Hydrogen gas production apparatus, hydrogen gas supply apparatus, fuel cell system, mobile device, and hydrogen gas production method

Abstract

The present invention provides a compact and simple hydrogen gas production apparatus that efficiently decomposes ammonia during startup when producing hydrogen gas from ammonia as a raw material, removes nitrogen without using a high-pressure compressor, consumes little power, and is suitable for hydrogen gas production. [Solution] The hydrogen gas production apparatus of the embodiment comprises a heating unit for raising the temperature of ammonia gas to a decomposition temperature, an ammonia decomposition unit for decomposing ammonia gas by contacting it with a catalyst, and a primary purification unit and a secondary purification unit for removing residual ammonia gas and nitrogen gas from the decomposed ammonia gas. The heating unit for raising the temperature has a first electric heater for heating liquefied ammonia or ammonia gas using electricity, and heating of liquefied ammonia or ammonia gas by the first electric heater is performed during the start-up period after the start of operation of the hydrogen gas production apparatus until permeate gas exceeding a predetermined flow rate is discharged from the hydrogen separation unit.

Description

[Technical Field]

[0001] The present invention relates to a hydrogen gas production apparatus, a hydrogen gas supply apparatus, a fuel cell system, a mobile device, and a hydrogen gas production method for producing hydrogen gas using ammonia as a raw material. [Background technology]

[0002] Due to the trend toward carbon neutrality, fuel cells are widely used in fuel cell vehicles (FCVs) and on-site facilities for home and commercial use. As a method that does not generate carbon dioxide when producing hydrogen gas, which is the fuel gas for fuel cells, a method of producing hydrogen gas using ammonia as a raw material is known. In this method, ammonia gas heated to a high temperature is brought into contact with a catalyst and decomposed to produce a mixed gas (ammonia decomposition gas) consisting mainly of hydrogen gas and nitrogen gas.

[0003] Ammonia decomposition gas contains nitrogen gas as well as undecomposed residual ammonia. When residual ammonia is supplied to the negative electrode (fuel electrode) of a fuel cell along with hydrogen gas, the platinum catalyst at the negative electrode becomes poisoned, reducing its catalytic activity and thus lowering the power generation performance of the fuel cell. Therefore, it is preferable to sufficiently remove the ammonia remaining in the ammonia decomposition gas. Conventionally, it is known to remove ammonia from the ammonia decomposition gas by adsorbing it with an adsorbent such as zeolite (for example, Non-Patent Documents 1 and 3, and Patent Documents 1 to 3).

[0004] Furthermore, if nitrogen gas is not removed from the ammonia decomposition gas, the maximum output during power generation will decrease; therefore, it is preferable to remove nitrogen gas from the ammonia decomposition gas. Conventionally, it is known to remove nitrogen gas from ammonia decomposition gas using methods such as pressure swing (PSA) or cryogenic separation (for example, Non-Patent Documents 1 and 2, and Patent Document 3).

[0005] Furthermore, it is known that after adsorbing and removing unreacted residual ammonia from the ammonia decomposition gas and separating most of the hydrogen gas, the remaining hydrogen gas remains with nitrogen gas without being separated (for example, Patent Document 4). Patent Document 4 describes heating this residual gas and using it as a regeneration gas for the adsorbent that has adsorbed residual ammonia. Furthermore, Patent Document 4 discloses burning the residual gas used as a regeneration gas and using the resulting combustion gas as a heat source for ammonia decomposition and adsorbent regeneration. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2017-104778 [Patent Document 2] International Publication No. 2023 / 022995 [Patent Document 3] Japanese Patent Publication No. 126689 / 1989 [Patent Document 4] International Publication No. 2018 / 116982 [Non-patent literature]

[0007] [Non-Patent Document 1] Taiyo Nippon Sanso Corporation, Cabinet Office, Strategic Innovation Promotion Program (SIP), Project "Energy Carriers," Research Theme "Basic Technology for Ammonia Hydrogen Stations," Completion Report (for Public Release), March 25, 2019. [Non-Patent Document 2] Akihiro Numata, "Hydrogen Recovery by Cryogenic Separation Method," Hitachi Review, Vol. 53, No. 12, p. 1164-1971 (1971) [Non-Patent Document 3] Junyoung Cha et al., “Ammonia as an efficient COx-free hydrogen carrier Fundamentals and feasibility analyzes for fuel cell applications”, Applied Energy, Vol. 224, p. 194-204 (2018) [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the hydrogen production processes using liquefied ammonia as a raw material described in Patent Documents 1 and 3 and Non-Patent Document 1, a method is disclosed for producing purified hydrogen by removing residual ammonia by adsorption using an adsorbent after generating hydrogen by catalytic decomposition of ammonia, and separating and removing nitrogen by the PSA method or cryogenic separation method. The purified hydrogen obtained by these methods can be used as fuel for polymer electrolyte fuel cells (PEFCs), which are widely used as small, highly efficient power generation systems. Non-Patent Document 2 discloses details of the related cryogenic separation method. However, nitrogen removal by the PSA method and cryogenic separation method generally requires a high-pressure compressor and space for its installation. Furthermore, in the PSA method, nitrogen removal is performed by repeatedly adsorbing nitrogen onto an adsorbent under pressure and desorbing and discharging nitrogen from the adsorbent under reduced pressure, so the compressor must be started and kept running frequently. Therefore, the power consumption is large. Similarly, in the cryogenic separation method, nitrogen is liquefied or adsorbed onto an adsorbent and separated and removed under even higher pressure conditions or cooling conditions using adiabatic expansion from a high-pressure state, so the power consumption is also very large. Performing PSA or cryogenic separation methods, which require such operations, necessitates large-scale equipment, making it difficult to mount or install them on mobile devices or small on-site facilities.

[0009] On the other hand, the hydrogen production process using liquefied ammonia as a raw material, as described in Non-Patent Literature 3, consists only of a hydrogen production step by catalytic decomposition of ammonia and a subsequent step of removing residual ammonia gas by adsorption using an adsorbent, omitting the nitrogen separation step by the aforementioned PSA method or cryogenic separation method, which consume a lot of power and require large-scale equipment. According to the hydrogen production process in Non-Patent Literature 3, the residual ammonia gas that poisons the negative electrode catalyst of a polymer electrolyte fuel cell (PEFC) is removed from the produced hydrogen, so the produced hydrogen can be used as fuel for the fuel cell (PEFC), and it consumes little power, can be mounted or installed on a mobile device or small on-site equipment, and allows for miniaturization and weight reduction of the equipment. However, since nitrogen separation is not performed in the process in Non-Patent Literature 3, nitrogen equivalent to a molar ratio of hydrogen:nitrogen = 75:25 remains in the produced hydrogen. Therefore, in the process in Non-Patent Literature 3, when the produced hydrogen is supplied to a fuel cell (PEFC) for power generation, the presence of nitrogen increases concentration polarization due to the decrease in hydrogen concentration at the negative electrode, leading to a significant decrease in power generation efficiency, especially at high output.

[0010] Furthermore, Patent Document 2, similar to Non-Patent Document 3, describes a hydrogen production process that omits the aforementioned nitrogen separation step and consists only of a hydrogen production step by catalytic decomposition of ammonia and an adsorption removal step for residual ammonia gas. The hydrogen containing nitrogen is then supplied to a fuel cell (PEFC) for power generation. In particular, the document discloses methods to improve the decrease in power generation efficiency by modifying the negative electrode of the fuel cell (PEFC), such as cutting grooves into it, or by intermittently purging the nitrogen that accumulates at high concentrations in the negative electrode during power generation. However, even with these methods, the decrease in power generation efficiency due to increased concentration polarization is essentially unavoidable, and a special fuel cell (PEFC) with specifications different from those generally available on the market is required, posing a problem in terms of versatility.

[0011] By the way, in order to increase the decomposition rate of ammonia gas, it is preferable that the temperature is sufficiently high when the ammonia gas comes into contact with the catalyst. Therefore, it is preferable that the heat source used for heating the ammonia gas is continuously supplied. Patent Document 4 discloses using the combustion gas of the residual gas used for regenerating the adsorbent as the heat source for ammonia decomposition. However, at the start-up of the hydrogen production apparatus, since hydrogen gas has not yet been generated or the amount is small even if it has been generated, the heat source for heating the ammonia gas is insufficient. Therefore, if only the above combustion gas is used as the heat source for ammonia decomposition, it takes time until the decomposition rate of ammonia increases. Therefore, it takes time to obtain hydrogen gas, and the productivity of hydrogen gas decreases.

[0012] An object of the present invention is to provide a hydrogen gas production apparatus that can efficiently decompose ammonia at startup when producing hydrogen gas using ammonia as a raw material, can remove nitrogen without using a high-pressure compressor, consumes less power, and is small and simple, and to provide a hydrogen gas supply apparatus, a fuel cell system, a moving body, and a hydrogen gas production method.

Means for Solving the Problems

[0013] This disclosure includes the following aspects. Aspect 1 A hydrogen gas production apparatus for producing hydrogen gas by sequentially flowing in one direction an ammonia gas which is either the gas obtained by vaporizing the liquefied ammonia or the boil-off gas of the liquefied ammonia while flowing the liquefied ammonia or the boil-off gas of the liquefied ammonia as a raw material, the decomposition gas obtained by decomposing the ammonia gas, and the purified gas obtained by purifying the decomposition gas, comprising: A heating unit for heating at least the ammonia gas among the liquefied ammonia and the ammonia gas, and raising the temperature of the ammonia gas to a temperature equal to or higher than the decomposition temperature; An ammonia decomposition unit that contacts the ammonia gas heated to the decomposition temperature with a catalyst to decompose it, generating a decomposition gas containing hydrogen gas, nitrogen gas, and residual ammonia gas, and discharging it to the downstream side; A primary purification unit that is disposed downstream of the ammonia decomposition unit, removes one of the residual ammonia gas and the nitrogen gas from the decomposed gas to generate a primary purified gas, and discharges it downstream; A secondary purification unit that is disposed downstream of the primary purification unit, removes the other of the residual ammonia gas and the nitrogen gas from the primary purified gas to generate a secondary purified gas, and discharges it downstream, and is provided with: Among the primary purification unit and the secondary purification unit, the purification unit from which the residual ammonia gas is removed is an ammonia adsorption unit having an adsorbent that adsorbs the residual ammonia gas; Among the primary purification unit and the secondary purification unit, the purification unit from which the nitrogen gas is removed has a separation membrane, and the separation membrane is permeated through the separation membrane by a differential pressure created between the upstream side and the downstream side of the separation membrane. The decomposed gas or the primary purified gas is separated into a permeated gas containing most of the hydrogen gas and a residual gas containing the remaining hydrogen gas and the nitrogen gas remaining on the upstream side of the separation membrane without passing through the separation membrane, and is discharged. It is a hydrogen separation unit configured as follows: The heating unit for temperature increase has a first electric heater that heats the liquefied ammonia or the ammonia gas using electric power, and after the start of operation of the hydrogen gas production apparatus, until a permeated gas exceeding a predetermined flow rate is discharged from the hydrogen separation unit. During the start-up period, the liquefied ammonia or the ammonia gas is heated by the first electric heater, a hydrogen gas production apparatus.

[0014] Aspect Ⅱ The heating unit for temperature increase further has a combustor that burns the residual gas discharged from the hydrogen separation unit together with air and discharges the combustion gas, and a first heat exchange heater that heats the ammonia gas by heat exchange with the combustion gas discharged from the combustor. During the steady operation period that starts when a permeated gas exceeding a predetermined flow rate is discharged from the hydrogen separation unit, the ammonia gas is heated by the first heat exchange heater, the hydrogen gas production apparatus according to Aspect Ⅰ.

[0015] Aspect Ⅲ The hydrogen gas production apparatus according to embodiment 2, wherein the heating unit for raising the temperature continuously or gradually reduces the output of the first electric heater after the start of the steady-state operation period.

[0016] Pattern 4 The first electric heater heats the liquefied ammonia or ammonia gas flowing upstream of the ammonia decomposition section. The hydrogen gas production apparatus according to embodiment 2 or 3, wherein the heating unit for raising the temperature further includes a second electric heater that uses electricity to adjust the temperature of the ammonia gas flowing through the ammonia decomposition unit.

[0017] Appearance 5 The hydrogen gas production apparatus according to embodiment 4, wherein the heating unit for raising the temperature stops heating the liquefied ammonia or ammonia gas by the first electric heater during the steady-state operation period, and then heats the ammonia gas by the first heat exchange heater and the second electric heater.

[0018] Appearance 6 The heating unit for raising the temperature further comprises a second heat exchange heater that vaporizes the liquefied ammonia by heat exchange with the decomposition gas, and a third electric heater that heats the liquefied ammonia using electricity. The hydrogen gas production apparatus according to any one of embodiments 1 to 5, wherein the first electric heater heats the gas obtained by vaporizing the liquefied ammonia.

[0019] Appearance 7 The hydrogen gas production apparatus according to embodiment 6, wherein the heating unit for raising the temperature heats the liquefied ammonia with the third electric heater during the period from the start of operation of the hydrogen gas production apparatus until the decomposition gas exceeding a predetermined flow rate is discharged from the ammonia decomposition unit.

[0020] Appearance 8 The hydrogen gas production apparatus according to embodiment 7, wherein the liquefied ammonia is heated by the second heat exchange heater during a period that begins when the decomposition gas exceeding a predetermined flow rate is discharged from the ammonia decomposition unit.

[0021] Appearance 9 The hydrogen gas production apparatus according to embodiment 8, wherein the heating unit for raising the temperature reduces the output of the third electric heater continuously or in stages after the start of the period which begins when the decomposition gas exceeding a predetermined flow rate is discharged from the ammonia decomposition unit.

[0022] Appearance 10 The heating unit for raising the temperature further comprises a combustor that burns the residual gas discharged from the hydrogen separation unit together with air and discharges the combustion gas, and a first heat exchange heater that heats the ammonia gas by heat exchange with the combustion gas discharged from the combustor. The hydrogen gas production apparatus according to any one of embodiments 1 to 9, wherein the combustor burns at least one of the ammonia gas extracted upstream of the ammonia decomposition unit and the decomposition gas or the purified gas extracted downstream of either the ammonia decomposition unit or the ammonia decomposition unit together with the residual gas.

[0023] Appearance 11 The hydrogen gas production apparatus according to any one of embodiments 1 to 10, wherein the permeate gas contains 70 to 80 volume percent of the hydrogen gas in the primary purified gas.

[0024] Appearance 12 A hydrogen gas production apparatus according to any one of embodiments 2 to 5, 10, or 11, wherein the residual gas discharged from the hydrogen separation unit is led to the combustor without passing through the ammonia adsorption unit.

[0025] Appearance 13 The hydrogen gas production apparatus according to any one of claims 2 to 5, 10, 11, or 12, wherein the residual gas discharged from the hydrogen separation unit is guided to the combustor without being heated.

[0026] Appearance 14 The ammonia adsorption section is, A plurality of upstream ammonia adsorbents arranged in parallel in the aforementioned one direction, It comprises at least one upstream ammonia adsorbent and at least one downstream ammonia adsorbent arranged in series in one direction, A hydrogen gas production apparatus according to any one of embodiments 1 to 13, wherein each of the ammonia adsorbents has the adsorbent.

[0027] Appearance 15 The separation membrane is made of polymer or ceramic. The hydrogen gas production apparatus according to any one of embodiments 1 to 14, wherein the differential pressure is 0.3 to 0.9 MPa.

[0028] Appearance 16 The ammonia adsorption unit comprises a regeneration heater for heating the adsorbent that has adsorbed the residual ammonia gas, and an inert gas introduction line for introducing an inert gas from the outside, and is configured to release the residual ammonia gas adsorbed on the adsorbent from the adsorbent by heating with the regeneration heater, and to discharge it together with the inert gas introduced through the inert gas introduction line, according to any one of embodiments 1 to 15.

[0029] Appearance 17 A hydrogen gas production apparatus according to any one of embodiments 1 to 16, A hydrogen gas supply device comprising a purified gas tank for storing the secondary purified gas produced in the hydrogen gas production apparatus.

[0030] Appearance 18 A hydrogen gas production apparatus according to any one of embodiments 1 to 16, or a hydrogen gas supply apparatus according to embodiment 17, A fuel cell system comprising a polymer electrolyte fuel cell having a negative electrode and a positive electrode, wherein the negative electrode and the positive electrode are connected to an external load, and the system is configured to generate electricity by supplying a secondary purified gas produced in the hydrogen gas production device or the hydrogen gas supply device to the negative electrode and air to the positive electrode.

[0031] Appearance 19 It is a mobile object, The fuel cell system described in aspect 18, A mobile body comprising: a motor connected to the negative and positive electrodes of a polymer electrolyte fuel cell in the fuel cell system, which is driven by electricity generated by the fuel cell in the fuel cell system and generates power to propel the mobile body.

[0032] Appearance 20 The mobile body according to embodiment 19, further comprising a secondary battery connected in parallel with the motor to the solid polymer fuel cell.

