a second water pump 52, a boiler 53, a bypass valve 54, a steam flow rate regulator 55, a second steam heater 56, a cell stack 43, a generated gas line 57, a radiator 58, a gas-liquid separator 59, a hydrogen line 60, a hydrogen flow rate regulator 61, an air line 62, a blower 63, an air heater 64, an emergency stop steam line 65, an emergency stop valve 66, an emergency stop radiator 67, an exhaust heat temperature sensor 69, a first steam temperature sensor 70, a second steam temperature sensor 71, a steam pressure sensor 72, and a control device 73.

[0014] The ammonia synthesis apparatus 10a is an example of an external exhaust heat source and an example of an apparatus for synthesizing hydrogen compounds. The external exhaust heat source is an apparatus external to the hydrogen production system 40. The external exhaust heat source is not particularly limited and may be, for example, an apparatus for synthesizing hydrogen compounds or a power plant. When an apparatus for synthesizing hydrogen compounds is used as the external exhaust heat source, the hydrogen compounds are not particularly limited and may be, for example, ammonia, methane, etc. In this case, the exhaust heat is not particularly limited and may be appropriately selected, for example, the reaction heat of hydrogen compounds or the heat of the outlet gas containing hydrogen compounds produced by the apparatus for synthesizing hydrogen compounds. Furthermore, when the exhaust heat source is a power plant, the power plant may be, for example, a geothermal power plant, a nuclear power plant, a thermal power plant, etc. When the external exhaust heat source is a power plant, the exhaust heat is not particularly limited and may be appropriately selected, for example, geothermal heat in the case of a geothermal power plant, the heat of the cooling medium of the nuclear reactor in the case of a nuclear power plant, or the heat of the turbine cooling water or the heat of the high-temperature gas after combustion in the case of a thermal power plant.

[0015] The ammonia synthesis apparatus 10a produces ammonia from a raw material gas containing hydrogen and nitrogen using a known chemical reaction. A raw material gas supply line 23 is connected to a portion of the ammonia synthesis apparatus 10a to which the raw material gas is supplied. The raw material gas containing hydrogen and nitrogen flows through the raw material gas supply line 23. A heat exhaust line 12 is connected to a portion of the ammonia synthesis apparatus 10a from which the product ammonia is discharged. A product gas containing ammonia produced by the ammonia synthesis apparatus 10a, unreacted hydrogen, unreacted nitrogen, etc. flows through the heat exhaust line 12. The exhaust heat generated when synthesizing ammonia in the ammonia synthesis apparatus 10a flows through the heat exhaust line 12 as thermal energy for the ammonia, etc. flowing through the heat exhaust line 12. The temperature of the product gas flowing out of the ammonia synthesis apparatus 10a is approximately 450°C. Note that, when temperatures are described in the following description, the temperature values ​​are merely examples and do not limit the embodiment.

[0016] A first heat exchanger 13, a second heat exchanger 48, a first chiller 14, a second chiller 15, a refrigeration cycle unit 16, and a storage unit 17 are arranged on the heat exhaust line 12. The first heat exchanger 13 is arranged at a position on the heat exhaust line 12 closest to the ammonia synthesis apparatus 10a. The first heat exchanger 13 is arranged across the heat exhaust line 12 and the raw material gas supply line 23. As a result, the first heat exchanger 13 receives the exhaust heat circulating through the heat exhaust line 12 and transfers the exhaust heat to the raw material gas circulating through the raw material gas supply line 23. As a result, the raw material gas circulating through the raw material gas supply line 23 is heated to approximately 200°C. The first heat exchanger 13 is an example of a raw material gas preheating unit.

[0017] The second heat exchanger 48 is disposed in the exhaust heat line 12 downstream of the first heat exchanger 13. The second heat exchanger 48 constitutes a part of the hydrogen production system 40. The second heat exchanger 48 receives heat from the exhaust heat in the exhaust heat line 12 and transfers the heat to water to generate steam. The temperature of the exhaust heat upstream of the second heat exchanger 48 is 300°C to 400°C, and the temperature of the exhaust heat downstream of the second heat exchanger 48 is approximately 100°C. The second heat exchanger 48 will be described in detail later.

[0018] A first chiller 14 is disposed on the exhaust heat line 12 downstream of the second heat exchanger 48. A refrigerant such as water flows through the first chiller 14. The refrigerant is not limited to water and can be selected appropriately taking cooling efficiency into consideration. The first chiller 14 cools the temperature of the generated gas from approximately 100°C to approximately 40°C.

[0019] A second chiller 15 is disposed on the exhaust heat line 12 downstream of the first chiller 14. A refrigerant such as water flows through the second chiller 15. The refrigerant is not limited to water and can be appropriately selected in consideration of cooling efficiency. The second chiller 15 cools the temperature of the generated gas from approximately 40°C to approximately 10°C.

[0020] A refrigeration cycle unit 16 is disposed on the heat exhaust line 12 downstream of the second chiller 15. The refrigeration cycle unit 16 includes an evaporator 16a disposed on the heat exhaust line 12, a refrigeration compressor 16b connected in parallel to the evaporator 16a, a condenser 16c, and an expansion valve 16d. The evaporator 16a, the refrigeration compressor 16b, the condenser 16c, and the expansion valve 16d are connected by a refrigerant line through which a known refrigerant flows. The refrigerant is compressed by the refrigeration compressor 16b, liquefied by the condenser 16c, and expanded by the expansion valve 16d. The refrigerant is then evaporated by the evaporator 16a, receiving heat from the product gas flowing through the heat exhaust line 12. This removes heat of vaporization from the product gas, cooling it. The product gas flowing through the heat exhaust line 12 is cooled by the refrigeration cycle unit 16 to a temperature of approximately 10°C to approximately 0°C.

[0021] The produced gas is cooled, and the ammonia is liquefied. However, the cooled produced gas may be compressed by a compressor (not shown) to liquefy the ammonia. As the ammonia is liquefied, the produced gas is separated into ammonia and unreacted hydrogen and nitrogen. The liquefied ammonia is stored in storage unit 17.

[0022] The portion of the exhaust heat line 12 between the refrigeration cycle unit 16 and the storage unit 17 is connected to the ammonia synthesizer 11 by the above-mentioned raw material gas supply line 23. The unreacted hydrogen and nitrogen separated from the product gas are supplied again to the ammonia synthesizer 11 via the raw material gas supply line 23.

[0023] A second compressor 22 is disposed on the raw material gas supply line 23. The raw material gas is heated to about 100°C by the second compressor 22.

[0024] The above-mentioned first heat exchanger 13 is disposed in the raw material gas supply line 23 downstream of the second compressor 22. The raw material gas at about 100°C is heated to about 200°C by this first heat exchanger 13.

[0025] A raw material gas heater 24 is disposed on the raw material gas supply line 23 upstream of the ammonia synthesizer 11. The raw material gas heater 24 further heats the raw material gas, which has been heated to approximately 200° C., to a higher temperature. The temperature after heating is optional and can be adjusted appropriately depending on the reaction conditions, etc.

[0026] A produced hydrogen line 19 is connected to the raw material gas supply line 23 at a position between the connection portion with the exhaust heat line 12 and the second compressor 22. Hydrogen produced by the hydrogen production system 40 flows through the produced hydrogen line 19.

[0027] A produced nitrogen line 21, which is connected to a nitrogen generator 20, is connected to the produced hydrogen line 19. Nitrogen is supplied from this produced nitrogen line 21 to the produced hydrogen line 19. As a result, hydrogen and nitrogen flow through the produced hydrogen line 19. The nitrogen generator 20 is not particularly limited, and a known configuration can be selected as appropriate.

[0028] A first compressor 18 is disposed in the product hydrogen line 19 between the connection portion with the product nitrogen line 21 and the connection portion with the raw material gas supply line 23. The first compressor 18 compresses the hydrogen and nitrogen flowing through the product hydrogen line 19.

[0029] Next, the hydrogen production system 40 will be described. The water supply source 45 in this embodiment is a tank that stores water. However, the water supply source 45 may also be a water production device that produces water. The water may also be pure water.

[0030] A water line 46 is connected to the water supply source 45. Water supplied from the water supply source 45 flows through the water line 46.

[0031] A first water pump 47 is connected downstream of the water line 46. The first water pump 47 supplies water to the second heat exchanger 48 at a predetermined flow rate.

[0032] The second heat exchanger 48 is disposed across the exhaust heat line 12 and the water line 46, and thermally connects the exhaust heat line 12 and the water line 46. In other words, the second heat exchanger 48 can transfer the exhaust heat flowing through the exhaust heat line 12 to the water flowing through the water line 46.

[0033] The portion of the second heat exchanger 48 that comes into contact with the exhaust heat line 12 and receives the exhaust heat from the exhaust heat line 12 is defined as an exhaust heat receiving section 41. The portion of the second heat exchanger 48 that comes into contact with the water line 46 is defined as a steam generating section 42 that generates steam by heating water with the exhaust heat received by the exhaust heat receiving section 41. Steam is generated from the water flowing through the water line 46 by the second heat exchanger 48.