[0033] Appearance 21 A method for producing hydrogen gas, comprising sequentially flowing liquefied ammonia or the boil-off gas of liquefied ammonia as a raw material, ammonia gas which is either the gas obtained by vaporizing the liquefied ammonia or the boil-off gas, a decomposition gas obtained by decomposing the ammonia gas, and a purified gas obtained by purifying the decomposition gas in one direction, A heating step in which at least the ammonia gas is heated from the liquefied ammonia and the ammonia gas, and the ammonia gas is heated to a temperature above the decomposition temperature, The ammonia decomposition step involves bringing the ammonia gas, heated to the aforementioned decomposition temperature, into contact with a catalyst to decompose it, generating a decomposition gas containing hydrogen gas, nitrogen gas, and residual ammonia gas, and discharging it downstream. A primary purification step involves removing either the residual ammonia gas or the nitrogen gas from the decomposition gas to produce a primary purified gas, which is then discharged downstream. The process includes a secondary purification step of removing the residual ammonia gas and the other of the nitrogen gas from the primary purified gas to produce a secondary purified gas, which is then discharged downstream. The purification step among the primary and secondary purification steps that removes the residual ammonia gas is an ammonia adsorption step in which the residual ammonia gas is adsorbed onto an adsorbent. The purification step of the primary purification step and the secondary purification step that removes the nitrogen gas is a hydrogen separation step that uses a separation membrane configured to separate the decomposition gas or the primary purified gas into a permeate gas containing most of the hydrogen gas that has permeated the separation membrane and a residual gas containing the remainder of the hydrogen gas and the nitrogen gas that remains on the upstream side of the separation membrane without permeating the separation membrane, and discharge the separated gas, by the differential pressure created between the upstream and downstream sides of the separation membrane. A method for producing hydrogen gas, wherein in the heating step, during the start-up period from the start of hydrogen gas production until the permeate gas exceeding a predetermined flow rate is discharged from the separation membrane, the liquefied ammonia or ammonia gas is heated using electricity by a first electric heater. [Effects of the Invention]

[0034] According to the hydrogen gas production apparatus and hydrogen gas production method of the above embodiment, when producing hydrogen gas using ammonia as a raw material, the decomposition of ammonia at the start of hydrogen gas production can be efficiently carried out, nitrogen can be removed without using a high-pressure compressor, thereby reducing power consumption and making the equipment smaller and simpler. Furthermore, a hydrogen gas supply device, fuel cell system, and mobile unit equipped with such a hydrogen gas production apparatus can be obtained. [Brief explanation of the drawing]

[0035] [Figure 1] This diagram shows the configuration of a hydrogen gas production apparatus A1 in one embodiment. [Figure 2] This diagram shows the configuration of a hydrogen gas production apparatus A2 according to one embodiment. [Figure 3] This diagram shows the configuration of a hydrogen gas production apparatus A3 in one embodiment. [Figure 4] This diagram shows the configuration of a hydrogen gas production apparatus A4 according to one embodiment. [Figure 5] This diagram shows the configuration of a hydrogen gas production apparatus A5 in one embodiment. [Figure 6] This diagram shows the configuration of a hydrogen gas production apparatus A6 according to one embodiment. [Figure 7] This diagram shows the configuration of a hydrogen gas production apparatus A7 according to one embodiment. [Figure 8] This figure shows the configuration of a hydrogen gas supply device B1 according to one embodiment. [Figure 9] This figure shows the configuration of a hydrogen gas supply device B2 according to one embodiment. [Figure 10] This diagram shows the configuration of a fuel cell system C1 in one embodiment. [Figure 11] This figure shows the configuration of a fuel cell system C2 in one embodiment. [Figure 12] This figure shows the configuration of a fuel cell system C3 in one embodiment. [Figure 13] This diagram shows the configuration of a fuel cell system C4 in one embodiment. [Figure 14] This diagram shows the configuration of a fuel cell system C5 in one embodiment. [Figure 15] This diagram shows the configuration of a fuel cell system C6 in one embodiment. [Figure 16] This is a diagram showing the configuration of a fuel cell system C7 in one embodiment. [Figure 17] This figure shows the configuration of a fuel cell system C8 in one embodiment. [Modes for carrying out the invention]

[0036] The following describes the hydrogen gas production apparatus, hydrogen gas supply apparatus, fuel cell system, mobile unit, and hydrogen gas production method according to the embodiment.

[0037] Figure 1 shows the configuration of a hydrogen gas production apparatus A1 according to one embodiment. In the following description, hydrogen gas production apparatus An (where n is an integer from 1 to 7) may be collectively referred to as hydrogen gas production apparatus A.

[0038] Hydrogen gas production apparatus A1 is a device that produces hydrogen gas by sequentially flowing ammonia gas (either the gas obtained by vaporizing liquefied ammonia or the boil-off gas) in one direction, along with decomposition gas obtained by decomposing ammonia gas, and purified gas obtained by purifying the decomposition gas, while using liquefied ammonia or boil-off gas of liquefied ammonia as a raw material.

[0039] The raw material for hydrogen gas can be either liquefied ammonia or its boil-off gas, or both. In the following explanation, the case in which liquefied ammonia is used as the raw material for hydrogen gas will be explained as a representative example. One-way means the direction in which at least one of liquefied ammonia and boil-off gas, ammonia gas, decomposition gas, and purified gas, flows through each part (including lines and equipment) that constitutes the hydrogen gas production apparatus A1 (hereinafter also referred to as the gas flow direction).

[0040] The hydrogen gas production apparatus A1 comprises a heating unit 8 for raising the temperature, an ammonia decomposition unit 9, a primary purification unit 15, and a secondary purification unit 19. More specifically, the hydrogen gas production apparatus A1 comprises a tank 1, a raw ammonia line 3, a heating unit 8 for raising the temperature, an ammonia decomposition unit 9, a decomposition gas line 11, a cooler 13, a primary purification unit 15, a primary purification gas line 17, a secondary purification unit 19, a secondary purification gas line 21, and a vacuum pump 22.

[0041] Tank 1 is a container for storing liquefied ammonia. The ammonia used to make liquefied ammonia may be synthesized using the Haber-Bosch process, for example, using hydrogen gas obtained from natural gas, coal gas, etc., through a steam reforming reaction or a shift reaction, and nitrogen gas from the air as raw materials, or it may be synthesized using hydrogen gas obtained by water electrolysis and nitrogen gas from the air as raw materials; the synthesis method is not limited. Tank 1 generally includes a nozzle with an openable and closable valve for replenishing the amount of liquefied ammonia inside from the outside when the amount decreases (not shown).

[0042] It is preferable that the liquefied ammonia stored in tank 1 has had components such as carbon monoxide, hydrogen sulfide, and sulfur compounds such as sulfur dioxide thoroughly removed beforehand. The secondary purified gas produced by the hydrogen gas production apparatus A1 using liquefied ammonia as a raw material, as described later, mainly consists of hydrogen gas and is used, for example, as fuel gas for polymer electrolyte fuel cells (PEFCs). In this case, if the above-mentioned components are contained as impurities in the secondary purified gas, the negative electrode of the PEFC may be poisoned, and the power generation performance may decrease. Therefore, it is preferable that the liquefied ammonia stored in tank 1 has had impurities thoroughly removed to the extent that electrode poisoning does not become a problem. Ammonia obtained by synthesizing hydrogen gas obtained by water electrolysis with nitrogen gas is less likely to contain the above-mentioned impurities and is therefore preferable as liquefied ammonia to be used as a raw material for secondary purified gas. Ammonia synthesized from raw materials such as natural gas and coal gas by the Haber-Bosch process can also generally have the amount of the above-mentioned impurities suppressed to an acceptable level by thoroughly controlling the purity at each stage of the synthesis.

[0043] Liquefied ammonia is stored in tank 1 such that a gas phase space filled with vaporized ammonia gas is formed above the liquid surface, and the liquid phase liquefied ammonia and the gas phase ammonia gas form a gas-liquid equilibrium state at the temperature inside tank 1. During operation of hydrogen gas production apparatus A1, tank 1 is normally sealed except for the supply valve 4, which will be described later. During operation of hydrogen gas production apparatus A1, the gas phase pressure inside tank 1 (hereinafter also referred to as tank pressure) is maintained at the saturated vapor pressure of ammonia at the temperature inside tank 1, except in cases such as when the supply amount of liquefied ammonia fluctuates rapidly. As will be described later, this tank pressure becomes part of the driving force that moves the gas within the system during the process of producing hydrogen gas from liquefied ammonia in hydrogen gas production apparatus A1.

[0044] The raw ammonia line 3 is a line that guides liquefied ammonia from tank 1 to the downstream side. In this specification, a line may include piping and may also include valves provided in the piping. The raw ammonia line 3 is provided with a supply valve 4 that opens when liquefied ammonia from tank 1 is supplied to the downstream side. In the drawings, lines that are partially interrupted, such as the raw ammonia line 3, are considered to be the same line if they appear at the same height or horizontal position.

[0045] The heating section 8 is the part that heats at least the ammonia gas from the liquefied ammonia and ammonia gas, raising the temperature of the ammonia gas to the decomposition temperature. The heating section 8 has a vaporization heater (hereinafter simply referred to as the vaporizer) 5 and a heating section 7.

[0046] The vaporizer 5 is installed in the raw ammonia line 3 and is a device that vaporizes liquefied ammonia into ammonia gas. The vaporizer 5 is equipped with a heating mechanism and can supply a larger amount of heat to the liquefied ammonia than the latent heat of vaporization of the liquefied ammonia. The heating mechanism can use a low-temperature side flow path 5b (second heat exchange heater) of a heat exchanger (for example, a second heat exchanger 25) that performs heat exchange between liquefied ammonia and a high-temperature gas, or an electric heater 5a (third electric heater), and these can also be used in combination. The heat exchanger is not limited to the second heat exchanger 25, and if there is an external heat source with sufficient heat quantity and temperature for vaporizing liquefied ammonia, the liquefied ammonia may be vaporized by introducing a fluid heated by that heat source as a heat transfer medium to the heat exchanger of the vaporizer 5 (this embodiment is not shown). This heat exchanger is preferably used in both the startup period and the steady-state operation period (operation excluding the startup period) of the hydrogen gas production apparatus A1.

[0047] The heating element 7 is a device that raises the temperature of the ammonia gas vaporized by the vaporizer 5 to a temperature above the decomposition temperature. The ammonia gas may be raised to the decomposition temperature, or to a temperature above the decomposition temperature. The decomposition temperature is the temperature required for the decomposition reaction of ammonia gas in the ammonia decomposition section 9 (reaction equation 2NH3 → 3H2 + N2), and is set according to the performance of the catalyst, etc., so that a sufficient decomposition rate of ammonia gas can be obtained. Specifically, a temperature above the decomposition temperature refers to a temperature obtained by adding at least a portion of the temperature drop due to endothermic heat loss associated with ammonia decomposition in the ammonia decomposition section 9 to the decomposition temperature. The upper limit of the temperature above the decomposition temperature is, for example, 900°C, 800°C, 700°C, and 600°C, from the viewpoint of producing hydrogen gas without hindrance using the hydrogen gas production apparatus A1.

[0048] The heating unit 8 for temperature rise has a first electric heater. The first electric heater is a device that heats liquefied ammonia or ammonia gas using electric power. In this specification, the electric heater is a heater that performs resistance heating, induction heating, etc. by applying an electric current. Since the first electric heater can heat by applying an electric current, it can perform heating independently of the heating performed by other heaters (for example, the first heat exchange heater) that use hydrogen gas produced by the hydrogen gas production apparatus A1 as a heat source by burning it. Also, since the first electric heater can heat by applying an electric current, it can heat quickly and accurately (easily) compared to heaters using other heating methods. The first electric heater can be an electric heater 7a for heating ammonia gas, the aforementioned electric heater 5a for heating liquefied ammonia, or both. The electric heater 7a functions as a heating unit 7, and the electric heater 5a functions as a vaporizer 5. In the following explanation, the first electric heater will primarily be described using the heating of ammonia gas by electric heater 7a as an example. Therefore, electric heater 7a will be referred to as the first electric heater 7a, and electric heater 5a will be referred to as the third electric heater 5a to distinguish it from the first electric heater 7a.

[0049] The heating unit 8 for temperature increase heats the ammonia gas using the first electric heater 7a during the start-up period after the hydrogen gas production apparatus A1 starts operation, until a predetermined flow rate of permeate gas (described later) is discharged from the hydrogen separation unit 19. During the start-up period of the hydrogen gas production apparatus A1, the combustion gas that serves as the heat source for heating by the first heat exchanger 33 (described later) has not yet been generated, or if it has been generated, the amount is small. Therefore, it is not possible to raise the ammonia gas to the decomposition temperature using the first heat exchanger 33. As a result, if only combustion gas is used as the heat source, the ammonia gas is difficult to heat up, and it takes time for the ammonia decomposition rate to increase. Consequently, it takes time for hydrogen gas to be produced at the desired flow rate, and the productivity of hydrogen gas decreases. According to this embodiment, by heating using the first electric heater 7a during such a start-up period, the ammonia gas can be quickly and easily raised to the decomposition temperature independently of heating by the first heat exchanger 33. Therefore, the ammonia decomposition rate increases early in the hydrogen gas production device A1 after startup, and as a result, hydrogen gas can be obtained at the desired flow rate, thus improving hydrogen gas productivity.

[0050] Preferably, the ammonia gas is heated by the first electric heater 7a to a temperature equal to the decomposition temperature, or at least a portion of the temperature drop due to endothermic reaction associated with ammonia decomposition in the ammonia decomposition section 9, which is added to the decomposition temperature. Since the ammonia decomposition reaction is an endothermic reaction, even if the ammonia gas is heated to the decomposition temperature in the raw ammonia line 3, its temperature may decrease as ammonia decomposition progresses in the ammonia decomposition section 9, and may fall below the decomposition temperature. In such cases, the ammonia gas can be heated by the first electric heater 7a to the aforementioned added temperature, thereby maintaining the decomposition temperature even in the ammonia decomposition section 9 where the temperature has decreased.

[0051] In addition to the first electric heater 7a, the heating element 7 can also be other electric heaters (for example, the second electric heater 7b described later) or a heater for a heat exchanger that performs heat exchange between ammonia gas and a high-temperature gas (for example, the first heat exchange heater 33 described later) (for example, the first heat exchange heater 7c described later), and preferably these are used in combination. The heating element 7 may be installed downstream of the vaporizer 5 in the raw ammonia line 3, as shown in Figure 1 (first electric heater 7a), to heat the ammonia gas flowing in the raw ammonia line 3, or it may be installed in the ammonia decomposition section 9, as shown in Figure 1 (second electric heater 7b), to heat the apparatus of the ammonia decomposition section 9 (for example, the decomposition tower described later), and preferably it is installed in both locations. Since the decomposition reaction of ammonia gas is an endothermic reaction, the temperature decreases in the ammonia decomposition section 9 as the decomposition reaction progresses (positionally, from the upstream side to the downstream side in the ammonia decomposition section 9). Therefore, the heating element 7 (for example, the first electric heater 7a) which is designed to heat the ammonia gas flowing through the raw ammonia line 3 can compensate in advance for at least a portion of the temperature drop that occurs in the ammonia decomposition section 9 by heating the ammonia gas to a temperature that is above the decomposition temperature, thereby compensating for at least a portion of the temperature drop that occurs in the ammonia decomposition section 9 due to endothermic reaction.

[0052] The heat source used for heating by the first heat exchanger 33 is not limited to the combustion gas mentioned above. If there is an external heat source with sufficient heat quantity and temperature to raise the temperature of the ammonia gas, the fluid heated by that heat source can be introduced to the first heat exchanger 33 as a heat transfer medium to raise the temperature to a predetermined decomposition temperature. Such a first heat exchanger 33 is preferably used during both the startup period and the steady-state operation period of the hydrogen gas production apparatus A1. Furthermore, as described above, the combustion gas can also be used as the heat source in the first heat exchanger 33 for heating. In this case, as will be described later, it is preferably used during the steady-state operation period of the hydrogen gas production apparatus A1.

[0053] The ammonia decomposition section 9 is connected to the raw ammonia line 3 downstream of the vaporizer 5. It is the section that decomposes (cracking) ammonia gas heated to the decomposition temperature by contacting it with a catalyst, generating decomposition gas containing hydrogen gas, nitrogen gas, and residual ammonia gas, which is then discharged downstream. Preferably, the ammonia decomposition section 9 uses a decomposition tower that flows ammonia gas from bottom to top while contacting it with a catalyst placed inside to decompose it.

[0054] Preferably, catalysts used for ammonia decomposition include oxides, oxynitrides, or composite oxides or composite oxynitrides of elements such as sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), strontium (St), barium (Ba), rare earth elements (e.g., cerium (Ce), lanthanum (La), yttrium (Y), etc.), aluminum (Al), silicon (Si), titanium (Ti), and zirconium (Zr), or catalysts in which ultrafine particles of catalyst components are dispersed and supported on a support with a large specific surface area such as zeolites, graphite, activated carbon, or nanocarbons (e.g., vapor-grown carbon fibers, carbon nanotubes, carbon nanohorns, graphene, etc.). Furthermore, as a support component that provides a high co-catalyst effect, materials containing alkali metal and alkaline earth metal amides and imides (e.g., NaNH2, Ca(NH2)2, Mg(NH2)2, CaNH, LiCaN, etc.) may be used as a support or mixed with the above-mentioned support. For the catalyst component ultrafine particles, those having a fine particle size (1 nm or more and less than 1 μm) such as iron (Fe) oxide, nickel (Ni), cobalt (Co), ruthenium (Ru), palladium (Pd), rhodium (Rh), iridium (Ir), and platinum (Pt) are used, and preferably, ultrafine particles of ruthenium (Ru) that can particularly promote the decomposition reaction at low temperatures and lower the decomposition temperature are used. The decomposition temperature when carrying out a decomposition reaction using a catalyst supported with ultrafine particles of ruthenium (Ru) is also affected by the material, composition, structure, etc. of the above-mentioned support, but for ruthenium (Ru) supported catalysts that show excellent performance, it is set to, for example, 500 to 600°C. This makes it easier to decompose ammonia gas at a high decomposition rate (which also depends on the pressure inside the ammonia decomposition unit 9, but for example, about 95-99% at an absolute pressure of 1 MPa or less). In this case, the additional temperature is, for example, above 600°C and below 900°C.