[0034] The second heat exchanger 48 and the cell stack 43 are connected by a water vapor line 49. Water vapor generated by the water vapor generating unit 42 of the second heat exchanger 48 flows through the water vapor line 49. The water vapor is supplied to the cell stack 43 via the water vapor line 49.

[0035] A second steam heater 56 is disposed in the steam line 49 downstream of the second heat exchanger 48. The steam is heated by the second steam heater 56. The second steam heater 56 is an example of the replenishing unit 44 and an example of the heating unit 44a.

[0036] A water vapor flow rate regulator 55 is disposed in the water vapor line 49 downstream of the second water vapor heater 56. The water vapor flow rate regulator 55 regulates the flow rate of water vapor flowing through the water vapor line 49. The water vapor flow rate regulator 55 is not particularly limited, and any known means such as a variable valve or a mass flow controller can be appropriately selected.

[0037] A first steam heater 50 is disposed in the steam line 49 downstream of the steam flow rate regulator 55. The first steam heater 50 heats the steam flowing through the steam line 49. The first steam heater 50 is an example of the replenishing unit 44 and an example of the heating unit 44a.

[0038] The water vapor line 49 supplies water vapor to the cell stack 43. The cell stack 43 includes, for example, a solid oxide electrolysis cell (SOEC) having a cathode electrode and an anode electrode. The solid oxide electrolysis cell uses, for example, a solid oxide having oxygen ion conductivity. The electrolyte is not particularly limited, and any electrolyte such as a zirconia-based oxide can be appropriately selected.

[0039] The hydrogen production system 40 includes a hydrogen line 60 that is connected to a hydrogen supply source (not shown) and supplies hydrogen. A hydrogen flow rate regulator 61 is disposed in the hydrogen line 60. The hydrogen flow rate regulator 61 regulates the flow rate of hydrogen flowing through the hydrogen line 60. The hydrogen flow rate regulator 61 is not particularly limited, and any known means such as a variable valve or a mass flow controller can be appropriately selected.

[0040] The hydrogen line 60 is connected to a portion of the water vapor line 49 between the water vapor flow rate regulator 55 and the first water vapor heater 50 .

[0041] The hydrogen production system 40 includes an air line 62 that supplies air. A blower 63 is disposed in the air line 62. The blower 63 adjusts the flow rate of air flowing through the air line 62.

[0042] An air heater 64 is disposed in the air line 62 downstream of the blower 63. The air heater 64 heats the air flowing through the air line 62.

[0043] A product gas line 57 is connected to the cell stack 43. Hydrogen generated by the cell stack 43, unreacted water vapor, and the like flow through the product gas line 57. A radiator 58 is arranged downstream of the cell stack 43 on the product gas line 57. The radiator 58 lowers the temperature of the hydrogen and the like by radiating heat from the hydrogen and the like flowing through the product gas line 57 to the outside. The radiator 58 is not particularly limited, and any radiator 58 can be appropriately selected, for example, an air-cooled device, a water-cooled device using water as a refrigerant, a water-cooled refrigerator, an air-cooled refrigerator, or the like.

[0044] A gas-liquid separator 59 is disposed in the product gas line 57 downstream of the radiator 58. The gas-liquid separator 59 separates unreacted water vapor by condensing it into liquid water, thereby allowing hydrogen to flow through the product gas supply line.

[0045] An exhaust line 75 is also connected to the cell stack 43. Oxygen and air generated by the cell stack 43 flow through the exhaust line 75 as exhaust gas and are released to the outside.

[0046] Next, a description will be given of the bypass line 51. The bypass line 51 connects the upstream portion of the water line 46 from the first water pump 47 to the downstream portion of the steam line 49 from the second steam heater 56 to the steam flow rate regulator 55.

[0047] In the bypass line 51 , a second water pump 52 , a boiler 53 , and a bypass valve 54 are arranged in this order from the connection with the water line 46 toward the connection with the steam line 49 .

[0048] The second water pump 52 supplies the water flowing through the bypass line 51 to the boiler 53. The boiler 53 heats the water flowing through the bypass line 51 to generate steam. The boiler 53 is an example of the replenishment unit 44 and an example of the heating unit 44a. The bypass valve 54 adjusts the flow rate of the steam flowing through the bypass line 51. By adjusting the opening degree of the bypass valve 54, the bypass line 51 may be closed or the flow rate of the steam supplied from the bypass line 51 to the steam line 49 may be adjusted. However, the boiler 53 may be configured to be disposed between the first water pump 47 and the second heat exchanger 48.

[0049] Next, a description will be given of the emergency shutdown steam line 65. The emergency shutdown steam line 65 connects the water supply source 45 to a portion of the steam line 49 between the second steam heater 56 and the steam flow rate regulator 55.

[0050] The emergency stop steam line 65 is provided with an emergency stop valve 66 and an emergency stop radiator 67 in this order from the steam line 49 toward the water supply source 45 .

[0051] The emergency stop valve 66 is opened when the cell stack 43 is brought to an emergency stop. In other words, the emergency stop valve 66 is closed except when the cell stack 43 is brought to an emergency stop.

[0052] The emergency stop radiator 67 radiates heat from the steam flowing through the emergency stop steam line 65 to the receiving / removing section. This lowers the temperature of the steam flowing through the emergency stop steam line 65, generating liquid water. The generated water is supplied to the water supply source 45 and reused. However, the emergency stop steam line 65 may be configured not to be connected to the water supply source 45 but to be open to the outside. In this case, the liquid water generated by the emergency stop radiator 67 is discharged to the outside.

[0053] Next, the exhaust heat temperature sensor 69, the first water vapor temperature sensor 70, and the second water vapor temperature sensor 71 will be described.

[0054] The exhaust heat temperature sensor 69 is disposed in the exhaust heat line 12 between the first heat exchanger 13 and the second heat exchanger 48, in the vicinity of the second heat exchanger 48. The exhaust heat temperature sensor 69 acquires the temperature of the exhaust heat upstream of the second heat exchanger 48 and transmits it to the control device 73. The exhaust heat temperature sensor 69 is an example of an exhaust heat temperature acquisition unit. The exhaust heat temperature sensor 69 can be appropriately selected from temperature acquisition means such as a thermocouple or a thermistor. However, the exhaust heat temperature sensor 69 may also be configured to be disposed in a position in the exhaust heat line 12 between the ammonia synthesizer 11 and the first heat exchanger 13.

[0055] The first water vapor temperature sensor 70 is disposed in the water vapor line 49 between the second heater and the water vapor flow rate adjuster 55, near the water vapor flow rate adjuster 55. The first water vapor temperature sensor 70 acquires the temperature of the water vapor upstream of the water vapor flow rate adjuster 55 and transmits it to the control device 73. The first water vapor temperature sensor 70 is an example of a first water vapor temperature acquisition unit. The first water vapor temperature sensor 70 can be appropriately selected from temperature acquisition means such as a thermocouple or a thermistor.

[0056] The second steam temperature sensor 71 is disposed in the steam line 49 between the second heat exchanger 48 and the second heater, near the second heat exchanger 48. The second steam temperature sensor 71 acquires the temperature of the steam downstream of the second heat exchanger 48 and transmits it to the control device 73. The second steam temperature sensor 71 is an example of a second steam temperature acquisition unit. The second steam temperature sensor 71 can be appropriately selected from temperature acquisition means such as a thermocouple or a thermistor.

[0057] Next, the water vapor pressure sensor 72 will be described. The water vapor pressure sensor 72 is disposed in the bypass line 51 downstream of the bypass valve 54. The water vapor pressure sensor 72 acquires the pressure of the water vapor downstream of the bypass valve 54 and transmits it to the control device 73. The water vapor pressure sensor 72 is an example of a water vapor pressure acquisition unit. The water vapor pressure sensor 72 can be appropriately selected from a pressure gauge, a pressure sensor, etc.

[0058] Next, the control device 73 will be described with reference to Fig. 2. The control device 73 is configured with a well-known microcomputer having a processor, memory, etc., and its peripheral circuits. The control device 73 includes a refill control unit 73a, a first flow rate control unit 73b, a second flow rate control unit 73c, a third flow rate control unit 73d, a bypass valve control unit 73e, an emergency stop control unit 73f, and a memory unit 73g.

[0059] The storage unit 73g includes a known storage element such as a hard disk drive, a semiconductor storage element, etc. The storage unit 73g stores a first exhaust heat temperature threshold WT1, a second exhaust heat temperature threshold WT2, a first water vapor temperature threshold ST1, a second water vapor temperature threshold ST2, a water vapor temperature range TR, and a water vapor pressure range PR.

[0060] The first exhaust heat temperature threshold WT1 and the second exhaust heat temperature threshold WT2 are thresholds related to the temperature of the exhaust heat circulating through the exhaust heat line 12. In this embodiment, the first exhaust heat temperature threshold WT1 is greater than the second exhaust heat temperature threshold WT2. However, the first exhaust heat temperature threshold WT1 and the second exhaust heat temperature threshold WT2 may be the same value.

[0061] The first water vapor temperature threshold ST1 and the second water vapor temperature threshold ST2 are thresholds related to the temperature of water vapor in the water vapor line 49 upstream of the water vapor flow rate adjuster 55. However, the first water vapor temperature threshold ST1 and the second water vapor temperature threshold ST2 may be temperatures acquired by the second water vapor temperature sensor 71.

[0062] The water vapor temperature range TR is the temperature range of water vapor in the water vapor line 49 downstream of the water vapor generating unit 42. The water vapor pressure range PR is the pressure range of water vapor in the bypass line 51 downstream of the bypass valve 54.

[0063] The replenishment control unit 73a controls the operation of the second steam heater 56 based on the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69. Specifically, when the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69 falls below the second exhaust heat temperature threshold WT2 stored in the memory unit 73g, the replenishment control unit 73a turns on the second steam heater 56 to heat the steam flowing through the steam line 49.

[0064] The first flow rate control unit 73b controls the water vapor flow rate adjusting unit 55 based on the temperature of the water vapor acquired by the first water vapor temperature sensor 70 to adjust the flow rate of the water vapor.

[0065] For example, when the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69 falls below the second exhaust heat temperature threshold WT2 and the temperature of the water vapor acquired by the first water vapor temperature sensor 70 falls below the second water vapor temperature threshold ST2, the first flow rate control unit 73b may be configured to reduce the flow rate of water vapor by controlling the water vapor flow rate adjustment unit 55 based on the temperature of the water vapor acquired by the first water vapor temperature sensor 70.

[0066] Furthermore, for example, when the temperature of the exhaust heat acquired from the acquisition unit by the exhaust heat temperature sensor 69 exceeds the first exhaust heat temperature threshold WT1 and the temperature of the water vapor acquired by the first water vapor temperature sensor 70 exceeds the first water vapor temperature threshold ST1, the first flow rate control unit 73b may be configured to increase the flow rate of water vapor by controlling the water vapor flow rate adjustment unit 55 based on the temperature of the water vapor acquired by the first water vapor temperature sensor 70.

[0067] The second flow rate control unit 73 c controls the discharge rate of the first water pump 47 based on the temperature of the water vapor acquired by the second water vapor temperature sensor 71 .

[0068] For example, the second flow control unit 73c may be configured to reduce the discharge volume of the first water pump 47 when the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69 falls below the second exhaust heat temperature threshold WT2 so that the temperature of the water vapor acquired by the second water vapor temperature sensor 71 falls within the water vapor temperature range TR.

[0069] Furthermore, for example, the second flow control unit 73c may be configured to increase the discharge volume of the first water pump 47 so that the temperature of the water vapor acquired by the second water vapor temperature sensor 71 falls within the water vapor temperature range TR when the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69 exceeds the first exhaust heat temperature threshold WT1.

[0070] When the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69 falls below the second exhaust heat temperature threshold WT2, the bypass valve control unit 73e adjusts the aperture of the bypass valve 54 so that the pressure of the water vapor acquired by the water vapor pressure sensor 72 falls within the water vapor pressure range PR. Furthermore, when the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69 exceeds the first exhaust heat temperature threshold WT1, the bypass valve control unit 73e adjusts the aperture of the bypass valve 54 so that the pressure of the water vapor acquired by the water vapor pressure sensor 72 falls within the water vapor pressure range PR.

[0071] When the cell stack 43 comes to an emergency stop, the emergency stop control unit 73 f opens the emergency stop valve 66 and controls the water vapor flow rate adjustment unit 55 to stop the supply of water vapor to the cell stack 43 .

[0072] Next, the operation of the hydrogen production system 40 according to this embodiment will be described with reference to Figures 3 to 6. Figure 3 shows a main flow of the hydrogen production system 40 according to this embodiment.

[0073] As shown in Fig. 3, when the hydrogen production system 40 is started, the exhaust heat temperature sensor 69 acquires the temperature of the exhaust heat and transmits it to the first flow rate control unit 73b of the control device 73. The first flow rate control unit 73b determines whether the temperature of the exhaust heat exceeds the first exhaust heat temperature threshold WT1 stored in the memory unit 73g (S1). If the temperature of the exhaust heat exceeds the first exhaust heat temperature threshold WT1 (S1: Y), the first flow rate control unit 73b determines whether the temperature of the water vapor acquired by the first water vapor temperature sensor 70 has increased (S10), as shown in Fig. 4. If the temperature of the water vapor acquired by the first water vapor temperature sensor 70 has not increased (S10: N), the process returns to Fig. 3 and S1 is executed.

[0074] Returning to Figure 4, if the temperature of the water vapor acquired by the first water vapor temperature sensor 70 exceeds the first water vapor temperature threshold ST1 (S10: Y), the first flow rate control unit 73b controls the water vapor flow rate adjustment unit 55 to increase the mass flow rate of water vapor flowing through the water vapor line 49 (S11).

[0075] Next, the second flow rate control unit 73c determines whether the water vapor temperature acquired by the second water vapor temperature sensor 71 is within the water vapor temperature range TR (S12). If the water vapor temperature acquired by the second water vapor temperature sensor 71 is within the water vapor temperature range TR (S12: Y), the process returns to S10.

[0076] If the water vapor temperature acquired by the second water vapor temperature sensor 71 is not within the water vapor temperature range TR (S12: N), the second flow control unit 73c controls the first water pump 47 to adjust the amount of water supplied to the second heat exchanger 48 so that the water vapor temperature acquired by the second water vapor temperature sensor 71 is within the water vapor temperature range TR (S13).

[0077] Next, the bypass valve control unit 73e determines whether the pressure of the water vapor acquired by the water vapor pressure sensor 72 is within the water vapor pressure range PR (S14). If the pressure of the water vapor acquired by the water vapor pressure sensor 72 is within the water vapor pressure range PR (S14: Y), the process returns to S10.

[0078] If the water vapor pressure acquired by the water vapor pressure sensor 72 is not within the water vapor pressure range PR (S14: N), the bypass valve control unit 73e adjusts the opening of the bypass valve 54 so that the water vapor pressure acquired by the water vapor pressure sensor 72 is within the water vapor pressure range PR (S15). After S15 is executed, the process returns to S10. However, the water vapor pressure sensor 72 and the bypass valve 54 may be omitted. If the water vapor pressure sensor 72 and the bypass valve 54 are omitted, S14 and S15 are omitted from the flowchart of FIG. 4.

[0079] 3, if the temperature of the exhaust heat is not higher than the first exhaust heat temperature threshold WT1 (S1: N), the replenishment control unit 73a determines whether the temperature of the exhaust heat is lower than the second exhaust heat temperature threshold WT2 (S2). If the temperature of the exhaust heat is lower than the second exhaust heat temperature threshold WT2 (S2: Y), the replenishment control unit 73a turns on the second steam heater 56 (S21), as shown in FIG.

[0080] Next, the first flow rate control unit 73b determines whether the temperature of the water vapor acquired by the first water vapor temperature sensor 70 is below the second water vapor temperature threshold ST2 (S22). If the temperature of the water vapor acquired by the first water vapor temperature sensor 70 is not below the second water vapor temperature threshold ST2 (S22: N), the process returns to FIG. 3 and S1 is executed.

[0081] Returning to Figure 5, if the temperature of the water vapor acquired by the first water vapor temperature sensor 70 falls below the second water vapor temperature threshold ST2 (S22: Y), the first flow rate control unit 73b controls the water vapor flow rate adjustment unit 55 to reduce the mass flow rate of water vapor flowing through the water vapor line 49 (S23).

[0082] Next, the second flow rate control unit 73c determines whether the water vapor temperature acquired by the second water vapor temperature sensor 71 is within the water vapor temperature range TR (S24). If the water vapor temperature acquired by the second water vapor temperature sensor 71 is within the water vapor temperature range TR (S24: Y), the process returns to S22.

[0083] If the water vapor temperature acquired by the second water vapor temperature sensor 71 is not within the water vapor temperature range TR (S22: N), the second flow control unit 73c controls the first water pump 47 to adjust the amount of water supplied to the second heat exchanger 48 so that the water vapor temperature acquired by the second water vapor temperature sensor 71 is within the water vapor temperature range TR (S25).

[0084] Next, the bypass valve control unit 73e determines whether the pressure of the water vapor acquired by the water vapor pressure sensor 72 is within the water vapor pressure range PR (S26). If the pressure of the water vapor acquired by the water vapor pressure sensor 72 is within the water vapor pressure range PR (S26: Y), the process returns to S22.