[0055] The catalyst used for ammonia decomposition can be of various forms. To reduce the pressure loss of ammonia gas flowing through the ammonia decomposition unit 9, it may be filled with granulated catalyst, or it may be arranged in a honeycomb shape. The honeycomb-shaped catalyst may be a catalyst carrier on which the aforementioned ultrafine particle catalyst for ammonia decomposition is supported and then molded into a honeycomb shape, or it may be a catalyst carrier on which ultrafine particle catalyst for ammonia decomposition is supported and coated with a nitridation-resistant metal honeycomb (described later).

[0056] The decomposition gas mainly consists of hydrogen gas and nitrogen gas in a molar ratio of 75:25, according to the production ratio in the reaction equation 2NH3 → 3H2 + N2. In addition, at the stage produced in the ammonia decomposition section 9, it also contains a small amount (e.g., 1000 volume ppm to 5 volume%) of undecomposed residual ammonia gas that can poison the electrodes of a polymer electrolyte fuel cell (PEFC).

[0057] The decomposition gas line 11 is connected to the ammonia decomposition unit 9 and is a line that guides the decomposition gas downstream.

[0058] The cooler 13 is installed in the decomposition gas line 11 and is a device for cooling the decomposition gas. By cooling the decomposition gas to, for example, below 100°C, preferably to room temperature (about 25°C) or lower, more residual ammonia gas can be adsorbed onto the adsorbent in the ammonia adsorption section described later, improving the removal rate of residual ammonia gas. Furthermore, by cooling the decomposition gas, more permeate gas containing hydrogen gas can be separated from the residual gas containing nitrogen gas in the hydrogen separation section described later, improving the removal rate of nitrogen gas. In addition, if the hydrogen separation section includes heat-sensitive polymer separation membranes or resin containers, cooling can prevent deterioration of these materials.

[0059] The primary purification section 15 is located downstream of the ammonia decomposition section 9 and is connected to the decomposition gas line 11 downstream of the cooler 13. It removes either residual ammonia gas or nitrogen gas from the cooled decomposition gas to produce primary purified gas, which is then discharged downstream. Furthermore, the secondary purification section 19, located downstream of the primary purification section 15, removes the remaining of the residual ammonia gas and nitrogen gas from the primary purified gas to produce secondary purified gas, which is then discharged downstream. In the following, the case in which residual ammonia gas is removed in the primary purification section 15 and nitrogen gas is removed in the secondary purification section 19 will be explained using hydrogen gas production apparatus A1 as an example.

[0060] The primary purification section 15 of the hydrogen gas production apparatus A1 shown in Figure 1 is an ammonia adsorption section that removes residual ammonia gas. In the following description, the ammonia adsorption section, which is the primary purification section 15, will be referred to as the ammonia adsorption section 15. The ammonia adsorption section 15 has an adsorbent that adsorbs residual ammonia gas. The ammonia adsorption section 15 uses an adsorption tower in which the decomposition gas flows from the inlet side to the outlet side, and the residual ammonia gas is adsorbed onto the adsorbent placed inside.

[0061] The adsorbent used in the ammonia adsorption section 15 is preferably a porous adsorbent having many Lewis acid sites, such as zeolites of type X or type A. In particular, zeolites having many pores with a pore size of 5 to 20 Å, such as zeolite 13X, are well used. These zeolites preferably contain at least one cation from lithium (Li), calcium (Ca), and sodium (Na). These adsorbents can be reused repeatedly because they can be regenerated by desorbing the ammonia gas after reaching breakthrough by adsorbing residual ammonia gas, etc., and then heating. When using adsorbents such as the above-mentioned zeolites, if the decomposition gas contains water as an impurity, not only residual ammonia gas but also water is often adsorbed by the adsorbent and removed from the decomposition gas.

[0062] The primary purified gas is a mixed gas consisting of approximately 75 volume% hydrogen gas and 25 volume% nitrogen gas. Furthermore, the concentration of residual ammonia gas that can poison the electrodes of a polymer electrolyte fuel cell (PEFC) is, for example, several hundred volume ppb or less, preferably less than 100 volume ppb, in the primary purified gas.

[0063] The primary purification gas line 17 is connected to the primary purification unit 15 and is a line that guides the primary purification gas downstream.

[0064] The secondary purification section 19 is located downstream of the primary purification section 15 and is connected to the primary purified gas line 17. It removes the other of residual ammonia gas and nitrogen gas from the primary purified gas to produce secondary purified gas, which is then discharged downstream. The secondary purification section 19 of the hydrogen gas production apparatus A1 shown in Figure 1 is a hydrogen separation section that removes nitrogen gas. In the following description, the hydrogen separation section, which is the secondary purification section 19, will be referred to as the hydrogen separation section 19. The hydrogen separation section 19 has a separation membrane and is configured to separate the decomposed gas or primary purified gas into a permeate gas containing most of the hydrogen gas (more than 50% by volume) that has permeated the separation membrane and a residual gas containing the remainder of the hydrogen gas and nitrogen gas that remain upstream of the separation membrane without permeating it, and then discharge the separated gases. The hydrogen separation unit 19 has an inlet for primary purified gas and an outlet for secondary purified gas (hereinafter referred to as the inlet and outlet, respectively), and a flow-through gas separation membrane module is used in which a separation membrane with a structure that allows permeate gas to pass through from the purified gas and separate it from the residual gas is placed in the middle of the flow path of the purified gas that flows from the inlet to the outlet.

[0065] Gas is injected into the gas separation membrane module from the inlet. Due to the pressure difference between the upstream (inlet) and downstream (outlet) sides of the module, separated by the separation membrane, hydrogen gas selectively permeates the separation membrane from the components of the gas, while nitrogen gas hardly permeates. As a result, a hydrogen-dominant gas (containing a small amount of nitrogen gas that permeates the separation membrane along with the hydrogen gas) is discharged from the downstream (outlet) side. On the other hand, the residual hydrogen gas that does not permeate the separation membrane remains on the upstream (inlet) side of the separation membrane. This nitrogen-dominant gas (residual gas), including the residual hydrogen gas that does not permeate the separation membrane, is discharged from the outlet in the module for discharging non-permeable gas. The ratio of the amount of hydrogen gas permeating through the separation membrane (permeation rate) to the flow rate of hydrogen gas in the primary purified gas introduced into the hydrogen separation unit 19 corresponds to the proportion of hydrogen gas in the primary purified gas that is recovered as secondary purified gas (recovery rate). The hydrogen gas recovery rate is proportional to the amount (rate) of hydrogen gas permeating through the separation membrane.

[0066] Separation membranes used to separate hydrogen gas generally include membranes made of palladium (Pd) or palladium alloys, membranes made of crystalline or amorphous ceramics such as zeolite, porous silica, porous alumina, or porous aluminosilicate, and porous polymer membranes having a separation layer made of aromatic polyamide, aromatic polyimide, or polytetrafluoroethylene (PTFE). Preferably, the separation membrane should have high selective permeability (the ability to allow more hydrogen gas to pass through than nitrogen gas at a given differential pressure) and a high hydrogen gas permeability rate (fast permeation rate).

[0067] Of the separation membranes described above, membranes made of palladium (Pd) or palladium alloy exhibit particularly excellent selective permeability of hydrogen gas, and high-purity hydrogen gas of 99.97% by volume or more, as specified in the international standard ISO 14687-2 2012 Grade D (hereinafter referred to as ISO 14687-2), can be obtained in a single permeation. However, because palladium (Pd) is rare and expensive, it is difficult to manufacture membranes with a large surface area, and problems such as the extremely slow permeation rate of hydrogen gas, especially at room temperature (around 25°C), requiring the application of an extremely large differential pressure. For this reason, it is not suitable for the rapid purification of large quantities of hydrogen gas required for the operation of fuel cell systems and mobile vehicles, which will be described later. Furthermore, in order to separate hydrogen gas using separation membranes made of palladium (Pd) or palladium alloy, it is necessary to heat the decomposition gas to a high temperature upstream of the hydrogen separation unit 19. For this reason, separation membranes made of palladium (Pd) or palladium alloy are excluded from the separation membranes used in the hydrogen separation unit 19.

[0068] On the other hand, separation membranes having separation layers made of crystalline or amorphous ceramics such as zeolite (e.g., SOD-type zeolite), porous silica, porous alumina, or porous aluminosilicate, or porous polymer separation membranes having separation layers made of aromatic polyamide, aromatic polyimide, or polytetrafluoroethylene (PTFE), are less expensive than palladium (Pd) or palladium alloy separation membranes, and have fewer restrictions on raw material resources. These separation membranes have a large number of micropores with pore sizes at the angstrom level (1 angstrom or more, less than 100 nm), and separation based on differences in the molecular size of gas components is possible. Among these micropores, those having a narrow pore size distribution of approximately 3 Å, which corresponds to the intermediate molecular diameters of hydrogen and nitrogen, are particularly preferred. Therefore, as the separation membrane of the hydrogen separation section 19, ceramic separation membranes or polymer separation membranes with the above specifications are preferably used.

[0069] In particular, polymer separation membranes are generally lightweight and can be molded into a variety of shapes (for example, thin, hollow fiber-like structures or wound structures where the separation membrane is wound into a tube). In separation membrane modules in which such hollow fiber-like membranes are bundled and sealed in a container, a separation membrane with a large surface area can be efficiently sealed in the container, increasing the amount of hydrogen gas permeate per unit of module size. This is advantageous for on-site installation in confined spaces or mounting on mobile devices. Furthermore, some polymer separation membranes are surface-treated to increase the selective permeability and permeation rate (permeation velocity) of hydrogen gas. With such polymer separation membranes, a sufficient hydrogen gas permeation velocity can be obtained at room temperature (around 25°C) even under relatively small differential pressure conditions. Therefore, it is not necessary to pressurize the primary purified gas to a high pressure exceeding 1 MPa upstream of the hydrogen separation unit 19, reducing the power required for hydrogen gas production and thus reducing manufacturing costs. For this reason, polymer separation membranes with the above specifications are particularly preferred.

[0070] The magnitude of the differential pressure between the upstream and downstream sides of the separation membrane is set to an appropriate size so that a predetermined hydrogen gas permeation rate and a predetermined recovery rate can be obtained. For example, when performing separation at room temperature (approximately 25°C) using a polymer separation membrane with good performance, the differential pressure is set to a range of, for example, 0.3 to 0.9 MPa, preferably 0.5 to 0.7 MPa.

[0071] Selective permeability and permeability (permeation rate) are generally affected by temperature; as the temperature rises, selective permeability tends to decrease slightly, while permeability (permeation rate) often increases. Therefore, it is preferable that the temperature of the gas introduced into the separation membrane module be determined considering the balance between these two factors. Furthermore, when performing separation using a polymer separation membrane, which generally has lower heat resistance than separation membranes made of ceramics, it is preferable that the hydrogen gas production apparatus A1 can be suitably operated at, for example, around room temperature (approximately 25°C), and that sufficient selective permeability and permeability (permeation rate) of hydrogen gas can be achieved in that temperature range. According to one embodiment, the separation membrane is a polymer or ceramic separation membrane, and the differential pressure is preferably 0.3 to 0.9 MPa. By using a ceramic or polymer separation membrane, a sufficient hydrogen gas permeation rate can be obtained at around room temperature (25°C) even with a relatively small differential pressure of 0.3 MPa to 0.9 MPa, and both selective permeability and permeability of hydrogen gas can be achieved. Therefore, by supplying the separated hydrogen gas to a fuel cell, sufficient power can be secured to propel, for example, a mobile vehicle equipped with a fuel cell.

[0072] The rate of secondary purified gas (meaning hydrogen gas in the following explanation of secondary purified gas permeation rate) per unit time that is separated and permeated by the separation membrane is determined by the permeation area of ​​the separation membrane, the permeation coefficient of the secondary purified gas in the separation membrane, and the magnitude of the differential pressure, as shown in Equation 1 below. Here, the permeation coefficient is the permeation area, differential pressure, and rate of secondary purified gas permeation per unit time that are specific to the separation membrane. Formula 1: (Secondary purification gas permeation rate per unit time in the separation membrane [kg-H2 / h]) =(Permeable area of ​​separation membrane [m²] 2 ]) × (Permeation coefficient of secondary purified gas [kg-H2 / (m 2 (·MPa·h)]) × (Differential pressure [MPa]) From Equation 1, the permeation rate of the secondary purified gas per unit time through the separation membrane is proportional to the permeation area (membrane area) of the separation membrane, the permeation coefficient of the secondary purified gas through the separation membrane, and the differential pressure. Similarly, the hydrogen gas recovery rate is also proportional to these factors. Therefore, for a separation membrane with a predetermined hydrogen gas permeation coefficient, the hydrogen gas recovery rate can be controlled by appropriately setting the membrane area and differential pressure. The permeation rate of the secondary purified gas per unit time in the hydrogen gas production apparatus A1 corresponds to the production rate of the secondary purified gas per unit time. Accordingly, the production rate of the secondary purified gas per unit time is also given by Equation 1.

[0073] To ensure the desired permeation rate (permeation velocity) of the secondary purified gas, a sufficient membrane area is required. Therefore, if a single separation membrane module cannot provide sufficient membrane area, the hydrogen separation unit 19 may consist of multiple separation membrane modules arranged in parallel in the direction of gas flow. Based on the aforementioned Equation 1, the required number of parallel-arranged separation membrane modules (required number of parallel arrangements) can be determined based on the value calculated by the following Equation 2. Note that the decimal part of the calculation result is rounded up. Since the hydrogen gas recovery rate and the permeation rate (permeation velocity) of the secondary purified gas are proportional to each other, the required number of parallel-arranged separation membrane modules in Equation 2 is also the required number of parallel arrangements to obtain a hydrogen gas recovery rate corresponding to the desired permeation rate (permeation velocity). Formula 2: (Required number of parallel connections for the separation membrane module) = (Target secondary purification gas permeation rate per unit time [kg-H2 / h]) / {(Permeable area of ​​the separation membrane per separation membrane module [m²] 2 ]) ×(Permeation area of ​​the separation membrane, differential pressure, and unit time, per unit of the separation membrane specific to the separation membrane module) Secondary purification gas permeation rate [kg-H2 / (m 2 (·MPa·h)]) × (Set differential pressure [MPa])

[0074] The secondary purified gas is produced by the hydrogen gas production unit A1 and discharged from the hydrogen gas production unit A1. The secondary purified gas is a mixed gas (hydrogen-based gas) mainly composed of hydrogen gas, which substantially does not contain residual ammonia gas that could poison the negative electrode when used as fuel gas for a polymer electrolyte fuel cell (PEFC), and most of the nitrogen gas has been removed by the hydrogen separation unit 19. The mixed gas (hydrogen-based gas) used as secondary purified gas consists, for example, of 95-98 volume percent hydrogen gas and 2-5 volume percent nitrogen gas. Therefore, the amount of nitrogen gas contained in the secondary purified gas is significantly less than when nitrogen removal is not performed (nitrogen gas concentration of approximately 25 volume percent). For this reason, when the secondary purified gas is used as fuel gas for a polymer electrolyte fuel cell (PEFC), concentration polarization is suppressed compared to when nitrogen removal is not performed, allowing for the maintenance of high power generation efficiency and making it less likely for the maximum output during power generation to decrease. Furthermore, since the energy density of the secondary purified gas increases compared to when nitrogen removal is not performed, the amount of energy stored when the secondary purified gas is filled into an external tank (for example, a purified gas tank (including a high-pressure hydrogen tank) as described later) is greatly improved.

[0075] ISO 14687-2 specifies the permissible concentrations of various impurities, such as ammonia, that can poison the electrodes of polymer electrolyte fuel cells (PEFCs), and also stipulates that the hydrogen purity must be 99.97% or higher. According to this standard, the permissible concentration of helium is less than 300 ppm by volume, and the permissible concentration of nitrogen and argon combined is less than 100 ppm by volume. However, these trace components only slightly dilute the hydrogen gas concentration and, even if present in the secondary purified gas, have little effect on the characteristics of polymer electrolyte fuel cells (PEFCs). On the other hand, since most of the nitrogen gas contained in the primary purified gas is removed in the secondary purified gas (for example, the hydrogen gas concentration is about 95-98% by volume), the concentration polarization at the negative electrode when the secondary purified gas is used as fuel gas for a polymer electrolyte fuel cell (PEFC) is significantly suppressed compared to when nitrogen removal is not performed (hydrogen gas concentration is about 75% by volume or less). As a result, the power generation efficiency and the magnitude of the maximum output during power generation are not significantly different from when high-purity hydrogen as defined in ISO 14687-2 is used. Therefore, when generating electricity using a polymer electrolyte fuel cell (PEFC) with secondary purified gas as fuel, a special polymer electrolyte fuel cell (PEFC) with grooves in the negative electrode, as described in Non-Patent Literature 3, is not particularly necessary. Furthermore, the energy density when filled under high pressure in an external tank, and the fluid properties, such as the flow resistance at room temperature (about 25°C) generated by the flow of the secondary purified gas, are not significantly different from high-purity hydrogen gas that meets the above standards.

[0076] The secondary purification gas line 21 is connected to the secondary purification unit 19 (hydrogen separation unit) and is a line that guides the secondary purification gas downstream and discharges it from the hydrogen gas production device A1. The discharged secondary purification gas may be supplied directly to a destination (for example, a fuel cell or high-pressure hydrogen tank, which will be described later), or it may be stored in the purification gas tank of the hydrogen gas supply device, which will be described later.

[0077] Liquefied ammonia, ammonia gas, decomposition gas, primary purified gas, and secondary purified gas (hereinafter, these gases may be collectively referred to as a series of gases) are configured to flow downstream through the raw ammonia line 3, decomposition gas line 11, primary purified gas line 17, and secondary purified gas line 21, respectively, due to the pressure difference between the vapor pressure of ammonia in tank 1 and the pressure on the downstream side of the separation membrane (upstream side of the vacuum pump 22), which is reduced by the vacuum pump 22 located downstream of the separation membrane and which depressurizes and exhausts the secondary purified gas. The differential pressure that drives hydrogen separation by the separation membrane is formed as a pressure drop between the upstream and downstream sides of the separation membrane caused by the depressurized exhaust by the vacuum pump 22. In other words, the differential pressure is formed as part of the aforementioned pressure difference. Here, the pressure on the upstream side of the separation membrane means the gas pressure downstream of the point on the primary purified gas line 17, which is connected to the hydrogen separation unit 19 upstream of the hydrogen separation unit 19 (in the example shown in Figure 1, the upstream pressure regulator 18, which will be described later). Furthermore, the downstream side of the separation membrane refers to the gas pressure upstream of the point closest to the hydrogen separation unit 19 (the downstream pressure regulator 20 in the example shown in Figure 1) on the secondary purification gas line 21 connected to the hydrogen separation unit 19, downstream of the hydrogen separation unit 19.

[0078] The differential pressure required to separate and permeate hydrogen in the separation membrane is directly adjusted by adjusting or driving the upstream pressure regulator 18, the pressure reducer 22, and the downstream pressure regulator 20.

[0079] The upstream pressure regulator 18 is a device that adjusts the pressure upstream of the hydrogen separation unit 19 to an appropriate pressure by adjusting the opening of the flow path between the ammonia adsorption unit 15 and the hydrogen separation unit 19. A general pressure regulating valve (pressure reducing valve) can be used for the upstream pressure regulator 18, but it is more preferable that it also has a function to detect the mass flow rate of the gas before hydrogen separation flowing through the upstream pressure regulator 18.

[0080] The vacuum pump 22 is a device that reduces the pressure upstream of the vacuum pump 22 (downstream of the hydrogen separation unit 19) by drawing in the secondary purified gas containing hydrogen gas that has permeated through the separation membrane in the hydrogen separation unit 19 and discharging it downstream. For example, a pump is used for the vacuum pump 22. By reducing the pressure upstream of the vacuum pump 22, a reduced pressure state is created downstream of the separation membrane, which generates the differential pressure as part of the above pressure difference. In this way, the differential pressure is created using the vacuum pump 22 which creates the above pressure difference so that liquefied ammonia, ammonia gas, decomposition gas, primary purified gas, and secondary purified gas flow downstream from the tank 1 to the secondary purified gas line 21. Therefore, there is no need to separately place a vacuum pump or other vacuum pump downstream of the separation membrane to create the above differential pressure. In other words, in the hydrogen gas production apparatus A1, the vacuum pump for creating the above pressure difference and the vacuum pump for creating the above differential pressure are shared by the vacuum pump 22.

[0081] The downstream pressure regulator 20 is a device that adjusts the opening of the flow path between the hydrogen separation unit 19 and the pressure reducer 22, thereby mitigating the reduced pressure state created by the pressure reducer 22 and appropriately adjusting the pressure downstream of the hydrogen separation unit 19 to control the flow rate of the secondary purified gas permeating the separation membrane to a predetermined flow rate. Similar to the upstream pressure regulator 18, a general pressure regulating valve (pressure reducing valve) can be used for the downstream pressure regulator 20, but it is more preferable that it also has a function to detect the mass flow rate of the secondary purified gas flowing through the downstream pressure regulator 20. By controlling the flow rate of the secondary purified gas so that the detected mass flow rate becomes the desired mass flow rate, the differential pressure across the separation membrane in the hydrogen separation unit 19 is appropriately adjusted, and the secondary purified gas containing hydrogen gas that has permeated the separation membrane at a flow rate determined based on that differential pressure is discharged through the secondary purified gas line 21 by the pressure reducer 22.

[0082] The hydrogen gas production apparatus A1 is further equipped with a residual gas discharge line 23. The residual gas discharge line 23 is a line for discharging to the outside the remaining portion of the primary purified gas, which is the nitrogen-based gas (nitrogen-dominant gas or residual gas) that has been separated from the permeate gas containing most of the hydrogen gas by the hydrogen separation unit 19. In the following description, the nitrogen-dominant gas or residual gas will be simply referred to as "nitrogen gas". The residual gas discharge line 23 is connected to the residual gas outlet provided in the hydrogen separation unit 19 so that the residual gas is discharged to the outside of the hydrogen separation unit 19. A nitrogen discharge pressure regulator 24 is provided in the residual gas discharge line 23. The nitrogen discharge pressure regulator 24 adjusts the opening of the flow path of the residual gas discharge line 23 to maintain the pressure at the outlet of the residual gas of the hydrogen separation unit 19 at a pressure slightly lower than the pressure at the inlet of the primary purified gas before hydrogen separation into the hydrogen separation unit 19, which is regulated by the upstream pressure regulator 18. It also adjusts the flow rate of the residual gas flowing through the residual gas discharge line 23 to the flow rate obtained by subtracting the flow rate of the secondary purified gas flowing through the downstream pressure regulator 20 from the flow rate of the primary purified gas before hydrogen separation flowing through the upstream pressure regulator 18. While a general pressure regulating valve (pressure reducing valve) can be used for the nitrogen discharge pressure regulator 24, it is more preferable to have a function that detects the mass flow rate of the residual gas flowing through the nitrogen discharge pressure regulator 24 and controls the flow rate of the residual gas so that the detected mass flow rate is equal to the value obtained by subtracting the mass flow rate of the secondary purified gas flowing through the downstream pressure regulator 20 from the mass flow rate of the primary purified gas before hydrogen separation flowing through the upstream pressure regulator 18. The nitrogen discharge pressure regulator 24 causes the residual gas to be continuously discharged from the hydrogen separation unit 19 through the residual gas discharge line 23.

[0083] In the hydrogen gas production apparatus A1, the pressure difference between the internal pressure (vapor pressure) of tank 1 and the pressure upstream of the vacuum pump 22, formed by the reduced-pressure exhaust of the vacuum pump 22, is used as the driving force for the flow of liquefied ammonia and a series of gases downstream. The gas flowing downstream is formed when ammonia gas generated in the raw ammonia line 3 downstream of the vaporizer 5 is transformed into decomposed gas in the ammonia decomposition section 9, then into primary purified gas in the primary purification section 15 (ammonia adsorption section 15 in this case), and finally into secondary purified gas in the secondary purification section (hydrogen separation section 19 in this case). Through this process in which the gases are sequentially transformed, the internal pressure (vapor pressure) of tank 1 must be maintained at a predetermined supply pressure so that liquefied ammonia and a series of gases flow downstream from tank 1 to the secondary purified gas line 21 without stagnation. Furthermore, the aforementioned pressure difference is adjusted by the upstream pressure regulator 18 and the downstream pressure regulator 20. This enables a series of gas flows from tank 1 downstream, allowing for the production of secondary purified gas at a predetermined rate per unit time using the separation membrane.

[0084] During operation of the hydrogen gas production apparatus A1, as liquefied ammonia flows downstream from tank 1, changes occur such as vaporization of liquefied ammonia, an increase in gas volume due to the heating and decomposition of ammonia gas, and a decrease in gas volume due to cooling in cooler 13. Even with these changes, it is preferable that the internal pressure (vapor pressure) of tank 1, the depressurization and exhaust capacity of the depressurizer 22, the processing capacity (processing amount per unit time) and flow resistance (pressure loss) of each piece of equipment within the hydrogen gas production apparatus A1, and the flow resistance (pressure loss) of each gas line are appropriately designed and controlled so that the gas pressure decreases sequentially as it moves downstream without stagnation or backflow of these gases within the hydrogen gas production apparatus A1.

[0085] In hydrogen gas production apparatus A1, the pressure difference between the internal pressure (vapor pressure) of tank 1 and the pressure downstream of the separation membrane, which has been reduced by the pressure reducer 22, is used to create the differential pressure. This allows for the separation of hydrogen gas using the separation membrane, thus eliminating the need for high-pressure compressors (e.g., those that pressurize at 1 MPa or more) commonly used for hydrogen gas separation by pressure swing (PSA) or cryogenic separation methods. Furthermore, it eliminates the need to frequently start and keep running a high-pressure compressor, as is required in the PSA method. Additionally, it eliminates the need for cooling under even higher pressure conditions or using adiabatic expansion from a high-pressure state, as is required in cryogenic separation methods. Therefore, hydrogen gas production apparatus A1 reduces the power consumed to increase the pressure upstream of the separation membrane, thereby reducing the energy consumed in hydrogen gas production. Moreover, while high-pressure compressors required for PSA and cryogenic separation methods are large, hydrogen gas production apparatus A1 does not require them, thus saving installation space and allowing for a smaller and simpler hydrogen gas production apparatus A1. In addition, as mentioned above, in the hydrogen gas production apparatus A1, the ammonia gas is heated by the first electric heater 7a during the startup period, which increases the ammonia decomposition rate at an early stage and improves the productivity of hydrogen gas. In other words, with the hydrogen gas production apparatus A1, when producing hydrogen gas using ammonia as a raw material, the ammonia can be efficiently decomposed during startup, and nitrogen gas can be removed (hydrogen gas separated) without using a high-pressure compressor, etc., which reduces the power consumed and makes the hydrogen gas production apparatus A1 compact and simple.

[0086] Because of its compact size, the hydrogen gas production device A1 can be mounted on mobile vehicles such as fuel cell vehicles (FCVs) and fuel cell (FC) ships. Since hydrogen gas can be continuously separated using a separation membrane, the hydrogen gas production device A1 is suitable for, for example, continuously supplying fuel gas to polymer electrolyte fuel cells (PEFCs).

[0087] Furthermore, the hydrogen gas production apparatus A1 may also be equipped with a pressurizer 17a for pressurizing the primary purified gas, as shown in parentheses on the primary purified gas line 17 in Figure 1. The pressurizer 17a pressurizes the primary purified gas to, for example, 0.1 to 0.5 MPa. For example, a pump or a compressor can be used for the pressurizer 17a.

[0088] In this case, the internal pressure (vapor pressure) of tank 1 is maintained at a predetermined supply pressure so that liquefied ammonia and a series of gases can flow downstream from tank 1 to the secondary purification gas line 21 without stagnation. This enables the flow of liquefied ammonia and each of the gases downstream of tank 1, allowing the secondary purification gas to permeate the separation membrane at a predetermined rate per unit time and produce hydrogen gas. In other words, by providing the pressurizer 17a, the internal pressure (vapor pressure) of tank 1 can be reduced by the amount of pressurization by the pressurizer 17a (for example, 0.1 to 0.5 MPa) compared to when the pressurizer 17a is not provided. As a result, the pressure in the ammonia decomposition section 9 downstream of tank 1 is also reduced by the amount of pressurization by the pressurizer 17a compared to when the pressurizer 17a is not provided. The ammonia decomposition reaction (2NH3 → 3H2 + N2) in the ammonia decomposition section 9 is a reaction in which the gas volume increases as it progresses. Therefore, under certain decomposition temperature conditions, the lower the pressure, the higher the ammonia decomposition rate, producing more hydrogen gas and reducing the amount of residual ammonia gas. Therefore, by providing the pressurizer 17a, the pressure in the ammonia decomposition section 9 can be reduced. As a result, the ammonia decomposition rate in the ammonia decomposition section 9 can be improved. Furthermore, by providing the pressurizer 17a, even if the internal pressure (vapor pressure) of the tank 1 unexpectedly drops due to a rapid decrease in the external ambient temperature, and the differential pressure required for hydrogen separation at the separation membrane becomes insufficient, the insufficient pressure can be compensated for by pressurizing with the pressurizer 17a, thereby maintaining the processing capacity of the membrane separation. Note that the above parenthetical notes in Figure 1 indicate that they are optional components, and in the hydrogen gas production apparatus A1, whether or not to provide the pressurizer 17a can be selected after considering the advantages and disadvantages described above.

[0089] According to one embodiment, it is preferable that the heating section 8, as a heating element 7, includes a first electric heater 7a, a combustor 29, and a first heat exchange heater 7c. It is also preferable that the heating section 8 further includes a combustion gas line 31 as part of the heating element 7. The combustion gas line 31 is connected to the combustor 29 and is a line through which combustion gas flows.

[0090] The combustor 29 is a device that burns the residual gas discharged from the hydrogen separation unit 19 together with air and discharges the combustion gas. The residual gas is led to the combustor 29 through the residual gas discharge line 23. The combustor 29 is connected to an outside air intake line 32 that introduces air from the outside. By mixing the residual gas with air at an appropriate flow rate ratio, as described later, the composition of the mixed gas can be brought within the combustion range, and it can be burned together with the air. Preferably, the amount of air introduced from the outside is such that the amount of oxygen in the air is equal to or greater than the stoichiometric ratio of hydrogen gas in the residual gas introduced into the combustor 29. By supplying a sufficient amount of oxygen necessary for combustion, incomplete combustion of the residual gas can be suppressed.

[0091] The first heat exchange heater 7c is a heater for the first heat exchanger 33 that heats the ammonia gas by heat exchange with the combustion gas discharged from the combustor 29. The first heat exchanger 33 is a device composed of a part of the combustion gas line 31 which forms the first high-temperature side flow path through which the combustion gas flows, and the first heat exchange heater 7c which forms the first low-temperature side flow path through which the ammonia gas flows. The first heat exchanger 33 is configured such that the combustion gas is cooled and the ammonia gas is heated by heat exchange between the combustion gas flowing through the first high-temperature side flow path and the ammonia gas flowing through the first low-temperature side flow path. Since the combustion gas is obtained using gas produced in the hydrogen gas production device A as fuel, the heat source necessary for heating the ammonia gas can be procured within the hydrogen gas production device A.

[0092] It is preferable that the heating of the ammonia gas by the first heat exchange heater 7c is performed after the start of the steady-state operation period, which begins when a permeate gas exceeding a predetermined flow rate is discharged from the hydrogen separation unit 19. This allows the heat source necessary for raising the temperature of the ammonia gas for the majority of the operating period of the hydrogen gas production apparatus A to be procured within the hydrogen gas production apparatus A, and the ammonia gas can be raised to the decomposition temperature without inputting external energy. For this reason, it is preferable that the heating of the ammonia gas by the first heat exchange heater 7c is performed continuously throughout the steady-state operation period of the hydrogen gas production apparatus A. The steady-state operation period is preferably started when the flow rate of the permeate gas stabilizes (for example, after 5 minutes, it remains within the set flow rate range exceeding a predetermined flow rate), and at least the temperature of the ammonia decomposition catalyst in the ammonia decomposition unit 9, or the temperature of the apparatus of the ammonia decomposition unit 9 (for example, the decomposition tower), stabilizes (for example, after 5 minutes, they each remain within the predetermined temperature range). The flow rate and temperature of the permeate gas discharged from the hydrogen separation unit 19 are measured, for example, by a flow meter and a thermometer installed in the residual gas discharge line 23. The temperature of the ammonia decomposition catalyst and the ammonia decomposition unit 9 is measured, for example, by a thermometer attached to the ammonia decomposition catalyst and the ammonia decomposition unit 9.

[0093] In this embodiment, it is preferable that the output of the first electric heater 7a be continuously or gradually reduced after the start of the steady-state operation period. This allows for stable heating of the ammonia gas to the decomposition temperature during operation of the hydrogen gas production apparatus A while suppressing power consumption by the first electric heater 7a and reducing the amount of external energy input. On the other hand, it is preferable that the heating of the ammonia gas by the first heat exchange heater 7c be performed as the flow rate of the combustion gas gradually increases during the start-up period. This allows for stabilizing the amount of heat source required to raise the ammonia gas to the decomposition temperature while gradually replacing the heating by the first electric heater 7a with the heating by the first heat exchange heater 7c. On the other hand, it is also preferable that the output of the first electric heater 7a be set to zero at the start of the steady-state operation period, as this also reduces the amount of external energy input.

[0094] Furthermore, the residual gas discharged from the hydrogen separation unit 19 contains hydrogen gas, and unless the hydrogen gas recovery rate in the separation membrane is significantly high (for example, 95% by volume or more), there is a risk of combustion, and it is often not possible to release it directly into the atmosphere. Moreover, the hydrogen gas recovery rate can be increased by significantly increasing the area and differential pressure of the separation membrane, which is costly. According to this embodiment, the residual gas can be safely treated by combustion, while the ammonia gas is heated and used as a heat source to advance the ammonia decomposition reaction in the ammonia decomposition unit 9.

[0095] Preferably, the heating unit 8 for raising the temperature further includes a second electric heater 7b that uses electricity to adjust the temperature of the ammonia gas flowing through the ammonia decomposition unit 9. During steady-state operation, the temperature of the ammonia gas introduced into the ammonia decomposition unit 9 may fall below or fluctuate below the decomposition temperature due to insufficient or fluctuating temperature and flow rate of the combustion gas supplied to the first heat exchanger 33. Also, the temperature of the ammonia gas introduced into the ammonia decomposition unit 9 may decrease as the ammonia decomposition, which is an endothermic reaction, progresses, and may fall below the decomposition temperature. In order to suppress insufficient or fluctuating temperature and flow rate of the combustion gas supplied to the first heat exchanger 33, it is necessary to adjust the differential pressure between the upstream and downstream sides of the separation membrane to control the flow rate of residual gas introduced into the combustor 29, or to adjust the flow rate of air introduced into the combustor 29 along with the residual gas to adjust the proportion of air in the gas being burned. In order to maintain the temperature of the ammonia gas flowing through the ammonia decomposition unit 9 at the decomposition temperature through these indirect measures, these adjustments must be performed with precision, and it takes a considerable amount of time for the adjustments to be reflected in the temperature of the ammonia gas. Therefore, it is difficult to accurately maintain the temperature of the ammonia gas within the decomposition temperature range using these methods. Since the second electric heater 7b can be heated by energizing it, it can adjust the ammonia gas to the decomposition temperature quickly and accurately (easily), independently of the heating by the first heat exchanger 33.