[0085] If the water vapor pressure acquired by the water vapor pressure sensor 72 is not within the water vapor pressure range PR (S26: N), the bypass valve control unit 73e adjusts the opening of the bypass valve 54 so that the water vapor pressure acquired by the water vapor pressure sensor 72 is within the water vapor pressure range PR (S27). After S27 is executed, the process returns to S22. However, as described above, the water vapor pressure sensor 72 and the bypass valve 54 may be omitted. If the water vapor pressure sensor 72 and the bypass valve 54 are omitted, S26 and S27 are omitted from the flowchart of FIG. 5.

[0086] 3, the emergency stop control unit 73f determines whether the cell stack 43 has been brought to an emergency stop (S3). If the cell stack 43 has been brought to an emergency stop (S3: Y), the emergency stop control unit 73f stops the boiler 53 (S31), as shown in FIG. 6. This stops the generation of steam in the bypass line 51.

[0087] Next, the emergency stop control unit 73f opens the emergency stop valve 66 (S32), which allows steam to flow through the emergency stop steam line 65.

[0088] Next, the emergency stop control unit 73f controls the water vapor flow rate adjusting unit 55 to stop the supply of water vapor to the cell stack 43 (S33).

[0089] As a result, the water vapor flowing through the emergency stop water vapor line 65 is cooled in the emergency stop radiator 67 and condenses into liquid water. The condensed water moves to the water supply source 45 to which the emergency stop water vapor line 65 is connected and is reused.

[0090] After S33 is executed, the process returns to FIG. 3 and the operation of the hydrogen production system 40 ends.

[0091] If the cell stack 43 has not been brought to an emergency stop (S3: N), the control device 73 determines whether or not an instruction to stop the hydrogen production system 40 has been issued (S4). If an instruction to stop the hydrogen production system 40 has not been issued (S4: N), the process returns to S1.

[0092] If an instruction to stop the hydrogen production system 40 has been issued (S4: Y), the control device 73 stops the hydrogen production system 40. With the above, the operation of the hydrogen production system 40 ends.

[0093] Next, the effects of this embodiment will be described. The hydrogen production system 40 according to this embodiment includes an exhaust heat receiving unit 41, a steam generating unit 42, a cell stack 43, a boiler 53, a first steam heater 50, and a second steam heater 56. The exhaust heat receiving unit 41 receives exhaust heat discharged from the ammonia synthesizer 11. The steam generating unit 42 generates steam by heating water with the exhaust heat received by the exhaust heat receiving unit 41. The boiler 53 supplements heat to the water when the amount of exhaust heat is insufficient for generating the required amount of steam. The first steam heater 50 and the second steam heater 56 supplement heat to the steam when the amount of exhaust heat is insufficient.

[0094] Fluctuations in the amount of exhaust heat generated by the ammonia synthesizer 11 may cause fluctuations in the amount or temperature of steam supplied to the cell stack 43. Furthermore, fluctuations in the amount of hydrogen produced by the cell stack 43 may also cause fluctuations in the amount of steam required, potentially resulting in a difference between the amount of exhaust heat and the amount of heat required to produce the required amount of steam. This raises concerns, for example, that the amount of steam generated by the steam generator 42 may decrease, or the temperature of the steam may drop. In such cases, the amount or temperature of steam required for the cell stack 43 to produce hydrogen may be insufficient. According to this embodiment, when the temperature of the steam is insufficient, heat can be added to the steam to sufficiently increase the temperature of the steam. Furthermore, when the amount of steam is insufficient, heat can be added to the water to increase the amount of steam produced and compensate for the lack of steam. As a result, even when the amount of exhaust heat generated by the ammonia synthesizer 11 fluctuates, fluctuations in the amount or temperature of steam supplied to the cell stack 43 can be suppressed. The required amount of water vapor is the amount of water vapor required to generate the amount of hydrogen generated by the cell stack 43. When the amount of hydrogen generated by the cell stack 43 is constant, the amount of water vapor required is also constant. However, when the amount of hydrogen generated by the cell stack 43 fluctuates, the amount of water vapor required may also fluctuate.

[0095] The steam production system according to this embodiment is provided with at least two heating units 44a, including a boiler 53, a first steam heater 50, and a second steam heater 56. This allows the cell stack 43 to stably supply the steam required to generate hydrogen, even if the amount of exhaust heat generated from the ammonia synthesizer 11 fluctuates.

[0096] The hydrogen production system 40 according to this embodiment further includes a steam line 49 through which steam flows, connecting the steam generator 42 and the cell stack 43. The steam production system includes a first steam heater 50 arranged in the steam line 49 upstream of the cell stack 43 and heating the steam immediately before it is supplied to the cell stack 43.

[0097] According to this embodiment, the steam can be heated just before it is supplied to the cell stack 43, so that even if the exhaust heat fluctuates, fluctuations in the temperature of the steam supplied to the cell stack 43 can be suppressed.

[0098] The hydrogen production system 40 according to this embodiment further includes a waste heat temperature sensor 69, a replenishment control unit 73a, and a steam line 49. The waste heat temperature sensor 69 acquires the temperature of the waste heat. The replenishment control unit 73a controls the operation of the boiler 53, the first steam heater 50, and the second steam heater 56 based on the temperature of the waste heat. The hydrogen production system 40 also includes a second steam heater 56 that is disposed downstream of the steam generator 42 in the steam line 49 and heats the steam immediately after it is generated by the steam generator 42. The replenishment control unit 73a turns on the second steam heater 56 when the temperature of the waste heat acquired by the waste heat temperature sensor 69 falls below a second waste heat temperature threshold WT2.

[0099] According to this embodiment, when the exhaust heat from the ammonia synthesizer 11 decreases and the temperature of the exhaust heat falls below the second exhaust heat temperature threshold WT2, the temperature of the water vapor can be sufficiently increased by turning on the second water vapor heater 56. This makes it possible to prevent water vapor near the dew point from condensing into water droplets while the water vapor is moving from the water vapor generator 42 to the cell stack 43.

[0100] The hydrogen production system 40 according to this embodiment further includes a water vapor flow rate regulator 55 and a first flow rate controller 73b. The water vapor flow rate regulator 55 is disposed in the water vapor line 49 between the second water vapor heater 56 and the cell stack 43 to regulate the flow rate of water vapor. When the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69 falls below the second exhaust heat temperature threshold value WT2, the water vapor flow rate regulator 55 controls the water vapor flow rate regulator 55 to reduce the flow rate of water vapor.

[0101] When the temperature of water vapor upstream of the water vapor flow rate adjuster 55 exceeds the first exhaust heat temperature threshold WT1, the mass flow rate increases. In this embodiment, when the temperature of water vapor upstream of the water vapor flow rate adjuster 55 exceeds the first exhaust heat temperature threshold WT1, the water vapor flow rate adjuster 55 is controlled to reduce the flow rate of water vapor. This makes it possible to suppress changes in the mass flow rate of water vapor supplied to the cell stack 43.

[0102] The hydrogen production system 40 according to this embodiment further includes a water line 46, a first water pump 47, a second steam temperature sensor 71, and a second flow rate control unit 73c. ​​The water line 46 connects the water supply source 45 and the steam generator 42. The first water pump 47 is disposed on the water line 46 and supplies water to the steam generator 42. The second steam temperature sensor 71 is disposed on the steam line 49 and acquires the temperature of the steam downstream of the steam generator 42. The second flow rate control unit 73c adjusts the discharge rate of the first water pump 47 based on the temperature of the exhaust heat acquired by the exhaust heat temperature sensor 69 so that the temperature of the steam acquired by the second steam temperature sensor 71 falls within the steam temperature range TR.

[0103] If the temperature of the exhaust heat obtained from the exhaust heat temperature sensor 69 falls below the second exhaust heat temperature threshold WT2, the amount of exhaust heat may be insufficient. Therefore, by adjusting the discharge rate of the first water pump 47 and the amount of water supplied to the steam generator 42 so that the temperature of the water vapor downstream of the steam generator 42 falls within the steam temperature range TR, this insufficient amount of exhaust heat can be prevented. On the other hand, if the temperature of the exhaust heat obtained from the exhaust heat temperature sensor 69 exceeds the first exhaust heat temperature threshold WT1, the amount of exhaust heat may be excessive. Therefore, by adjusting the discharge rate of the first water pump 47 and the amount of water supplied to the steam generator 42 so that the temperature of the water vapor downstream of the steam generator 42 falls within the steam temperature range TR, this excessive amount of exhaust heat can be prevented.

[0104] The hydrogen production system 40 according to this embodiment further includes a bypass line 51, a boiler 53, a bypass valve 54, a steam pressure sensor 72, and a bypass valve control unit 73e. The bypass line 51 connects the water line 46 upstream of the first water pump 47 to the steam line 49 between the steam generator 42 and the steam flow rate regulator 55. The boiler 53 is disposed in the bypass line 51 and heats water to generate steam. The bypass valve 54 is disposed in the bypass line 51 downstream of the boiler 53 and adjusts the flow rate of the steam. The steam pressure sensor 72 detects the pressure of the steam flowing through the bypass line 51 downstream of the bypass valve 54. The bypass valve control unit 73e adjusts the aperture of the bypass valve 54 when the temperature of the exhaust heat detected by the exhaust heat temperature sensor 69 falls below the second exhaust heat temperature threshold WT2 and the pressure of the steam detected by the steam pressure sensor 72 is within the steam pressure range.