[0096] The output of the second electric heater 7b is turned on, for example, when the temperature of the ammonia gas flowing through the ammonia decomposition unit 9 falls below the decomposition temperature, and turned off when the temperature of the ammonia gas flowing through the ammonia decomposition unit 9 exceeds the decomposition temperature, so heating by the second electric heater 7b is performed intermittently. When the temperature of the ammonia gas flowing through the ammonia decomposition unit 9 falls below the decomposition temperature, the decomposition rate of ammonia decreases, and the concentration of undecomposed residual ammonia gas in the decomposition gas increases. On the other hand, when the temperature of the ammonia gas flowing through the ammonia decomposition unit 9 exceeds the decomposition temperature, the temperature inside the ammonia decomposition unit 9 becomes too high, which may lead to nitrogen embrittlement of the metal materials constituting the ammonia decomposition unit 9 due to ammonia.

[0097] It is preferable that the heating of the ammonia gas by the second electric heater 7b is performed after the heating of the ammonia gas by the first electric heater 7a is stopped during the steady-state operation period. As described above, insufficient or fluctuating temperature and flow rate of the ammonia gas in the ammonia decomposition unit 9 is likely to occur during the steady-state operation period, after the heating by the first electric heater 7a is replaced by the heating by the first heat exchanger 33, due to insufficient or fluctuating temperature and flow rate of the combustion gas supplied to the first heat exchanger 33. By performing heating by the second electric heater 7b after stopping the heating by the first electric heater 7a, it is possible to suppress insufficient or fluctuating temperature and flow rate of the ammonia gas in the ammonia decomposition unit 9 while suppressing power consumption. On the other hand, heating by the second electric heater 7b may be started during the startup period and performed in parallel with heating by the first electric heater 7a. In this case, the second electric heater 7b performs heating in a manner that assists the heating by the first electric heater 7a.

[0098] According to one embodiment, the heating unit 8 for raising the temperature preferably further includes a second heat exchange heater 5b that vaporizes liquefied ammonia by heat exchange with decomposition gas, and a third electric heater 5a that heats the liquefied ammonia using electric power. In this case, the first electric heater 7a preferably heats the gas obtained by vaporizing liquefied ammonia as ammonia gas.

[0099] The second heat exchange heater 5b is a heater that constitutes the second heat exchanger 25 and functions as a vaporizer 5. The vaporizer 5 and the aforementioned cooler 13 constitute the second heat exchanger 25. The second heat exchanger 25 is a device composed of a cooler 13 which forms a second high-temperature side flow path through which the decomposition gas flows, and a second heat exchange heater 5b which forms a second low-temperature side flow path through which liquefied ammonia flows. The second heat exchanger 25 is configured such that the decomposition gas is cooled and the liquefied ammonia is heated and vaporized by heat exchange between the decomposition gas flowing through the second high-temperature side flow path and the liquefied ammonia flowing through the second low-temperature side flow path. According to this embodiment, the heat source necessary for vaporizing liquefied ammonia is procured within the hydrogen gas production apparatus A, and the heat of the high-temperature decomposition gas can be effectively utilized, thus improving the energy efficiency when producing hydrogen gas. On the other hand, the third electric heater 5a can be heated by energizing, so it can heat the liquefied ammonia quickly and easily, independently of the second heat exchanger 25. Furthermore, heating by the third electric heater 5a provides a stable and easily adjustable heat output, making it easier to avoid uneven vaporization and bumping of liquefied ammonia compared to heating by the second heat exchange heater 5b.

[0100] In this embodiment, the heating unit 8 for raising the temperature preferably heats the liquefied ammonia with the third electric heater 5a during the period from the start of operation of the hydrogen gas production apparatus A until a decomposition gas exceeding a predetermined flow rate is discharged from the ammonia decomposition unit 9 (hereinafter also referred to as the start-up period), preferably during the start-up period. During these periods, the decomposition gas that serves as the heat source for the second heat exchanger 25 has not yet been generated, or if it has been generated, the amount is small, so it is not possible to vaporize the liquefied ammonia using the second heat exchanger 25. Therefore, if only the decomposition gas is used as the heat source, the liquefied ammonia is difficult to vaporize, and even if it is vaporized, the section of the flow path required to raise the temperature of the ammonia gas becomes short, making it difficult to accurately raise the temperature of the ammonia gas to the decomposition gas. By heating with the third electric heater 5a during such a period, the liquefied ammonia can be vaporized quickly and easily, and the next step, raising the temperature of the ammonia, can be performed promptly.

[0101] Furthermore, in this embodiment, it is preferable to heat the liquefied ammonia with the second heat exchange heater 5b during the period that begins when a decomposition gas exceeding a predetermined flow rate is discharged from the ammonia decomposition unit 9 (hereinafter also referred to as the steady-state operation period'), preferably during the steady-state operation period. This allows the hydrogen gas production device A to procure the heat source necessary for vaporizing liquefied ammonia for the majority of the operating period of the hydrogen gas production device A, and to vaporize the liquefied ammonia without inputting external energy. Therefore, it is preferable that the vaporization of liquefied ammonia by the second heat exchange heater 5b is carried out continuously during these periods of the hydrogen gas production device A. The flow rate and temperature of the decomposition gas discharged from the ammonia decomposition unit 9 are measured, for example, by a flow meter and a thermometer installed in the decomposition gas line 11.

[0102] Furthermore, in this embodiment, it is preferable that the output of the third electric heater 5a be continuously or gradually reduced during the steady-state operation period' or after the start of the steady-state operation period. This allows for stable vaporization of liquefied ammonia during the operation of the hydrogen gas production apparatus A while suppressing power consumption by the third electric heater 5a and reducing the amount of external energy input. On the other hand, it is preferable that the vaporization of liquefied ammonia by the second heat exchange heater 5b be performed as the flow rate of the decomposition gas gradually increases during the start-up period' or the start-up period. This allows for a smooth replacement of heating by the third electric heater 5a with heating by the second heat exchange heater 5b while stabilizing the amount of heat source required for vaporization of liquefied ammonia. On the other hand, it is also preferable that the output of the third electric heater 5a be set to zero at the start of the steady-state operation period' or the start of the steady-state operation period, as this also reduces the amount of external energy input.

[0103] The heating of the heating section 8 for temperature rise described above by the electric heaters 7a, 7b, and 5a is preferably performed by controlling the electric heaters 7a, 7b, and 5a with a control device (not shown) provided in the hydrogen gas production apparatus A. The control device is connected to each of the various devices described later, including the electric heaters 7a, 7b, and 5a, and measuring instruments such as flow meters and thermometers, and controls these various devices. The control device may have, for example, one or more analog circuits, digital processing circuits, or a combination thereof. Each digital processing circuit may be, for example, a hardware processor such as an ASIC or FPGA. The control device 101 may also have one or more memory circuits such as RAM. The control device controls the various devices by, for example, having the processing circuit read and execute a control program stored in the memory circuit. The control device determines, for example, whether the system has transitioned from the startup period to the steady-state operation period based on information from measuring instruments regarding the flow rate and temperature of the permeate gas and decomposition gas, and controls the output of the electric heaters 7a and 5a according to the determined period. Furthermore, the control device controls the output of the electric heater 7b based on, for example, information from a measuring instrument regarding the temperature of the ammonia gas flowing through the ammonia decomposition unit 9.

[0104] According to one embodiment, when the heating unit 8 for raising the temperature further includes a combustor 29 and a first heat exchange heater 7c as a heating heater 7, it is preferable that the combustor 29 combusts at least one of a portion of the ammonia gas taken out upstream of the ammonia decomposition unit 9 and a portion of the decomposition gas or purified gas (hereinafter also referred to as off-gas) taken out either downstream of the ammonia decomposition unit 9 together with the residual gas. The off-gas may be taken out directly from the ammonia decomposition unit 9, or it may be taken out downstream of the ammonia decomposition unit 9 from a position on the line, for example, upstream or downstream of the second heat exchanger 25, downstream of the ammonia adsorption unit 15, or downstream of the hydrogen separation unit 19. In the example shown in Figure 2, the off-gas is taken from a portion of the decomposition gas line 11, branches off from the portion of the decomposition gas line 11 downstream of the cooler 13, and flows through a branch gas line 30 that merges with the residual gas discharge line 23, then merges with the residual gas flowing in the residual gas discharge line 23 and is led to the combustor 29. Figure 2 shows a hydrogen gas production apparatus A2 of one embodiment. The branch gas line 30 is a line that connects the portion of the ammonia decomposition unit 9 or line from which the off-gas is taken off to the combustor 29. Since the off-gas contains highly combustible hydrogen gas, it can be burned together with air. On the other hand, the ammonia gas is led to the combustor 29 through a branch ammonia line 3a that branches off from the raw material ammonia line 3 downstream of the second heat exchanger 25. An outside air introduction line 32 is connected to the combustor 29 to introduce air from the outside. Since the ammonia gas is introduced into the combustor 29 together with the highly combustible hydrogen gas contained in the residual gas discharged from the hydrogen separation unit 19, it can be burned together with air.

[0105] According to this embodiment, even if the combustion gas of the residual gas alone is insufficient to meet the heat required for heating and decomposing the ammonia gas, and for compensating for heat loss due to the temperature drop associated with the endothermic reaction, the heat from either a portion of the ammonia gas or the combustion gas of the off-gas is added, thus compensating for the deficiency. It is preferable that the combustion of the residual gas, ammonia gas, and off-gas by the combustor 29 is carried out continuously during the steady-state operation period of the hydrogen gas production device A. It is preferable that the amount of air introduced from the outside is such that the amount of oxygen in the air is equal to or greater than the stoichiometric ratio of the combustion reaction relative to the amount of residual gas, ammonia gas, and off-gas introduced into the combustor 29. By supplying a sufficient amount of oxygen necessary for combustion, incomplete combustion of the residual gas, ammonia gas, and off-gas can be suppressed.

[0106] Furthermore, in this embodiment, a combustion oxidation catalyst to promote the combustion of ammonia gas may be provided on the upstream side inside the combustor 29. By providing a combustion oxidation catalyst inside the combustor 29, the decomposition gas can be efficiently burned even when the hydrogen gas concentration in the decomposition gas is low and the ammonia gas concentration is high at the start of the hydrogen gas production apparatus A, and the ammonia gas can be heated and raised in the first heat exchanger 33. For combustion oxidation catalysts, porous ceramics formed from granulation or honeycomb structures, or honeycomb structures of nitride-resistant metals (for example, nickel (Ni), and nickel alloys such as Inconel® 600, 625, 718, and 750, Incoloy® 800 and 825, Hastelloy® C276 and C22, Nimonic® 75, 80A, and 90, and stainless steel such as SUS310S) can be used, on which ultrafine catalyst particles consisting of at least one of precious metals such as platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), and iridium (Ir), and metal oxides such as manganese (Mn), cobalt (Co), chromium (Cr), and copper (Cu) can be supported.

[0107] Combustion gases may contain nitrogen gas mixed with ammonia gas and decomposition gases, as well as nitrogen oxides (NOx) generated from nitrogen gas in the air. For this reason, a denitrification device (not shown) may be provided in the combustor 29 to remove NOx using a catalyst that decomposes NOx, by methods such as ternary catalytic decomposition or selective catalytic reduction (SCR). This allows denitrification to be performed in parallel with the combustion of the off-gas. When denitrification is performed by the SCR method, ammonia contained in gases such as ammonia gas and decomposition gases acts as a reducing agent that selectively reduces NOx into harmless nitrogen gas and water vapor. Therefore, if the amount of ammonia is insufficient relative to the amount of NOx in the combustion gas, ammonia gas can be additionally supplied to the denitrification device in the combustor 29 through the branched ammonia line 3a (see Figures 2 and 3) and used.

[0108] According to one embodiment, it is preferable that the residual gas discharged from the hydrogen separation unit 19 is led to the combustor 29 without passing through the ammonia adsorption unit 15. If the residual gas passes through the ammonia adsorption unit 15, the hydrogen gas in the residual gas will be mixed with the residual ammonia gas that has been detached from the adsorbent during the regeneration of the adsorbent. This makes it difficult to measure the concentration of residual ammonia gas using a general-purpose measuring instrument, and makes it difficult to confirm that residual ammonia gas has been detached from the adsorbent. Also, according to one embodiment, it is preferable that the residual gas discharged from the hydrogen separation unit 19 is led to the combustor 29 without being heated.

[0109] When the heating unit 8 for temperature increase has a combustor 29 and a first heat exchange heater 7c as the heating heater 7, all of the residual gas discharged from the hydrogen separation unit 19 is used to generate combustion gas, and the combustion gas is cooled and the ammonia gas is heated by heat exchange between the combustion gas and ammonia gas in the first heat exchanger 33. At this time, by appropriately setting the hydrogen gas recovery rate, which is determined by the amount of secondary purified gas permeate per unit time through the separation membrane, the amount of heat from the combustion gas can be balanced with the amount of heat required for heating and decomposing the ammonia gas and compensating for heat loss due to the temperature drop associated with the endothermic reaction. The hydrogen gas recovery rate depends on the magnitude of the heat loss, but for example, 70 to 80 volume percent is used as a guideline, and in many cases, the amount of heat required can be covered by the combustion gas produced by burning the hydrogen gas in the residual gas that is not recovered (20 to 30 volume percent). Therefore, according to one embodiment, it is preferable that the permeate gas from the hydrogen separation unit 19 contains 70 to 80 volume percent of the hydrogen gas in the primary purified gas. In this case, the concentration of hydrogen gas in the residual gas is affected by the hydrogen separation performance of the separation membrane, but it is preferably 30 to 50 volume percent.

[0110] According to one embodiment, it is preferable that the tank 1 has a heat-insulating heater 1a, as shown in Figure 3. Figure 3 is a diagram of a hydrogen gas production apparatus A3 according to one embodiment. The heat-insulating heater 1a is a device that maintains the vapor pressure so as to ensure the downstream flow of liquefied ammonia and a series of gases from the tank 1 to the secondary purified gas line 21 by heating the inside of the tank 1. Specifically, the heat-insulating heater 1a is a device that heats and maintains the temperature inside the tank 1 to a predetermined temperature so as to maintain the tank internal pressure (vapor pressure) at the supply pressure when producing secondary purified gas at a predetermined production rate per unit time, both when a pressurizer 17a is not provided and when one is provided. As described above, this supply pressure is the pressure at which liquefied ammonia and a series of gases flow downstream from the tank 1 to the secondary purified gas line 21 without stagnation. The heat-insulating heater 1a increases the vapor pressure of liquefied ammonia in tank 1, heating and maintaining the tank 1 to a temperature where the internal pressure becomes the supply pressure. This enables the flow of liquefied ammonia and a series of gases downstream of tank 1, allowing for the production of secondary purified gas at a predetermined rate per unit time through the separation membrane. Furthermore, by providing the heat-insulating heater 1a, even if there is a sudden drop in the external ambient temperature, the temperature of tank 1 can be controlled to remain constant, stabilizing the internal pressure (vapor pressure). Even if the differential pressure required for hydrogen separation at the separation membrane is insufficient, the pressure deficiency can be compensated for by heating the inside of tank 1, thus maintaining the membrane separation rate. By suppressing fluctuations in the tank internal pressure in this way, the processing rate of liquefied ammonia per unit time, and furthermore, the production rate of secondary purified gas, can be stabilized.

[0111] In the hydrogen gas production apparatus A3 shown in Figure 3, if the pressurizer 17a is not provided and the hydrogen gas production apparatus is operated using only the pressure reduced by the depressurizer 22 as the pressure that forms the above pressure difference together with the tank internal pressure, it is preferable that the temperature inside the tank 1 be maintained at, for example, 40 to 50°C by the heat-insulating heater 1a so that the tank internal pressure is maintained at the above supply pressure. By maintaining the temperature inside the tank 1 at a temperature slightly higher than the normal ambient temperature in this way, the internal pressure of the tank 1 is maintained at, for example, 1.6 to 2 MPa, and as a result, the internal pressure in the downstream ammonia decomposition section 9 becomes, for example, 1.1 to 1.5 MPa (both are absolute pressures. In the following explanation, unless otherwise specified, pressure refers to absolute pressure when describing the degree of pressurization, depressurization, or the magnitude of the differential pressure). Furthermore, a differential pressure (for example, about 0.5 to 0.9 MPa) required for separating a predetermined amount of hydrogen per unit time can be applied to the separation membrane of the downstream hydrogen separation section 19.

[0112] On the other hand, in the hydrogen gas production apparatus A3 shown in Figure 3, if a pressurizer 17a is also provided in addition to the vacuum pump 22, as described above, the internal pressure (vapor pressure) of the tank 1 can be reduced compared to the case where the pressurizer 17a is not provided, and the pressure in the ammonia decomposition section 9 is also reduced. As a result, the ammonia decomposition rate in the ammonia decomposition section 9 is improved, more hydrogen gas is produced, and the amount of residual ammonia gas can be reduced. At that time, the inside of the tank 1 is heated and maintained by the heat-insulating heater 1a so that the internal pressure (vapor pressure) of the tank 1 is maintained at the supply pressure.

[0113] When the pressurizer 17a described above is installed, it is preferable to maintain the temperature inside the tank 1 at 35-40°C so that the internal pressure of the tank is maintained at the supply pressure. By maintaining the temperature inside the tank 1 at a temperature slightly higher than the normal ambient temperature in this way, the internal pressure of the tank 1 is maintained at, for example, 1.4-1.6 MPa. As a result, the pressure in the downstream ammonia decomposition section 9 is also reduced to, for example, 0.9-1.1 MPa, so that the decomposition rate of the ammonia decomposition reaction can be kept high, for example, 97-99%, especially when a high-performance decomposition catalyst is used. Furthermore, the differential pressure required for hydrogen separation of a predetermined amount per unit time (for example, 0.5-0.9 MPa) can also be applied to the downstream separation membrane. Note that if the pressurizer 17a is not installed as described above and the heating temperature inside the tank 1 is set to about 40-50°C, the pressure in the ammonia decomposition section 9 will be, for example, about 1.1-1.5 MPa, and even when the high-performance decomposition catalyst is used, the decomposition rate of the ammonia decomposition reaction will be, for example, 95-97%.