[0105] If the temperature of the exhaust heat acquired from the exhaust heat temperature sensor 69 falls below the second exhaust heat temperature threshold WT2, there is a risk of an insufficient amount of exhaust heat. In this case, there is a concern that the amount of steam generated by the steam generator 42 will be insufficient. Therefore, by adjusting the aperture of the bypass valve 54 so that the pressure of the steam generated by the boiler 53 arranged in the bypass line 51 falls within a predetermined steam pressure range, it is possible to prevent an insufficiency in the amount of steam circulating through the steam line 49.

[0106] The hydrogen production system 40 according to this embodiment further includes an emergency stop steam line 65, an emergency stop valve 66, an emergency stop chiller 68, and an emergency stop control unit 73f. The emergency stop steam line 65 connects the upstream portion of the steam flow rate regulator 55 of the steam line 49 to the water supply source 45. The emergency stop valve 66 is disposed on the emergency stop steam line 65. The emergency stop chiller 68 cools the steam disposed on the emergency stop steam line 65 to produce water. When the cell stack 43 undergoes an emergency stop, the emergency stop control unit 73f opens the emergency stop valve 66 and controls the steam flow rate regulator 55 to stop the supply of steam to the cell stack 43, and turns on the emergency stop chiller 68 to produce water from the steam.

[0107] According to this embodiment, in the event of an emergency shutdown of the cell stack 43, water can be produced from the steam flowing through the steam line 49 and returned to the water supply source 45. This prevents the second heat exchanger 48 from receiving the exhaust heat and high-temperature heat being supplied downstream of the exhaust heat source, thereby preventing malfunction of the ammonia synthesis apparatus 10a. Furthermore, it is possible to prevent the wasteful disposal of steam during an emergency shutdown.

[0108] Furthermore, the external exhaust heat source according to this embodiment is the ammonia synthesizer 11, and the exhaust heat is the reaction heat generated when ammonia is synthesized in the ammonia synthesizer 11 and the heat quantity of the product gas discharged from the ammonia synthesizer 11. According to this embodiment, the exhaust heat discharged from the ammonia synthesizer 11 is used to generate steam, and this steam is electrolyzed in the cell stack 43 to generate hydrogen, so that the exhaust heat can be effectively utilized.

[0109] The external exhaust heat source according to this embodiment is an ammonia synthesizer 11 that synthesizes ammonia, which is a hydrogen compound. An exhaust heat line 12, through which exhaust heat is transferred, is connected to the ammonia synthesizer 11. A first heat exchanger 13 that supplies exhaust heat to hydrogen and nitrogen, which are raw material gases supplied to the ammonia synthesizer 11, is disposed in the exhaust heat line 12.

[0110] According to this embodiment, the exhaust heat can be used to preheat the raw material gas supplied to the ammonia synthesizer 11, and therefore the exhaust heat can be used effectively.

[0111] The hydrogen production system 40 according to this embodiment further includes an exhaust heat temperature sensor 69 disposed in the exhaust heat line 12 between the ammonia synthesizer 11 and the first heat exchanger 13 to acquire the temperature of the exhaust heat, and a control device 73 that controls the operation of the boiler 53, the second steam heater 56, and the first steam heater 50 based on the temperature of the exhaust heat. According to this embodiment, the exhaust heat temperature can be measured further upstream in the exhaust heat line 12. This allows the temperature of the exhaust heat sent to the first heat exchanger 13 to be acquired earlier. As a result, the boiler 53, the second steam heater 56, and the first steam heater 50 can be controlled earlier, further reducing the effects of fluctuations in the temperature and flow rate of the exhaust heat.

[0112] (Embodiment 2) Next, embodiment 2 will be described with reference to Fig. 7. Note that, among the symbols used in embodiment 2 and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0113] As shown in FIG. 7, an ammonia synthesis apparatus 10b according to this embodiment differs from the first embodiment in that it does not include a first chiller 14.

[0114] The ammonia synthesis apparatus 10b also includes a heat transfer line 80, a third heat exchanger 81, a heat medium pump 82, a heat pump 83, and a fourth heat exchanger 84. The heat pump 83 includes a refrigerant line 85, a compressor 86, and an expansion valve 87. The second embodiment differs from the first embodiment in these configurations.

[0115] However, the heat transfer line 80, the third heat exchanger 81, and the heat medium pump 82 may be omitted, and the second heat exchanger 48 and the fourth heat exchanger 84 may be connected by the heat pump 83.

[0116] Furthermore, the water line 46 connected to the water supply source 45 in this embodiment is connected to a fourth heat exchanger 84. The fourth heat exchanger 84 is an example of the replenishing unit 44 and an example of the heating unit 44a. The fourth heat exchanger 84 is also an example of the steam generating unit 42 that generates steam from the water supplied from the water line 46. In this respect, the second embodiment differs from the first embodiment.

[0117] The water vapor line 49 according to this embodiment connects the fourth heat exchanger 84 and the water vapor flow rate regulator 55. The water vapor line 49 passes through the water vapor generated in the fourth heat exchanger 84.

[0118] An emergency stop steam line 65 is connected to the steam line 49 at a position upstream of the steam flow rate regulator 55 .

[0119] The heat transfer line 80 is formed in a loop shape and thermally connects the second heat exchanger 48 and the third heat exchanger 81. A heat medium flows through the heat transfer line 80. The heat medium is suitably selected from non-volatile liquids such as mineral oil and non-volatile organic compounds. In this embodiment, the temperature of the heat medium is set to less than 100°C.

[0120] The third heat exchanger 81 transfers the heat received from the heat medium to the heat pump 83 .

[0121] A heat medium pump 82 is disposed downstream of the third heat exchanger 81 and upstream of the second heat exchanger 48 in the flow direction of the heat medium in the heat transfer line 80. The flow rate of the heat medium supplied to the second heat exchanger 48 can be adjusted by discharging the heat medium from the heat medium pump 82.

[0122] The heat pump 83 includes a refrigerant line 85 formed in a loop. A refrigerant flows through the refrigerant line 85. The refrigerant may be, for example, a chlorofluorocarbon gas, or a non-chlorofluorocarbon gas such as carbon dioxide gas, ammonia, or propane gas. Alternatively, the refrigerant may be an aqueous solution of lithium bromide or the like. The heat pump 83 is an example of the refill unit 44 and an example of the heating unit 44a.

[0123] The compressor 86 is disposed in the refrigerant line 85 and compresses the refrigerant to liquefy it. The temperature of the refrigerant increases as a result of being compressed.

[0124] The fourth heat exchanger 84 receives heat from the liquefied refrigerant and transfers the heat to the water flowing through the water line 46, thereby generating water vapor. The temperature of the refrigerant decreases as it transfers heat to the water.

[0125] The expansion valve 87 is disposed in the refrigerant line 85. The expansion valve 87 expands the refrigerant to vaporize it. The temperature of the refrigerant decreases as the refrigerant vaporizes.

[0126] In the third heat exchanger 81, the refrigerant receives heat from the heat medium and its temperature increases.

[0127] A refrigerant temperature sensor 88 that acquires the temperature of the refrigerant is disposed in the refrigerant line 85 between the compressor 86 and the fourth heat exchanger 84. The refrigerant temperature sensor 88 transmits the temperature acquired from the refrigerant to the control device 73. The control device 73 controls the operation of the compressor 86 based on the refrigerant temperature acquired from the refrigerant temperature sensor 88.

[0128] According to this embodiment, by operating the heat pump 83, it is possible to increase the temperature of the refrigerant flowing through the refrigerant line 85. As a result, heat can be replenished to the water in the fourth heat exchanger 84 connected to the heat pump 83.

[0129] Furthermore, according to this embodiment, fluctuations in the temperature of the heat medium in the lower stage of the second heat exchanger 48 in the heat transfer line 80 are smaller than fluctuations in the exhaust heat temperature acquired by the exhaust heat temperature acquisition unit 69, and furthermore, fluctuations in the temperature of the refrigerant line 85 acquired by the refrigerant temperature sensor 88 are also smaller, so that even if the amount of exhaust heat generated from the ammonia synthesizer 11 fluctuates, fluctuations in the amount or temperature of the water vapor supplied to the cell stack 43 can be suppressed. Note that in this embodiment, the second heat exchanger 48 is the exhaust heat receiving unit 41.

[0130] In this embodiment, the exhaust heat is recovered using a relatively low-temperature heat medium. This allows the exhaust heat to be recovered efficiently even at lower temperatures. As a result, the efficiency of the cell stack 43 can be improved. Furthermore, since the temperature of the exhaust heat downstream of the second heat exchanger 48 can be lowered to approximately 40°C, the first chiller 14 can be omitted. The capacity of the second chiller 15 can also be reduced.