[0114] The heat-insulating heater 1a can be placed outside or inside the container body of the tank 1. Preferably, the heat-insulating heater 1a indirectly heats the liquefied ammonia. The heat-insulating heater 1a may use a heating mechanism such as a heat exchanger or heater with a temperature control function, or it may use an insulating material that covers the outside of the container body of the tank 1, or a combination of these. Heating of the inside of the tank 1 by the heat-insulating heater 1a can be performed intermittently or continuously during the operation of the hydrogen gas production apparatus A3. If performed intermittently, it is started when the temperature or internal pressure inside the tank 1, measured during the operation of the hydrogen gas production apparatus A3, reaches a predetermined lower limit and stopped when it reaches a predetermined upper limit.

[0115] Furthermore, as liquefied ammonia is continuously supplied downstream, the amount of liquefied ammonia in tank 1 decreases. Normally, the liquefied ammonia in tank 1 vaporizes to fill the gas phase space, and the heat of vaporization is removed during this process, causing the tank 1 to cool down. Therefore, the temperature and pressure inside tank 1 will gradually decrease during operation unless the amount of heat lost due to vaporization is compensated for by external heating. For this reason, during the operation of the hydrogen gas production device A3, the temperature and internal pressure inside tank 1 can be maintained by continuously heating the inside of tank 1 with the heat-insulating heater 1a to compensate for the amount of heat lost due to vaporization, thereby preventing this cooling from progressing.

[0116] In the embodiments described above, we have described a configuration in which the primary purification section 15 is an ammonia adsorption section 15 and the secondary purification section 19 is a hydrogen separation section 19, as in the hydrogen gas production apparatus A1 and A3. According to these embodiments, residual ammonia gas is removed in the ammonia adsorption section 15 before hydrogen gas is separated in the hydrogen separation section 19. As a result, there is almost no residual ammonia gas remaining in the residual gas (nitrogen-based gas) separated from the hydrogen gas in the hydrogen separation section 19, and its concentration (less than several hundred ppb by volume after removal of residual ammonia gas, preferably less than 100 ppb by volume) is low enough not to violate regulations concerning odors (the regulatory standard at the site boundary under Japan's Odor Prevention Law is 2 ppm by volume in industrial areas and exclusive industrial areas, and 1 ppm by volume elsewhere), and if the hydrogen gas concentration in the residual gas is below the lower limit of combustion, it can be released directly into the atmosphere. Therefore, there is no need to remove residual ammonia gas from the residual gas separated from the hydrogen gas in the hydrogen separation section 19, and the equipment is simplified.

[0117] On the other hand, according to an embodiment other than the one described above, as shown in Figure 4, the primary purification section 15 may be a hydrogen separation section, and the secondary purification section 19 may be an ammonia adsorption section. Figure 4 is a diagram of a hydrogen gas production apparatus A4 according to one embodiment. Figure 4 shows a case in which the aforementioned pressurizer 17a is not provided upstream of the separation membrane of the hydrogen separation section, but the pressurizer 17a may be provided, and the effects in each case are the same as those described above. In this embodiment as well, liquefied ammonia, ammonia gas, decomposition gas, primary purified gas (here, a gas mainly composed of hydrogen gas and containing residual ammonia gas that has not been decomposed in the ammonia decomposition section 9), and secondary purified gas (here, a hydrogen-based gas from which residual ammonia gas has been removed from the primary purified gas) flow downstream through the raw ammonia line 3, decomposition gas line 11, primary purified gas line 17, and secondary purified gas line 21, respectively, due to the pressure difference between the vapor pressure of the ammonia gas vaporized in the tank 1 and the pressure on the upstream side of the vacuum pump 22, which is located downstream of the separation membrane of the primary purification section (hydrogen separation section) 15 and decomposes the primary purified gas. Throughout the above process, it is necessary to maintain the internal pressure (vapor pressure) of tank 1 at a predetermined supply pressure so that liquefied ammonia and a series of gases flow downstream from tank 1 to the secondary purified gas line 21 without stagnation. For this reason, it is preferable that tank 1 be further provided with a heat-insulating heater 1a to heat the inside and maintain the required internal pressure (vapor pressure) (not shown in Figure 4). In the hydrogen gas production apparatus A4, the permeation rate per unit time of hydrogen-based gas containing a trace amount of residual ammonia gas separated and permeated by the separation membrane (approximately equal to the amount of secondary purified gas produced per unit time in the hydrogen gas production apparatus A4), and the required number of parallel separation membrane modules are determined by the aforementioned equations 1 and 2, respectively.

[0118] Returning to Figure 3, in this embodiment, the hydrogen gas production apparatus A3 may further include a second cooler 27 provided upstream or downstream of the cooler 13 (hereinafter referred to as the first cooler 13) in the decomposition gas line 11, as shown in Figure 3, to cool the decomposition gas. In the hydrogen gas production apparatus A3 shown in Figure 3, the second cooler 27 is provided downstream of the first cooler 13. The removal rate of residual ammonia gas by the ammonia adsorption unit 15 increases as the temperature of the decomposition gas decreases, preferably to around room temperature (about 25°C) or lower. Therefore, if the cooling capacity of the first cooler 13 is insufficient and the temperature of the decomposition gas after cooling is several tens of degrees Celsius or more higher than room temperature (for example, about 25°C), cooling by the second cooler 27 can compensate for the insufficient cooling by the first cooler 13 and increase the removal rate of residual ammonia gas.

[0119] Furthermore, in this embodiment, the second cooler 27 can be a heat exchanger structure, a forced air cooling structure using an air cooling fan or the like, or an electronically cooled structure. Of these, it is preferable that the decomposition gas passing through the second cooler 27 having a heat exchanger structure is cooled by heat exchange with outside air or a liquid refrigerant cooled by heat exchange with outside air. When the second cooler 27 is provided upstream of the first cooler 13, it is preferable to use air taken into the second cooler 27 from the outside as the refrigerant. When the second cooler 27 is provided downstream of the first cooler 13, it is preferable to use a liquid refrigerant, such as cooling water cooled by heat exchange with outside air by a radiator (not shown), as the refrigerant. The liquid refrigerant can be circulated so that after heat exchange with the decomposition gas in the second cooler 27, it is returned to the radiator, cooled again by heat exchange with outside air, and used in the second cooler 27.

[0120] According to one embodiment, the ammonia adsorption unit 15 preferably includes, as shown in Figure 2, a regeneration heater 35 for heating the adsorbent that has adsorbed residual ammonia gas, an inert gas introduction line 37 for introducing an inert gas from the outside, and a desorbed ammonia discharge line 39 through which residual ammonia gas desorbed from the adsorbent flows. The ammonia adsorption unit 15 is configured such that residual ammonia gas adsorbed on the adsorbent is desorbed from the adsorbent by heating it with the regeneration heater 35, and together with the inert gas introduced through the inert gas introduction line 37, it is discharged from the ammonia adsorption unit 15 through the desorbed ammonia discharge line 39. As a result, when the adsorbent of the ammonia adsorption unit 15 reaches breakthrough due to the adsorption of residual ammonia gas, etc., the adsorbent is heated to desorb the adsorbed residual ammonia gas, etc., regenerates the adsorbent, and allows for repeated use.

[0121] For example, an electric heater can be used for the regeneration heater 35. In the example shown in Figure 2, the regeneration heater 35 is installed in the ammonia adsorption unit 15 apparatus (for example, the adsorption tower described above), and heats the adsorbent together with the ammonia adsorption unit 15 apparatus. For example, if the adsorbent is an X-type zeolite, heating it to approximately 400°C or higher will cause more than 90% of the adsorbed ammonia gas to be desorbed.

[0122] In the example shown in Figure 2, the inert gas introduction line 37 is connected to the primary purification gas line 17. The portion of the inert gas introduction line 37 extending from the connection point with the primary purification gas line 17 to the ammonia adsorption unit 15 shares a portion of its flow path with the primary purification gas line 17. In the example in Figure 2, the inert gas passes through the inert gas introduction line 37 and flows in the opposite direction to the primary purification gas within this flow path before being introduced into the ammonia adsorption unit 15. The inert gas is preferably a gas that does not chemically react with ammonia and does not substantially inhibit the adsorption of ammonia gas onto the adsorbent. Nitrogen gas, argon gas, helium gas, and other noble gases are preferably used. Nitrogen gas is shown as an example in the drawing.

[0123] In the example shown in Figure 2, the desorbed ammonia discharge line 39 is connected to the decomposition gas line 11. The portion of the desorbed ammonia discharge line 39 extending from the ammonia adsorption unit 15 to the connection point with the decomposition gas line 11 partially shares a flow path with the decomposition gas line 11. The portion of the desorbed ammonia discharge line 39 extending from this connection point toward the combustor 29 shares a flow path with the branch gas line 30 that branches off from the decomposition gas line 11. In the example in Figure 2, the desorbed ammonia gas, together with the inert gas, flows in the opposite direction to the decomposition gas through the former of the two flow paths, and then flows in the same direction as the off-gas through the latter flow path and is discharged through the desorbed ammonia discharge line 39.

[0124] It should be noted that the introduction of the inert gas into the ammonia adsorption section 15 does not necessarily have to be in the direction described above as shown in Figure 2. The inert gas may also be introduced from the upstream side of the ammonia adsorption section 15 in the same direction as the decomposition gas (in this case, the inert gas introduction line 37 is connected to the upstream part of the ammonia adsorption section 15). In that case, the ammonia gas desorbed from the ammonia adsorption section 15 flows together with the inert gas toward the downstream side of the ammonia adsorption section 15 in the same direction as the primary purified gas flows and is discharged (in this case, the desorbed ammonia discharge line 39 is connected to the downstream part of the ammonia adsorption section 15).

[0125] In this embodiment, the hydrogen gas production apparatus A2 preferably further comprises the combustor 29 described above, as shown in Figure 2. The ammonia gas discharged together with the inert gas is led to the combustor 29 and burned. Since the off-gas supplied to the combustor 29 contains highly combustible hydrogen gas, the ammonia gas that has been desorbed from the adsorbent in the ammonia adsorption section 15 and discharged can be burned together with the hydrogen gas, rendering it harmless and odorless. This allows ammonia gas, whose release into the atmosphere is restricted, to be treated by incineration. Because the configuration of this embodiment can be designed to be relatively compact, the hydrogen gas production apparatus A2 can be suitably used in small on-site facilities or mobile units.

[0126] Furthermore, in this embodiment, the heating element 7 is provided downstream of the vaporizer 5 in the raw ammonia line 3, and the hydrogen gas production apparatus A2 is connected to the combustor 29 and further comprises a combustion gas line 31 through which the combustion gas flows, and it is preferable that a part of the combustion gas line 31 and the heating element 7 constitute the first heat exchanger 33 described above.

[0127] In one embodiment, the ammonia adsorption unit 15 comprises a regeneration heater 35, an inert gas introduction line 37, and a desorbed ammonia discharge line 39. In this embodiment, the hydrogen gas production apparatus A further comprises a reliquefaction unit (gas-liquid separator) 41, which is connected to the desorbed ammonia discharge line 39 and the tank 1, and is configured to separate the ammonia gas desorbed from the adsorbent from the inert gas by liquefying it, as shown in Figure 14, which will be referenced later. The ammonia gas discharged together with the inert gas is led to the reliquefaction unit (gas-liquid separator) 41, where it is separated from the inert gas by liquefaction and recovered in the tank 1. The inert gas separated from the liquefied ammonia in the reliquefaction unit (gas-liquid separator) 41 is discharged outside the system after any remaining ammonia is removed by adsorption or the like. Preferably, the desorbed ammonia discharge line 39 is provided with a compressor 42 for compressing the ammonia gas and a cooler 43. This allows the ammonia gas desorbed from the adsorbent, discharged, and compressed to be efficiently cooled, liquefied, and recovered. According to this embodiment, the outflow of desorbed ammonia gas into the external environment can be minimized by returning the ammonia gas, whose release into the atmosphere is restricted, back to liquefied ammonia in tank 1, which is the raw material for hydrogen gas. A pump, for example, is used for the compressor 42. Since the reliquefaction unit (gas-liquid separator) 41 is generally a relatively large device, the hydrogen gas production apparatus A of this embodiment can be suitably used in a somewhat large on-site facility or a somewhat large mobile device (for example, a ship). Furthermore, the configuration of this embodiment can be used in combination with the configuration of the above-described embodiment, in which the ammonia gas discharged from the ammonia adsorption unit 15 is burned by the combustor 29.

[0128] In the above embodiment, which employs a configuration in which residual ammonia gas discharged from the ammonia adsorption unit 15 is burned by the combustor 29, the ammonia adsorption unit 15 preferably has a plurality of ammonia adsorbents 15A and 15B arranged in parallel with respect to the gas flow direction, as shown in Figure 6, which will be referenced later. Preferably, the above-described adsorption tower is used for each of the plurality of ammonia adsorbents 15A and 15B. The number of plurality of ammonia adsorbents provided in the ammonia adsorption unit 15 is two in the illustrated example, but is not limited to two and may be three, four or more.

[0129] Each of the multiple ammonia adsorbents 15A has the adsorbent described above, an inert gas introduction line 37A, and a desorbed ammonia discharge line 39A. Each of the multiple ammonia adsorbents 15B has the adsorbent described above, an inert gas introduction line 37B, and a desorbed ammonia discharge line 39B. The adsorbents in the ammonia adsorbents 15A and 15B are configured in the same way as the adsorbents described above, and the same type of adsorbent can be used for each. In all cases, the adsorbed ammonia gas can be desorbed by heating and regenerated.

[0130] In the example shown in Figure 6, the inert gas introduction lines 37A and 37B are the parts that branch off from the inert gas supply port 37c and extend in two directions, connecting to the ammonia adsorbents 15A and 15B, and are connected to each other at the supply port 37c. The inert gas supplied from the supply port 37c is introduced from the supply port 37c through the inert gas introduction lines 37A and 37B to the ammonia adsorbents 15A and 15B. In the example shown in Figure 6, the primary purification gas line 17 extends from each of the ammonia adsorbents 15A and 15B, merges, and extends toward the hydrogen separation section 19. The portions of the primary purification gas line 17 extending from each of the ammonia adsorbents 15A and 15B are connected to the inert gas introduction lines 37A and 37B and share a flow path with the inert gas introduction lines 37A and 37B.

[0131] In the example shown in Figure 6, the desorbed ammonia discharge lines 39A and 39B extend from the ammonia adsorbents 15A and 15B respectively, merge, and extend toward the combustor 29. In the example shown in Figure 6, the decomposition gas line 11 branches into two on its way from the ammonia decomposition section 9 toward the ammonia adsorption section 15, and connects to the ammonia adsorbents 15A and 15B respectively. The portions of the decomposition gas line 11 connected to the ammonia adsorbents 15A and 15B share a flow path with the inert gas introduction lines 37A and 37B. Also in the example shown in Figure 6, the branched gas line 30 is connected to the point where the desorbed ammonia discharge lines 39A and 39B merge, and shares a flow path with the desorbed ammonia discharge lines 39A and 39B.

[0132] Preferably, the ammonia adsorption section 15 is configured such that, while residual ammonia gas, which has been desorbed from the adsorbent in one or more of the multiple ammonia adsorbents by heating with a regeneration heater 35, is discharged through the desorbed ammonia discharge line 39 together with the inert gas introduced from the inert gas introduction line 37, decomposition gas or primary purified gas is introduced into the remaining ammonia adsorbents, and residual ammonia gas in the gas is removed by adsorption onto the adsorbent of the ammonia adsorbent, and the decomposition gas or primary purified gas from which the residual ammonia gas has been removed is led downstream of the ammonia adsorption section. Preferably, the ammonia adsorption section 15 is configured such that one or more ammonia adsorbents and the remaining ammonia adsorbents can be switched between. This switching is performed by the coordinated switching operation of valves (for example, having the structure of a three-way valve) at the branching point of the decomposition gas line 11 and the confluence point of the desorbed ammonia discharge line 39, at a timing before the adsorbent adsorbing ammonia gas reaches breakthrough. According to this embodiment, by repeatedly switching between an ammonia adsorbent that adsorbs residual ammonia gas (use of adsorbent) and an ammonia adsorbent that desorbs residual ammonia gas (regeneration of adsorbent), the use and regeneration of the adsorbent can be performed simultaneously and continuously, eliminating the need to stop the operation of the hydrogen gas production apparatus A, and allowing for continuous operation for a long period of time. In this embodiment, a portion of the combustion gas generated by burning off-gas in the combustor 29 is guided to the first heat exchanger 33 through the combustion gas line 31, and while raising the temperature of the ammonia gas, a portion of the remaining combustion gas is guided through the regeneration gas line 28 to the ammonia adsorbent that regenerates the adsorbent, and heated by contacting the outer wall surface of the ammonia adsorbent apparatus (adsorption tower). The regeneration gas line 28 extends from the combustor 29 toward the ammonia adsorption section 15, and then splits into two branches to connect to ammonia adsorbents 15A and 15B, respectively. Such a configuration contributes to reducing energy loss when adsorbing residual ammonia gas at low temperatures and desorbing residual ammonia gas at high temperatures are performed in parallel.

[0133] In the example shown in Figure 6, the inert gas flows through the inert gas introduction line 37A or 37B, through the primary purified gas line 17 in the opposite direction to the primary purified gas, and is introduced into the ammonia adsorbent 15A or 15B. Also in the example shown in Figure 6, the desorbed ammonia gas flows together with the inert gas through the decomposition gas line 11 in the opposite direction to the decomposition gas, and then flows through the desorbed ammonia discharge line 39A or 39B in the same direction as the off-gas and is discharged. However, the direction of introduction of the inert gas to the ammonia adsorbent 15A or 15B does not have to be this direction; the inert gas may be introduced from the upstream side of the ammonia adsorbent 15A or 15B in the same direction as the decomposition gas (in this case, the inert gas introduction lines 37A and 37B are connected to the upstream part of the ammonia adsorbent 15A or 15B). In this case, the ammonia gas desorbed from the ammonia adsorbers 15A and 15B flows together with the inert gas toward the downstream side of the ammonia adsorbers 15A and 15B, in the same direction as the primary purified gas, and is discharged (in this case, the desorbed ammonia discharge lines 39A and 39B are connected to the downstream portion of the ammonia adsorption section 15).

[0134] In one embodiment, as shown in Figure 5, the ammonia adsorption section 15 preferably has two ammonia adsorbents 15X and 15Y arranged in series in the direction of gas flow, and each of the two ammonia adsorbents 15X and 15Y has an adsorbent. Each of the multiple ammonia adsorbents 15X and 15Y uses a structure similar to that of the adsorption tower described above. In the example shown in Figure 5, the two ammonia adsorbents 15X and 15Y are connected to each other in the direction of gas flow by a connecting line 15a. The gas from which residual ammonia gas has been adsorbed in ammonia adsorbent 15X is guided to ammonia adsorbent 15Y through the connecting line 15a.

[0135] According to this embodiment, residual ammonia gas remaining in the gas after passing through the upstream ammonia adsorbent (hereinafter referred to as the primary adsorbent) 15X is removed by adsorption onto the adsorbent in the downstream ammonia adsorbent (hereinafter referred to as the secondary adsorbent) 15Y, thereby further reducing the concentration of residual ammonia gas in the purified gas. The residual ammonia in the purified gas after passing through the secondary adsorbent 15Y is preferably less than 100 ppb by volume. This improves the effect of preventing electrode poisoning by residual ammonia gas when the secondary purified gas is supplied to a polymer electrolyte fuel cell (PEFC).

[0136] Preferably, the adsorbent for the primary adsorbent 15X is a solid Lewis acid type adsorbent, similar to the one used when there is only one adsorbent. Specifically, porous adsorbents with many Lewis acid sites, such as zeolites of type X or type A, are used. Zeolites with many pores of 5 to 20 Å in diameter, particularly zeolite 13X, are well used. These zeolites preferably contain at least one cation from lithium (Li), calcium (Ca), and sodium (Na). These adsorbents can be regenerated by heating them on-site when breakthrough occurs due to the adsorption of ammonia gas, etc., thereby desorbing the ammonia gas, etc., and thus can be reused repeatedly.

[0137] Preferably, the adsorbent used in the secondary adsorbent 15Y is a Brønsted acid type or a metal complex compound type adsorbent. Specifically, Brønsted acid type adsorbents are those that have Brønsted acid sites, high acidity, and large exchange capacity, such as activated carbon, silica gel, or alumina gel whose surfaces have been acid-treated with or impregnated with a strong non-volatile acid such as activated alumina, silica-alumina gel, sulfuric acid, or phosphoric acid, zirconium phosphate, zirconium phosphonate, or ion exchange resins having strongly acidic or super-strongly acidic ion exchange groups (for example, hydrocarbon or fluorocarbon polymers having many sulfonic acid groups and sulfate groups). 3+) and hexacyanoferrate(II) ions (Fe[CN]6 4- ) and has a three-dimensionally connected structure, or a structure in which part of the central metal iron (Fe) is substituted with cobalt (Co) or copper (Cu), or a structure in which part of the hexacyanoferrate(II) ions (Fe[CN]6 4- ) ions are missing, such as Prussian blue analogs, are used. These adsorbents of Prussian blue and Prussian blue analogs have the advantage that when moisture coexists in the decomposition gas, they adsorb only ammonia and hardly adsorb moisture. These adsorbents generally have stronger ammonia gas adsorption performance than the aforementioned adsorbents used in the primary adsorber 15X. However, it is difficult to desorb and regenerate the adsorbed ammonia gas by a simple on-site heating operation such as that performed on the adsorbent of the primary adsorber 15X. Therefore, when breakthrough of the secondary adsorber 15Y is reached, these adsorbents are removed from the device of the secondary adsorber 15Y and replaced with new ones. Alternatively, depending on the above-mentioned Bronsted acid type adsorbent, or if the secondary adsorber 15Y is configured such that an operation such as flowing a diluted acid of a strong acid or superacid can be performed during the operation stop of the hydrogen gas production apparatus A, by flowing a diluted acid of a strong acid or superacid through the breakthrough adsorbent, ammonium ions (NH4 + ) adsorbed on the adsorbent may be exchanged with hydrogen ions (H + ) and regenerated. In addition, in some cases, the adsorbent removed at the breakthrough point can be regenerated and reused by performing the above-mentioned regeneration treatment by ion exchange offline. Also, for adsorbents such as activated alumina and silica-alumina gel, regeneration treatment by offline calcination may be effective. Furthermore, the above-mentioned adsorbents of Prussian blue and Prussian blue analogs can also be regenerated online or offline by flowing a diluted acid of a strong acid. Usually, since most of the residual ammonia gas is adsorbed by the primary adsorber 15X, the substantial amount of residual ammonia gas adsorbed by the adsorbent of the secondary adsorber 15Y is very small. Therefore, the adsorbent of the secondary adsorber 15Y can often be used for a relatively long time even in small amounts.

[0138] In one embodiment, as shown in Figure 7, the ammonia adsorption unit 15 includes a plurality of upstream ammonia adsorbents 15A, 15B (all corresponding to primary adsorbents 15X) arranged in parallel with respect to the gas flow direction, and at least one downstream ammonia adsorbent 15Y (corresponding to a secondary adsorbent) arranged in series in one direction with at least one of the upstream ammonia adsorbents 15A, 15B, and 15Y, and it is preferable that each of the ammonia adsorbents 15A, 15B, and 15Y contains an adsorbent. In this embodiment, a plurality of primary adsorbents 15X (15A, 15B, ...) containing an adsorbent that can be regenerated on-site by heating and the flow of an inert gas are arranged in parallel on the upstream side, and one or more secondary adsorbents 15Y, which have stronger ammonia adsorption performance but contain an adsorbent that cannot be regenerated on-site by heating and the flow of an inert gas, are provided in series downstream of these adsorbents. The piping and operation of the above adsorbents are carried out in accordance with the above description.

[0139] According to this embodiment, by passing the decomposition gas cooled via the cooler 13 through at least one of the multiple primary adsorbents 15X (15A, 15B, ...) arranged in parallel on the upstream side, most of the residual ammonia in the decomposition gas can be adsorbed and removed. At the same time, the adsorbent inside the remaining primary adsorbents can be regenerated by heating them and passing inert gas through them. Furthermore, by simultaneously passing the decomposition gas that has passed through at least one of the multiple primary adsorbents 15X (15A, 15B, ...) arranged in parallel on the upstream side through one or more secondary adsorbents 15Y arranged in series on the downstream side, it is possible to more effectively adsorb and remove residual ammonia gas that could not be adsorbed and removed by the upstream primary adsorbents 15X (15A, 15B, ...). Furthermore, the adsorbents in the multiple primary adsorbents 15X (15A, 15B, ...) arranged in parallel on the upstream side can be easily regenerated online by heating and the flow of an inert gas, allowing for continued use. The adsorbents in the secondary adsorbent 15Y located downstream are replaced periodically after being used for a relatively long period of time, and can also be regenerated offline by the flow of a dilution of a strong acid, depending on the circumstances.

[0140] According to one embodiment, the hydrogen gas production apparatus A preferably includes a flow regulator 6, which is provided downstream of the vaporizer 5 in the raw ammonia line 3 and adjusts the flow rate of ammonia gas, as shown in Figure 1, etc.

[0141] The flow regulator 6 is a device that adjusts the flow rate of ammonia gas to a predetermined flow rate. The flow regulator 6 can be a mass flow meter, an ultrasonic flow meter, an electromagnetic flow meter, or the like. The amount of liquefied ammonia processed per unit time is set according to the mass flow rate of ammonia gas adjusted by the flow regulator 6. This amount of liquefied ammonia processed per unit time is determined by the following formula, based on the amount of primary purified gas processed per unit time by the separation membrane of the hydrogen separation unit 19. Formula 3: (Processing rate of liquefied ammonia per unit time [kg-NH3 / h]) = (Amount of ammonia adsorbed per unit time at the ammonia adsorption section 15 [kg-NH3 / h]) +(Amount of primary purified gas processed per unit time at the separation membrane in the hydrogen separation section 19 [kg-H2 / h]) + (Off-gas extraction rate per unit time [kg / h])

[0142] In Equation 3, the amount of ammonia adsorbed per unit time in the first term is approximately equal to the amount of residual ammonia per unit time in the ammonia decomposition unit 9 (= decomposition gas flow rate × residual ammonia gas concentration). The amount of off-gas extracted per unit time in the third term needs to be considered when the off-gas is branched downstream of the ammonia decomposition unit 9 in order to obtain the combustion gas necessary for heating the ammonia gas in the second heat exchanger 25 or for incinerating the ammonia gas desorbed from the adsorbent in the ammonia adsorption unit 15.

[0143] Based on the rate of liquefied ammonia processed per unit time determined by Equation 3, the following are also set: (i) the amount of heat exchanged per unit time in each heat exchange unit (for example, the second heat exchanger 25 and the first heat exchanger 33), (ii) the required amount of catalyst based on the flow rate of the gas to be treated in the ammonia decomposition unit 9, (iii) the required amount of adsorbent in the ammonia adsorption unit 15, and (iv) the required number of parallel separation membrane modules in the hydrogen separation unit (according to Equation 2 mentioned above).

[0144] (Hydrogen gas supply device) Next, the hydrogen gas supply device of the embodiment will be described.

[0145] Figure 8 shows a hydrogen gas supply device B1 according to one embodiment. Figure 9 shows a hydrogen gas supply device B2 according to one embodiment. In the following description, hydrogen gas supply devices B1 and B2 may be collectively referred to as hydrogen gas supply device B. Hydrogen gas supply device B is a device that supplies hydrogen gas to a recipient. Hydrogen gas supply device B comprises the hydrogen gas production device A described above and a purified gas tank 63. More specifically, hydrogen gas supply device B2 comprises a final gas discharge line 61, a purified gas tank 63, a pressurizer 65, and a set of switching valves 67.

[0146] The final gas discharge line 61 is connected to the secondary purified gas line 21 of the hydrogen gas production apparatus A, and is a final gas discharge line 61 that guides the secondary purified gas discharged from the secondary purified gas line 21 toward the supply destination and discharges it, and has a branching section 61a that branches so that the secondary purified gas flows to a side different from the supply destination side. Examples of supply destinations include fuel cells and high-pressure hydrogen tanks, which will be described later.

[0147] The purified gas tank 63 is connected to the branching section 61a and is a container for storing the secondary purified gas that flows to the side opposite to the supply destination. The purified gas tank 63 may be, for example, a high-pressure tank in which the internal pressure is maintained at, for example, 80 MPa to 90 MPa when filled with secondary purified gas (for example, the purified gas tank 63 shown in Figure 9 and Figure 13, which will be referenced later), or a simple tank (buffer tank) for the temporary storage of a small amount of secondary purified gas may be used (for example, the purified gas tank 63 shown in Figure 8 and Figure 12, which will be referenced later). The high-pressure tank can be suitably used as the purified gas tank 63 when the hydrogen gas supply device B is installed, for example, at a hydrogen station that supplies hydrogen gas to mobile vehicles such as fuel cell vehicles (FCVs). The hydrogen gas supply device B in the illustrated example has only one purified gas tank 63, but the number of purified gas tanks that the hydrogen gas supply device B has may be two, three or more. The hydrogen gas supply device B may include, for example, a plurality of small tanks connected in parallel to each other at the branching section 61a, as multiple purified gas tanks 63. As small tanks, for example, accumulators that store secondary purified gas at a high pressure of 10 to 90 MPa can be used.

[0148] The pressurizer 65 is installed upstream of the branch 61a in the final gas discharge line 61 and is a device that pressurizes the secondary purified gas into the purified gas tank 63. The pressurizer 65 can use a pump or a compressor, and these can be used in combination. In the examples shown in Figures 9 and 13, the purified gas tank 63 is the high-pressure tank, and the pressurizer 65 is a compressor capable of pressurizing the secondary purified gas into the purified gas tank 63 at high pressure. The pressurizer 65 can not only make the pressure downstream of the pressurizer 65 higher than the pressure upstream of the pressurizer 65, but at the same time reduce the pressure upstream of the pressurizer 65, so it can also serve as a vacuum pump 22 installed in the secondary purified gas line 21, and in some cases the vacuum pump 22 can be omitted from the secondary purified gas line 21. In a device in which the vacuum pump 22 is omitted, the vacuum pump 22 of the hydrogen gas production device A is composed of the pressurizer 65, and the secondary purified gas line 21 of the hydrogen gas production device A is composed of the secondary purified gas line 21 and the final gas discharge line 61.

[0149] A pair of switching valves 67 is installed in the final gas discharge line 61 and switches the flow path of the secondary purified gas flowing through the final gas discharge line 61. In the example shown in Figures 9 and 13, the pair of switching valves 67 includes a valve 67a installed upstream of the branch 61a of the final gas discharge line 61, a valve 67b installed at the branch 61a, and a valve 67c installed downstream of the branch 61a of the final gas discharge line 61. The pair of switching valves 67 is configured to switch between directing the secondary purified gas discharged from the secondary purified gas line 21 toward the purified gas tank 63, guiding the secondary purified gas in the purified gas tank 63 toward the supply destination and discharging it, or guiding the secondary purified gas discharged from the secondary purified gas line 21 toward the supply destination and discharging it, by switching the open and closed states of these valves 67a to 67c.

[0150] Hydrogen gas supply device B is suitably used as an on-site hydrogen station for supplying hydrogen gas to mobile vehicles such as fuel cell vehicles (FCVs). The liquefied ammonia supplied from an external source to tank 1 of hydrogen gas production device A can be transported using a transport means such as a tank truck.

[0151] According to one embodiment, it is preferable that a third cooler 69 is provided downstream of the branch section 61a in the final gas discharge line 61. This prevents the external tank from overheating due to adiabatic compression of the secondary purified gas when the high-pressure secondary purified gas stored in the purified gas tank 63 is rapidly supplied and stored in, for example, an external tank. Cooling by the third cooler 69 is effective when the purified gas tank 63 is the high-pressure tank. The external tank is, for example, a high-pressure hydrogen tank mounted on a mobile vehicle such as a fuel cell vehicle (FCV). The secondary purified gas is cooled to a cooling temperature of, for example, -40 to -30°C by the third cooler 69. For example, a heat exchanger that performs heat exchange between the secondary purified gas and a refrigerant can be used as the third cooler 69. The refrigerant used is a refrigerant that is cooled by a powerful external cooling source (for example, a refrigerator) and is usable at the above cooling temperature.

[0152] According to one embodiment, it is preferable that a fourth cooler 62 is provided upstream of the pressurizer 65 in the final gas discharge line 61. When the purified gas tank 63 is the high-pressure tank and the pressurizer 65 is a compressor capable of injecting secondary purified gas into the purified gas tank 63 at high pressure, pre-cooling the secondary purified gas with the fourth cooler 62 before it is compressed by the pressurizer 65 can prevent the purified gas tank 63 from overheating due to adiabatic compression of the secondary purified gas by the pressurizer 65. The secondary purified gas is cooled to a cooling temperature of, for example, -40 to -30°C. For the fourth cooler 62, for example, a heat exchanger that performs heat exchange between the secondary purified gas and a refrigerant can be used. As the refrigerant, a refrigerant that is usable at the above cooling temperature and cooled by a powerful external cooling source (for example, a refrigerator) is used.

[0153] (Fuel cell system) Next, the fuel cell system C of the embodiment will be described.

[0154] Figures 10 to 17 show fuel cell systems C1 to C11. Figure 10 is a diagram showing the configuration of fuel cell system C1 according to one embodiment. Figure 11 is a diagram showing the configuration of fuel cell system C2 according to one embodiment. Figure 12 is a diagram showing the configuration of fuel cell system C3 according to one embodiment. Figure 13 is a diagram showing the configuration of fuel cell system C4 according to one embodiment. Figure 14 is a diagram showing the configuration of fuel cell system C5 according to one embodiment. Figure 15 is a diagram showing the configuration of fuel cell system C6 according to one embodiment. Figure 16 is a diagram showing the configuration of fuel cell system C7 according to one embodiment. Figure 17 is a diagram showing the configuration of fuel cell system C8 according to one embodiment. In the following description, fuel cell systems C1 to C8 will be collectively referred to as fuel cell system C.

[0155] The fuel cell system C comprises the hydrogen gas production device A or the hydrogen gas supply device B described above, and a polymer electrolyte fuel cell (PEFC) 81. Because polymer electrolyte fuel cells (PEFCs) have high power generation efficiency, low operating temperature, and are lightweight and compact, the fuel cell system C is suitable for use as a power generation system in mobile devices such as fuel cell vehicles (FCVs) or in on-site facilities for home or commercial use.

[0156] The polymer electrolyte fuel cell (PEFC) 81 is equipped with a negative electrode and a positive electrode, which are connected to an external load 91. It is configured to generate electricity when hydrogen gas discharged from a hydrogen gas production device A or a hydrogen gas supply device B is supplied to the negative electrode and air is supplied to the positive electrode. When generating electricity with the polymer electrolyte fuel cell 81, the required flow rate of hydrogen gas supplied from the hydrogen gas production device A or the hydrogen gas supply device B is determined according to its output current value.