[0131] (Embodiment 3) Next, embodiment 3 will be described with reference to Figures 8 and 9. As shown in Figure 8, an ammonia synthesis apparatus 10c according to this embodiment includes a fifth heat exchanger 90, a sixth heat exchanger 91, a heat transfer line 80, a heat medium heater 92, a heat medium pump 82, and a heat medium temperature sensor 93. In these respects, embodiment 3 differs from embodiment 1.

[0132] A fifth heat exchanger 90 is disposed in the exhaust heat line 12 downstream of the second heat exchanger 48. A water line 46 is connected to the fifth heat exchanger 90, thereby supplying water to the fifth heat exchanger 90. The fifth heat exchanger 90 is an example of the replenishment unit 44, an example of the heating unit 44a, and an example of the water preheating unit 44b. Water is preheated in the fifth heat exchanger 90. After receiving heat in the fifth heat exchanger 90, a portion of the water may undergo a phase change to steam, resulting in a state in which gaseous steam and liquid steam coexist, or the water may be entirely liquid water. In this embodiment, the second heat exchanger 48 is the exhaust heat receiving unit 41. The fifth heat exchanger 90 may be applied to the first or second embodiment.

[0133] The heat transfer line 80 is connected to the second heat exchanger 48 and receives the exhaust heat from the exhaust heat line 12. A heat medium flows through the heat transfer line 80. A heat medium heater 92 is disposed in the heat transfer line 80 downstream of the second heat exchanger 48. The heat medium heater 92 heats the heat medium flowing through the heat transfer line 80. The heat medium heater 92 is an example of the refill unit 44 and an example of the heating unit 44a.

[0134] A heat medium temperature sensor 93 that acquires the temperature of the heat medium is disposed in the heat transfer line 80 downstream of the heat medium heater 92. The heat medium temperature sensor 93 transmits the acquired heat medium temperature to the control device 73. The heat medium temperature sensor 93 is an example of a heat medium temperature acquisition unit.

[0135] 9, the control device 73 includes a replenishment control unit 73a, an emergency stop control unit 73f, and a memory unit 73g. A heat medium temperature threshold MT is stored in the memory unit 73g of the control device 73. When the temperature of the heat medium acquired by the heat medium temperature sensor 93 falls below the heat medium temperature threshold MT, the replenishment control unit 73a turns on the heat medium heater 92. This heats the heat medium.

[0136] The fifth heat exchanger 90 and the sixth heat exchanger 91 are connected by a water line 46. Liquid water flows through the water line 46 between the fifth heat exchanger 90 and the sixth heat exchanger 91. However, some of the water may be vaporized into water vapor.

[0137] The sixth heat exchanger 91 receives heat from the heat medium flowing through the heat transfer line 80 and transfers the heat to the water flowing through the water line 46 to heat the water and generate steam. The sixth heat exchanger 91 is an example of the steam generating unit 42.

[0138] According to this embodiment, the heat medium heater 92 heats the heat medium to supplement heat to the sixth heat exchanger 91. This increases the amount of water vapor produced, making it possible to compensate for the amount of water vapor. As a result, even if the amount of exhaust heat generated from the ammonia synthesizer 11 fluctuates, fluctuations in the amount or temperature of water vapor supplied to the cell stack 43 can be suppressed.

[0139] Furthermore, according to this embodiment, the fifth heat exchanger 90 preheats the water by transferring heat to the water. This allows the waste heat to be recovered without waste, even at lower temperatures. As a result, the efficiency of the cell stack 43 can be improved. Furthermore, since the temperature of the waste heat downstream of the fifth heat exchanger 90 can be lowered to approximately 40°C, the first chiller 14 can be omitted. Furthermore, the capacity of the second chiller 15 can also be reduced.

[0140] The hydrogen production system 40 according to this embodiment includes a heat transfer line 80 connecting the second heat exchanger 48 and the sixth heat exchanger 91, a heat medium that flows through the heat transfer line 80 to transfer heat from the second heat exchanger 48 to the sixth heat exchanger 91, a heat medium temperature sensor 93 that acquires the temperature of the heat medium flowing through the heat transfer line 80, and a replenishment control unit 73a that controls the operation of the replenishment unit 44 based on the temperature of the heat medium. The replenishment unit 44 is a heat medium heater 92 that is disposed in the heat transfer line 80 and heats the heat medium. The replenishment control unit 73a turns on the heat medium heater 92 when the temperature of the heat medium acquired from the heat medium temperature sensor 93 falls below a heat medium temperature threshold MT.

[0141] According to this embodiment, by using a heat medium with a relatively large heat capacity, it is possible to improve robustness against temperature fluctuations of the exhaust heat, thereby enabling the cell stack 43 to stably supply the water vapor required to generate hydrogen even if the amount of exhaust heat generated from the ammonia synthesizer 11 fluctuates.

[0142] Furthermore, according to this embodiment, the exhaust heat is received by the heat medium flowing through the heat transfer line 80, so that the influence of fluctuations in the exhaust heat can be alleviated.

[0143] Furthermore, according to this embodiment, the ammonia synthesizer 11 is connected to the exhaust heat line 12 through which exhaust heat is transferred, and the fifth heat exchanger 90 is disposed on the exhaust heat line 12 downstream of the second heat exchanger 48, and receives the exhaust heat to preheat the water before it is circulated to the sixth heat exchanger 91.

[0144] According to this embodiment, the waste heat that was not fully received by the second heat exchanger 48 can be received by the fifth heat exchanger 90 to preheat the water. This allows the waste heat to be recovered without waste, even at lower temperatures. As a result, the efficiency of the cell stack 43 can be improved. In addition, the capacity of the second chiller 15 can also be reduced.

[0145] Fourth Embodiment Next, a fourth embodiment will be described with reference to Fig. 10. An ammonia synthesis apparatus 10d according to the fourth embodiment differs from the third embodiment in that it includes a seventh heat exchanger 94 instead of the radiator 58.

[0146] Furthermore, this embodiment differs from the third embodiment in that the water line 46 connects the water supply source 45 , the fifth heat exchanger 90 , the seventh heat exchanger 94 , and the sixth heat exchanger 91 .

[0147] In this embodiment, the water that has received heat from the exhaust heat in the fifth heat exchanger 90 flows through the water line 46 and moves to the seventh heat exchanger 94 .

[0148] The seventh heat exchanger 94 is disposed in the product gas line 57 connected to the cell stack 43, upstream of the gas-liquid separator 59. The temperature of the hydrogen produced in the cell stack 43 is 150°C or higher. The seventh heat exchanger 94 transfers heat received from the hydrogen to water to preheat the water. The water may be heated in a liquid state, or a portion of the water may undergo a phase change to steam. The seventh heat exchanger 94 is an example of the replenishment unit 44, an example of the heating unit 44a, and an example of the water preheating unit 44b.

[0149] The water preheated in the seventh heat exchanger 94 flows through the water line 46 and moves to the sixth heat exchanger 91. The sixth heat exchanger 91 receives heat from the heat medium and transfers the heat to the water to generate steam from the water.

[0150] According to this embodiment, the ammonia synthesizer 11 is connected to the exhaust heat line 12 through which exhaust heat is transferred, and the fifth heat exchanger 90 is disposed on the exhaust heat line 12 downstream of the second heat exchanger 48, and receives the exhaust heat to preheat the water before it is circulated to the sixth heat exchanger 91. This makes it possible to effectively utilize the exhaust heat that was not fully recovered, thereby improving the overall energy efficiency of the hydrogen production system 40. Furthermore, it is possible to reduce the energy required for cooling, and thus improve the energy efficiency of the ammonia synthesizer 10d.

[0151] Furthermore, since the heat of the hydrogen produced by the cell stack 43 can be effectively utilized, the energy efficiency of the hydrogen production system 40 can be improved overall.

[0152] (Embodiment 5) Next, embodiment 5 will be described with reference to Fig. 11 . An ammonia synthesis apparatus 10e and a hydrogen production system 40 according to this embodiment differ from embodiment 4 in that an eighth heat exchanger 94a is provided. The eighth heat exchanger 94a is disposed in the exhaust line 75. The eighth heat exchanger 94a is also connected to the seventh heat exchanger 94 by the water line 46. As a result, the water preheated by the seventh heat exchanger 94 is further preheated by the eighth heat exchanger 94a. In this embodiment, the seventh heat exchanger 94 and the eighth heat exchanger 94a are disposed in series.

[0153] The eighth heat exchanger 94a transfers heat received from the exhaust gas to water to preheat the water. The water may be heated in a liquid state, or a portion of the water may change phase to steam. The eighth heat exchanger 94a is an example of the replenishment unit 44, an example of the heating unit 44a, and an example of the water preheating unit 44b.

[0154] The water preheated in the eighth heat exchanger 94a flows through the water line 46 and moves to the sixth heat exchanger 91. Other configurations than those described above are almost the same as those in the fourth embodiment, so duplicated explanations will be omitted.

[0155] According to this embodiment, the waste heat of the exhaust gas discharged from the cell stack 43 can also be used to preheat water, so that the energy efficiency of the hydrogen production system 40 can be improved overall.

[0156] (First Modification of Fifth Embodiment) In the fifth embodiment, the seventh heat exchanger 94 is connected to the fifth heat exchanger 90 via the water line 46. However, the present invention is not limited to this. Alternatively, the eighth heat exchanger 94a may be connected to the fifth heat exchanger 90 via the water line 46, the eighth heat exchanger 94a and the seventh heat exchanger 94 may be connected via the water line 46, and the seventh heat exchanger 94 and the sixth heat exchanger 91 may be connected via the water line 46. In this case, the water that has been preheated in the eighth heat exchanger 94a may be further preheated in the seventh heat exchanger 94.

[0157] (Variation 2 of Embodiment 5) In Embodiment 5, the seventh heat exchanger 94 and the eighth heat exchanger 94a are configured to be arranged in series, but this is not limited thereto. For example, the seventh heat exchanger 94 and the eighth heat exchanger 94a may be configured to be arranged in parallel. For example, the eighth heat exchanger 94a may be connected to the fifth heat exchanger 90 by the water line 46 but not connected to the seventh heat exchanger 94. In this case, water is preheated in the seventh heat exchanger 94 and the eighth heat exchanger 94a, and then the water is combined and sent to the sixth heat exchanger 91 where it changes phase to steam.

[0158] Sixth Embodiment Next, a sixth embodiment will be described with reference to Fig. 12. An ammonia synthesis apparatus 10f according to this embodiment differs from the first embodiment in that it includes a steam supply source 95, a steam replenishment line 96, and a steam valve 97.

[0159] The steam supply source 95 is a device that generates steam, and can be any device such as a combustion device. The steam supply source 95 may be different from or the same as the external exhaust heat source.

[0160] The steam replenishment line 96 connects the steam supply source 95 with a portion of the steam line 49 between the second steam heater 56 and the steam flow rate regulator 55. Steam supplied from the steam supply source 95 flows through the steam replenishment line 96.

[0161] The steam valve 97 is disposed in the steam replenishment line 96. When the steam valve 97 is opened, steam is replenished from the steam replenishment line 96 to the steam line 49. When the steam valve 97 is closed, the replenishment of steam from the steam replenishment line 96 to the steam line 49 is stopped. The steam valve 97 is an example of the replenishment unit 44.

[0162] According to this embodiment, when there is a shortage of exhaust heat, the replenishment control unit 73a opens the steam valve 97 to replenish steam to the steam line 49. The condition for determining whether there is a shortage of exhaust heat is not particularly limited, and may be, for example, when the temperature of the exhaust heat in the exhaust heat line 12 falls below a predetermined threshold, when the temperature of the steam flowing through the steam line 49 falls below a predetermined threshold, or when the flow rate of the steam flowing through the steam line 49 falls below a predetermined threshold.

[0163] If the exhaust heat is sufficient, the refill control unit 73a closes the steam valve 97.

[0164] The hydrogen production system 40 according to this embodiment includes a steam valve 97 that replenishes steam from an external steam supply source 95 to the cell stack 43 when the amount of waste heat is insufficient for the amount of steam required to generate the steam. According to this embodiment, when the amount of steam is insufficient, the necessary amount of steam can be made up by replenishing the steam itself. This allows the steam to be used effectively without reducing the amount of energy, as compared to when the amount of energy is reduced by converting the steam into electricity, power, or the like. As a result, the energy efficiency of the hydrogen production system 40 as a whole can be improved.

[0165] The present disclosure is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the spirit of the present disclosure.

[0166] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0167] <Others> Features of the present disclosure are as follows. [Item 1] A hydrogen production system (40) comprising: an exhaust heat receiving unit (41) that receives exhaust heat generated from an external exhaust heat source (11); a steam generating unit (42) that generates steam by heating water with the exhaust heat received by the exhaust heat receiving unit; a cell stack (43) that generates hydrogen by electrolyzing the steam generated by the steam generating unit; and a replenishment unit (44) that replenishes heat to the water, the steam, or the steam generating unit, or replenishes steam from an external steam supply source (95) to the cell stack when the amount of exhaust heat is insufficient to generate a required amount of steam. [Item 2] The hydrogen production system according to Item 1, wherein the replenishment unit is a heating unit (44a) that directly or indirectly heats the water or the steam, and the hydrogen production system comprises the heating unit. [Item 3] The hydrogen production system according to Item 2, further comprising a steam line (49) that connects the steam generation unit and the cell stack and through which the steam flows, and a first steam heater (50) that serves as the heating unit and is disposed upstream of the cell stack in the steam line and heats the steam immediately before it is supplied to the cell stack. [Item 4] The hydrogen production system further comprises: an exhaust heat temperature acquisition unit (69) that acquires the temperature of the exhaust heat; a replenishment control unit (73a) that controls the operation of the replenishment unit based on the temperature of the exhaust heat; and a steam line (49) that connects the steam generation unit and the cell stack and through which the steam flows, and the heating unit comprises a second steam heater (56) that is arranged in the steam line downstream of the steam generation unit and heats the steam immediately after it is generated by the steam generation unit, and the replenishment control unit turns on the second steam heater when the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit falls below a second exhaust heat temperature threshold (WT2).[Item 5] The hydrogen production system according to Item 4 further comprises: a water vapor flow rate adjustment unit (55) disposed in the water vapor line between the second water vapor heater and the cell stack, and adjusting the flow rate of the water vapor; and a first flow rate control unit (73b) that controls the water vapor flow rate adjustment unit to reduce the flow rate of the water vapor when the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit falls below a second exhaust heat temperature threshold, and controls the water vapor flow rate adjustment unit to increase the flow rate of the water vapor when the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit exceeds a first exhaust heat temperature threshold (WT1). [Item 6] The hydrogen production system according to item 4 or 5 further comprises: a water line (46) connecting a water supply source (45) and the steam generation unit; a first water pump (47) arranged on the water line and supplying the water to the steam generation unit (42); a second steam temperature acquisition unit (71) arranged on the steam line (49) and acquiring the temperature of the steam downstream of the steam generation unit (42); and a second flow rate control unit (73c) that, when the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit falls below an exhaust heat temperature threshold, adjusts the discharge rate of the first water pump so that the temperature of the steam acquired by the second steam temperature acquisition unit is within a steam temperature range (TR).a bypass line (51) connecting a portion of the water line (46) upstream of the first water pump with a portion of the steam line between the steam generation unit and the steam flow rate regulator; a boiler (53) arranged in the bypass line and configured to heat the water to generate steam; a bypass valve (54) arranged in the bypass line downstream of the boiler and configured to adjust the flow rate of the steam; a steam pressure acquisition unit (72) acquiring the pressure of the steam flowing through a portion of the bypass line downstream of the bypass valve; and a bypass valve control unit (73e) configured to adjust the aperture of the bypass valve so that the pressure of the steam acquired by the steam pressure acquisition unit falls within a steam pressure range (PR) when the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit falls below a exhaust heat temperature threshold. [Item 8] The hydrogen production system according to any one of Items 4 to 7, further comprising: a steam flow rate regulator arranged in the steam line to regulate the flow rate of the steam; an emergency stop steam line (65) connecting a portion of the steam line upstream of the steam flow rate regulator to a water supply source; an emergency stop valve (66) arranged in the emergency stop steam line; an emergency stop radiator (67) arranged in the emergency stop steam line to cool the steam and produce water; and an emergency stop control unit (73f) that, when the cell stack is brought to an emergency stop, opens the emergency stop valve and controls the steam flow rate regulator to stop the supply of steam to the cell stack, and produces water from the steam using the emergency stop radiator.[Item 9] The hydrogen production system further comprises: a heat transfer line (80) connecting the exhaust heat receiving unit and the steam generating unit; a heat medium that circulates through the heat transfer line and transfers heat from the exhaust heat receiving unit to the steam generating unit; a heat medium temperature acquisition unit (93) that acquires the temperature of the heat medium circulating through the heat transfer line (80); and a replenishment control unit that controls the operation of the replenishment unit based on the temperature of the heat medium, wherein the replenishment unit is a heat medium heater (92) that is arranged on the heat transfer line and heats the heat medium, and the replenishment control unit turns on the heat medium heater when the temperature of the heat medium acquired from the heat medium temperature acquisition unit falls below a heat medium temperature threshold (MT). [Item 10] The hydrogen production system according to item 1 or 2, wherein an exhaust heat line through which the exhaust heat is transferred is connected to the external exhaust heat source, and the replenishment unit is a water preheating unit (44b) that is arranged in the exhaust heat line downstream of the exhaust heat receiving unit and receives the exhaust heat and preheats the water before it is circulated to the steam production unit. [Item 11] The hydrogen production system according to item 1 or 2, wherein a product gas line (57) through which a product gas containing the hydrogen generated by the cell stack flows is connected to the cell stack, and the replenishment unit is a water preheating unit that is arranged in the product gas line and preheats the water by heat of the product gas before it is circulated to the steam production unit. [Item 12] The hydrogen production system according to Item 1 or 2, further comprising an exhaust line (75) connected to the cell stack and through which exhaust gas discharged from the cell stack flows, and the replenishment unit is a water preheating unit disposed in the exhaust line and preheating the water by heat of the exhaust gas before it is circulated to the steam generation unit.[Item 13] The hydrogen production system according to any one of Items 1 to 11, wherein the external exhaust heat source is a hydrogen compound synthesis apparatus or a power plant, and the exhaust heat is: in the hydrogen compound synthesis apparatus, reaction heat generated when synthesizing the hydrogen compounds in the hydrogen compound synthesis apparatus or heat of an outlet gas containing the hydrogen compounds produced by the hydrogen compound synthesis apparatus, and in the power plant, geothermal heat if the power plant is a geothermal power plant, heat of a cooling heat medium if the power plant is a nuclear power plant, or heat of turbine cooling water or heat of combustion gas after burning fuel if the power plant is a thermal power plant. [Item 14] The hydrogen production system according to Item 13, wherein the external exhaust heat source is a hydrogen compound synthesis apparatus, and an exhaust heat line through which the exhaust heat is transferred is connected to the external exhaust heat source, and a raw material gas preheating unit (13) is disposed in the exhaust heat line to supply the exhaust heat to the raw material gas supplied to the hydrogen compound synthesis apparatus. [Item 15] The hydrogen production system according to Item 14, further comprising: an exhaust heat temperature acquisition unit disposed in the exhaust heat line at a position between the external exhaust heat source and the raw material gas preheating unit and configured to acquire a temperature of the exhaust heat; and a replenishment control unit configured to control operation of the replenishment unit based on the temperature of the exhaust heat.

Claims

1. A hydrogen production system (40) comprising: an exhaust heat receiving unit (41) that receives exhaust heat generated from an external exhaust heat source (11); a steam generating unit (42) that generates steam by heating water with the exhaust heat received by the exhaust heat receiving unit; a cell stack (43) that generates hydrogen by electrolyzing the steam generated by the steam generating unit; and a replenishment unit (44) that replenishes heat to the water, the steam, or the steam generating unit, or replenishes steam from an external steam supply source (95) to the cell stack when the amount of exhaust heat is insufficient for generating the required amount of steam.

2. The hydrogen production system according to claim 1, wherein the replenishment unit is a heating unit (44a) that directly or indirectly heats the water or the steam, and the hydrogen production system is equipped with the heating unit.

3. The hydrogen production system according to claim 2, further comprising a steam line (49) that connects the steam generation unit and the cell stack and through which the steam flows, and a first steam heater (50) as the heating unit that is arranged on the steam line upstream of the cell stack and heats the steam immediately before it is supplied to the cell stack.

4. The hydrogen production system further comprises: an exhaust heat temperature acquisition unit (69) that acquires the temperature of the exhaust heat; a replenishment control unit (73a) that controls the operation of the replenishment unit based on the temperature of the exhaust heat; a steam line (49) that connects the steam generation unit and the cell stack and through which the steam flows; and a second steam heater (56) as the heating unit that is arranged in the steam line downstream of the steam generation unit and heats the steam immediately after it is generated by the steam generation unit; and the replenishment control unit turns on the second steam heater when the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit falls below a second exhaust heat temperature threshold (WT2).

5. The hydrogen production system according to claim 4, further comprising: a water vapor flow rate adjustment unit (55) disposed in the water vapor line between the second water vapor heater and the cell stack, and adjusting the flow rate of the water vapor; and a first flow rate control unit (73b) that controls the water vapor flow rate adjustment unit to reduce the flow rate of the water vapor when the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit falls below a second exhaust heat temperature threshold, and controls the water vapor flow rate adjustment unit to increase the flow rate of the water vapor when the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit exceeds a first exhaust heat temperature threshold (WT1).

6. The hydrogen production system according to claim 4, further comprising: a water line (46) connecting a water supply source (45) and the steam generation unit; a first water pump (47) arranged on the water line and supplying the water to the steam generation unit (42); a second steam temperature acquisition unit (71) arranged on the steam line (49) and acquiring the temperature of the steam downstream of the steam generation unit (42); and a second flow rate control unit (73c) that adjusts the discharge rate of the first water pump based on the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit so that the temperature of the steam acquired by the second steam temperature acquisition unit is within a predetermined steam temperature range (TR).

7. The hydrogen production system according to claim 5, further comprising: a water line connecting a water supply source and the steam generation unit; a first water pump arranged on the water line and supplying the water to the steam generation unit; a bypass line (51) connecting a portion of the water line (46) upstream of the first water pump with a portion of the steam line between the steam generation unit and the steam flow rate adjustment unit; a boiler (53) arranged on the bypass line and heating the water to generate steam; a bypass valve (54) arranged on the bypass line downstream of the boiler and adjusting the flow rate of the steam; a steam pressure acquisition unit (72) acquiring the pressure of the steam flowing through the portion of the bypass line downstream of the bypass valve; and a bypass valve control unit (73e) adjusting the opening of the bypass valve based on the temperature of the exhaust heat acquired by the exhaust heat temperature acquisition unit so that the pressure of the steam acquired by the steam pressure acquisition unit is within a predetermined steam pressure range (PR).

8. The hydrogen production system according to claim 5, further comprising: a steam flow rate regulator disposed in the steam line for regulating the flow rate of the steam; an emergency stop steam line (65) connecting a portion of the steam line upstream of the steam flow rate regulator with a water supply source; an emergency stop valve (66) disposed in the emergency stop steam line; an emergency stop radiator (67) disposed in the emergency stop steam line for cooling the steam to produce water; and an emergency stop control unit (73f) which, in the event of an emergency stop of the cell stack, opens the emergency stop valve and controls the steam flow rate regulator to stop the supply of steam to the cell stack, and produces water from the steam using the emergency stop radiator.

9. The hydrogen production system further comprises: a heat transfer line (80) connecting the exhaust heat receiving unit and the steam generation unit; a heat medium that circulates through the heat transfer line and transfers heat from the exhaust heat receiving unit to the steam generation unit; a heat medium temperature acquisition unit (93) that acquires the temperature of the heat medium circulating through the heat transfer line 80; and a replenishment control unit that controls the operation of the replenishment unit based on the temperature of the heat medium, wherein the replenishment unit is a heat medium heater (92) arranged on the heat transfer line and heats the heat medium, and the replenishment control unit turns on the heat medium heater when the temperature of the heat medium acquired from the heat medium temperature acquisition unit falls below a heat medium temperature threshold (MT).

10. A hydrogen production system as described in claim 1 or 2, wherein an exhaust heat line through which the exhaust heat is transferred is connected to the external exhaust heat source, and the replenishment unit is a water preheating unit (44b) that is arranged downstream of the exhaust heat receiving unit in the exhaust heat line and receives the exhaust heat and preheats the water before it is circulated to the steam generation unit.

11. The hydrogen production system according to claim 1 or 2, further comprising a product gas line (57) connected to the cell stack and through which a product gas containing the hydrogen produced by the cell stack flows, and the replenishment unit is a water preheating unit disposed in the product gas line and preheating the water by heat of the product gas before it is circulated to the steam generation unit.

12. The hydrogen production system according to claim 1 or 2, further comprising an exhaust line (75) connected to the cell stack and through which exhaust gas discharged from the cell stack flows, and the replenishment unit is a water preheating unit disposed in the exhaust line and preheating the water by heat of the exhaust gas before it is circulated to the steam generation unit.

13. The hydrogen production system according to claim 1 or 2, wherein the external exhaust heat source is a hydrogen compound synthesis apparatus or a power plant, and the exhaust heat is: in the hydrogen compound synthesis apparatus, the reaction heat generated when the hydrogen compounds are synthesized in the hydrogen compound synthesis apparatus, or the heat of an outlet gas containing the hydrogen compounds produced by the hydrogen compound synthesis apparatus; in the power plant, the exhaust heat is geothermal heat if the power plant is a geothermal power plant, the heat of a cooling medium if the power plant is a nuclear power plant, or the heat of turbine cooling water or the heat of combustion gas after burning fuel if the power plant is a thermal power plant.

14. A hydrogen production system as described in claim 13, wherein the external exhaust heat source is a hydrogen compound synthesis device, an exhaust heat line through which the exhaust heat is transferred is connected to the external exhaust heat source, and a raw material gas preheating section (13) is disposed in the exhaust heat line to supply the exhaust heat to the raw material gas supplied to the hydrogen compound synthesis device.

15. The hydrogen production system according to claim 14, further comprising: an exhaust heat temperature acquisition unit disposed in the exhaust heat line at a position between the external exhaust heat source and the raw material gas preheating unit, for acquiring the temperature of the exhaust heat; and a replenishment control unit for controlling the operation of the replenishment unit based on the temperature of the exhaust heat.

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