[0157] A polymer electrolyte fuel cell (PEFC) 81 has a single cell comprising a catalyst layer with gas diffusion layers on both sides of a polymer electrolyte membrane, and a separator which is a current collector, stacked together. Preferably, a cell stack has a bipolar structure in which multiple single cells are stacked in series. The cell stack has a negative electrode terminal connected to the negative electrode of each single cell and a positive electrode terminal connected to the positive electrode of each single cell. The illustrated polymer electrolyte fuel cell (PEFC) 81 constitutes a cell stack, and the negative electrode terminal and the positive electrode terminal are connected to an external load 91.

[0158] The negative electrode catalyst layer of the single cell is a layer made of carbon black supporting a catalyst, for example, ultrafine particles of platinum group metals such as platinum (Pt), and the positive electrode catalyst layer is a layer made of carbon black supporting a catalyst, for example, ultrafine particles of platinum group metal oxides such as iridium (Ir) oxide. These are bonded to both sides of the electrolyte membrane, respectively, and constitute the negative electrode and positive electrode of the polymer electrolyte fuel cell (PEFC) 81. The electrolyte membrane is made of a highly acidic fluorocarbon polymer that mainly has ion exchange groups such as sulfonic acid groups and carboxyl groups, and has a high hydrogen ion (hydronium ion H3O) + ) has conductivity. The separator often uses thin plates made of graphite, carbonaceous material, or composite materials containing these, which have sufficient electronic conductivity and mechanical strength and are chemically stable in bonding with superacidic electrolytes and in the reduction / oxidation environment of the negative and positive electrodes. By connecting an external load 91 between the negative electrode terminal and the positive electrode terminal and supplying hydrogen gas and oxygen gas to the negative and positive electrodes, respectively, DC power is output and electricity can be generated. At this time, if gas components such as carbon monoxide, ammonia, hydrogen sulfide, or sulfur compounds such as sulfur dioxide are mixed in the hydrogen gas supplied to the negative electrode of the polymer electrolyte fuel cell (PEFC) 81, the platinum or other negative electrode catalyst will be strongly poisoned by these gas components, reducing the catalytic activity and significantly decreasing the power generation performance of the polymer electrolyte fuel cell (PEFC). For this reason, the concentration of these gas components in the secondary purified gas needs to be reduced to within an acceptable range that does not cause such poisoning, and it is preferable that it be within the acceptable range specified in ISO 14687-2, the international standard for hydrogen gas for fuel cells.

[0159] A hydrogen gas supply pump 79 is provided downstream of the pressure reducer 22 in the final gas discharge line 61. The hydrogen gas supply pump 79 is a device for supplying a secondary purified gas containing a high concentration of hydrogen gas to the polymer electrolyte fuel cell (PEFC) 81. The secondary purified gas of the fuel supplied to the polymer electrolyte fuel cell 81 generally contains hydrogen ions (hydronium ions H3O) in the electrolyte membrane. + Although moisture (water vapor) is added to mediate the conduction of ), the lines for adding this moisture (water vapor) are omitted in Figures 10 to 17.

[0160] A hydrogen gas supply line 83, which is connected to the final gas discharge line 61 via a hydrogen gas supply pump 79, is connected to the hydrogen gas supply port of the polymer electrolyte fuel cell (PEFC) 81, which supplies secondary purified gas to the negative electrode of the polymer electrolyte fuel cell (PEFC) 81. On the other hand, a hydrogen gas discharge line 84 is connected to the hydrogen gas discharge port of the polymer electrolyte fuel cell 81, which discharges gas containing excess hydrogen gas that was not consumed during power generation (hereinafter referred to as hydrogen-containing gas) from the negative electrode of the polymer electrolyte fuel cell 81. A pressure regulator 85 is provided in the hydrogen gas discharge line 84, and downstream of the pressure regulator 85, the hydrogen gas discharge line 84 is connected to the final gas discharge line 61. The combined hydrogen-containing gas, together with the secondary purified gas discharged from the final gas discharge line 61, is supplied to the negative electrode of the polymer electrolyte fuel cell 81, thereby forming a hydrogen gas circulation loop via the negative electrode. Furthermore, the hydrogen gas discharge line 84 is equipped with a flow path switch 86, and a hydrogen gas treatment line 87 is provided, which branches off from the hydrogen gas discharge line 84 via the flow path switch 86 and discharges the hydrogen-containing gas to the outside. For example, a three-way valve can be used as the flow path switch 86. The flow path switch 86 switches the flow path of the hydrogen-containing gas so that the hydrogen-containing gas flows in either the direction toward the final gas discharge line 61 or toward the outside. In normal operating conditions, the flow path switch 86 is set so that the hydrogen-containing gas flows from the hydrogen gas discharge line 84 toward the final gas discharge line 61, and the aforementioned circulation loop is formed.

[0161] The hydrogen-containing gas, after merging from the hydrogen gas discharge line 84 into the final gas discharge line 61, is circulated and supplied to the negative electrode of the polymer electrolyte fuel cell 81 by the hydrogen gas supply pump 79, together with the secondary purified gas supplied from the final gas discharge line 61, and reused for power generation. Here, the pressure regulator 85 is a device that adjusts the pressure of the hydrogen-containing gas discharged from the polymer electrolyte fuel cell 81. When power is generated by the polymer electrolyte fuel cell (PEFC) 81, the pressure regulator 85 maintains the pressure of the secondary purified gas at the negative electrode under a constant pressure of several hundred kPa (for example, 200 to 900 kPa). Due to the effect of the circulation loop at that time, the amount of secondary purified gas supplied to the negative electrode per unit time is kept sufficiently in excess of the amount of secondary purified gas consumed per unit time required to obtain the output current of the polymer electrolyte fuel cell 81. Furthermore, it maintains the pressure balance with the air pressure supplied to the positive electrode side via the electrolyte membrane, and also contributes to adjusting the amount of moisture in the negative electrode. The pressure regulator 85 uses a pressure regulating valve to maintain a constant primary pressure upstream of the pressure regulator 85. Furthermore, most of the water generated at the positive electrode during power generation in the polymer electrolyte fuel cell (PEFC) is discharged from the air outlet on the positive electrode side, along with the oxygen and nitrogen gases in the air that were not consumed at the positive electrode.

[0162] In the normal operating state of the fuel cell system C1 shown in Figure 10, as described above, the hydrogen-containing gas flow path switched by the flow path switch 86 is maintained in the direction from the hydrogen gas discharge line 84 to the final gas discharge line 61, thereby forming the aforementioned hydrogen gas circulation loop. At this time, a stable high output can be obtained for a while after the start of power generation by the polymer electrolyte fuel cell (PEFC) 81. However, the secondary purified gas that permeates the separation membrane of the secondary purification section and is supplied to the polymer electrolyte fuel cell 81 via the final gas discharge line 61 and the hydrogen gas supply line 83 contains a small amount of nitrogen gas, about 2-5 volume%, along with the main component, hydrogen gas. Therefore, during power generation by the polymer electrolyte fuel cell 81, the secondary purified gas containing nitrogen gas is supplied and continues to be circulated to the polymer electrolyte fuel cell 81 through the hydrogen gas discharge line 84, etc. During this time, only hydrogen gas is consumed as fuel at the negative electrode of the polymer electrolyte fuel cell 81, so within the aforementioned circulation loop, the nitrogen gas concentration gradually increases from an initial concentration of about 2-5 volume%. Such increases in nitrogen gas concentration can increase concentration polarization at the negative electrode of the polymer electrolyte fuel cell 81, potentially reducing power generation efficiency. Therefore, it is necessary to reduce the nitrogen gas concentration in the circulation loop until the effect reaches an unacceptable level.

[0163] In the fuel cell system C1, as described above, the hydrogen gas discharge line 84 is equipped with a flow path switch 86, and a hydrogen gas treatment line 87 is provided, which branches off from the hydrogen gas discharge line 84 via the flow path switch 86 and discharges the hydrogen-containing gas to the outside. Before the nitrogen gas concentration increases as described above and the decrease in power generation efficiency exceeds an acceptable level, the flow path of the hydrogen-containing gas is switched by the flow path switch 86 so that the direction of the hydrogen-containing gas is toward the hydrogen gas treatment line 87, thereby allowing the nitrogen-concentrated gas that had been staying in the circulation loop to be discharged from the system as hydrogen-containing gas by the hydrogen gas supply pump 79. When the discharge of the hydrogen-containing gas staying in the circulation loop to the outside is completed and the gas in the circulation loop is completely replaced by the secondary purified gas supplied by the supply pump 79, the nitrogen gas concentration in the hydrogen-containing gas staying in the circulation loop returns to approximately its initial state (e.g., 2-5 volume%). At that point, the direction toward which the hydrogen-containing gas that was switched by the flow path switch 86 is toward the normal final gas discharge line 61. During the series of processes described above, it is possible to continue generating power with the polymer electrolyte fuel cell 81. With the configuration of the fuel cell system C1 described above, which intermittently discharges the nitrogen-enriched gas from the system, the nitrogen gas concentration that has risen in the circulation loop can be restored to its initial state (e.g., 2-5 volume%), preventing an increase in concentration polarization at the negative electrode of the polymer electrolyte fuel cell 81 and a decrease in power generation efficiency, thereby maintaining stable, high-output power generation.

[0164] In the above configuration, the hydrogen-containing gas discharged from the hydrogen gas treatment line 87 still contains a high concentration of hydrogen gas and is flammable. Therefore, when discharging, it is preferable to take fire prevention measures, such as mixing the hydrogen-containing gas with a large amount of air in a situation where fire, static electricity, etc., are sufficiently eliminated, and then discharging it outside the system. Furthermore, it is preferable to provide, for example, a flame arrestor to prevent flashback at the end of the piping that is ultimately discharged outside the system. Alternatively, the hydrogen-containing gas discharged from the hydrogen gas treatment line 87 can be guided to the combustor 29 of the hydrogen gas production device A or hydrogen gas supply device B in the fuel cell system C1 (the piping system for this is not shown), and burned together with the residual gas and air introduced into the combustor 29 for treatment.

[0165] The configuration of fuel cell system C1, which intermittently discharges concentrated nitrogen gas from the system, is similar to the method disclosed in Patent Document 2, which intermittently purges nitrogen gas accumulated at the negative electrode during power generation in a polymer electrolyte fuel cell. However, while the initial concentration of nitrogen gas in the fuel gas supplied to the polymer electrolyte fuel cell is high at approximately 25 volume% in Patent Document 2, it is much lower in the fuel cell system C1 of the present invention, for example, at 2-5 volume%. Therefore, the concentration polarization at the negative electrode during normal operation is suppressed compared to Patent Document 2, resulting in higher power efficiency. Furthermore, in fuel cell system C1, the initial concentration of nitrogen gas is low, and the frequency of the above-mentioned discharge required to restore the nitrogen gas concentration is less than in Patent Document 2. As a result, the amount of hydrogen gas lost due to discharge from the system is significantly less than in Patent Document 2. Furthermore, in the fuel cell systems C3 to C7 shown in Figures 12 to 17, examples are shown in which a configuration similar to that of fuel cell system C1 is provided, in which concentrated nitrogen gas is intermittently discharged from the system.

[0166] Figure 11 shows a fuel cell system C2 that prevents an increase in concentration polarization and a decrease in power generation efficiency at the negative electrode of a polymer electrolyte fuel cell 81, and maintains stable, high-output power generation. Since the fuel cell system C2 utilizes the separation membrane of the hydrogen separation section 19 after the removal of residual ammonia gas, it is preferable that the hydrogen gas production device A or hydrogen gas supply device B in the fuel cell system C2 has an ammonia adsorption section as a primary purification section 15 and a hydrogen separation section 19 as a secondary purification section. In the fuel cell system C2, instead of the configuration of the fuel cell system C1 in which nitrogen gas is concentrated and gas is intermittently discharged outside the system, a hydrogen gas treatment line 87 is provided that branches off from the hydrogen gas discharge line 84 via a flow path switch 86 and joins the secondary purification gas line 21 upstream of the separation membrane of the secondary purification section 19 (hydrogen separation section). For example, a three-way valve can be used as the flow path switch 86. The hydrogen gas processing line 87 is equipped with a reflux pump 88, and further, a pressure regulating valve 89 and a check valve 90 are provided in the section just before it joins the secondary purified gas line 21.

[0167] In fuel cell system C2, before the nitrogen gas concentration increases as described above and the decrease in power generation efficiency exceeds an acceptable level, the flow path is switched by the flow path switch 86 so that the direction in which the hydrogen-containing gas is discharged is towards the hydrogen gas treatment line 87, and the reflux pump 88 is started. The hydrogen-containing gas, which has been concentrated with nitrogen gas and has been staying in the circulation loop, is pressurized by the reflux pump 88 and, after passing through the hydrogen gas treatment line 87, merges with the primary purified gas passing through the primary purified gas line 17 upstream of the separation membrane in the hydrogen separation unit 19. In the portion of the hydrogen gas treatment line 87 just before the merger, the pressure of the hydrogen-containing gas, which has been concentrated with nitrogen gas in the hydrogen gas treatment line 87, is adjusted by the pressure regulating valve 89 so that it is equal to the pressure of the primary purified gas in the primary purified gas line. This pressure regulation prevents the hydrogen-containing gas from flowing upstream of the primary purified gas line 17 and prevents the primary purified gas from flowing into the hydrogen gas treatment line 87. Subsequently, the hydrogen-containing gas, with nitrogen gas concentrated in it, is supplied to the polymer electrolyte fuel cell 81 as fuel gas via the supply pump 79, after the nitrogen gas contained in each gas is separated by a separation membrane (at which point the primary purified gas becomes secondary purified gas, from which the nitrogen gas has been separated). This fuel gas is then transported via the final gas discharge line 61 and the hydrogen gas supply line 83. In this process, the flow rate per unit time of the hydrogen-containing gas with nitrogen gas concentrated in it, transported by the reflux pump 88, must be limited to such an extent that it does not exceed the separation processing capacity of the separation membrane at the time of merging.

[0168] When the gas in the circulation loop is completely replaced by the secondary purified gas and the hydrogen-containing gas from which nitrogen gas has been removed, supplied by the supply pump 79, the nitrogen gas concentration in the gas remaining in the circulation loop returns to approximately its initial state (e.g., 2-5 volume%), the direction toward which the hydrogen-containing gas is directed, switched by the flow path switch 68, returns to the normal final gas discharge line 61 side, and the reflux pump 88 is stopped. At this point, the check valve 90 prevents the inflow of primary purified gas into the hydrogen gas treatment line 87, which would result in a pressure drop in the hydrogen gas treatment line 87 after the reflux pump 88 has stopped.

[0169] During the series of processes described above, it is possible to continue generating power with the polymer electrolyte fuel cell 81. With the configuration of the fuel cell system C2 described above, the nitrogen gas concentration that has risen in the circulation loop can be restored to its initial state (e.g., 2-5 volume%), preventing an increase in concentration polarization and a decrease in power generation efficiency at the negative electrode of the polymer electrolyte fuel cell 81, and maintaining stable, high-output power generation.

[0170] While fuel cell system C2 has a slightly more complex configuration than fuel cell system C1, it has the advantage of being able to reduce the amount of hydrogen gas lost due to emissions outside the system to almost zero by using only the equipment within fuel cell system C2. The same configuration as fuel cell system C2, which removes nitrogen gas from the nitrogen-enriched gas, can also be applied to fuel cell systems C3 to C7 shown in Figures 12 to 17, replacing the same configuration as fuel cell system C1, which intermittently discharges the nitrogen-enriched gas outside the system.

[0171] Furthermore, in order to reduce the dead volume that is difficult to discharge when discharging gases that remain in the circulation loop of fuel cell systems C1 and C2, it is preferable that the length of the piping between the confluence of the hydrogen gas discharge line 84 and the final gas discharge line 61 and the flow path switch 86 be as short as possible.

[0172] Next, we will explain the timing at which, in the fuel cell systems C1 and C2 described above, the flow path is switched by the flow path switcher 86 from the state in which a circulating loop is formed during normal operation (in fuel cell system C2, the reflux pump 88 is started at the same time), and the timing at which the nitrogen gas in the circulating loop moves to the processing of concentrated gas (hereinafter referred to as the "processing start time"), and the timing at which the processing is completed and the flow path is switched back to the original state by the flow path switcher 86 (in fuel cell system C2, the reflux pump 88 is stopped at the same time; hereinafter referred to as the "processing end time").

[0173] In fuel cell systems C1 and C2, during power generation, from the moment the flow path switch 86 is set so that the direction of the hydrogen-containing gas flows from the hydrogen gas processing line 87 to the final gas discharge line 61 (this is when a circulating loop is formed, and is therefore hereafter referred to as the "circulating loop formation point"), the concentration of nitrogen gas in the gas remaining in the circulating loop gradually increases from the initial state (e.g., 2-5 volume%) as power generation progresses. This increase in nitrogen gas concentration in the circulating loop causes an increase in the concentration polarization of hydrogen gas at the negative electrode of the polymer electrolyte fuel cell 81, reducing power generation efficiency. The point at which this decrease in power generation efficiency reaches an unacceptable level is the "processing start point". This "unacceptable level" is arbitrary and is assumed as appropriate depending on the target and purpose of the power generation supply. The nitrogen gas concentration in the circulating loop when the power generation efficiency decreases to the assumed "unacceptable level" is the upper limit of the acceptable nitrogen gas concentration, and the "processing start point" is the point at which the nitrogen gas concentration in the circulating loop reaches this upper limit of the acceptable nitrogen gas concentration.

[0174] The nitrogen gas concentration in the circulating loop can be actually monitored by installing a predetermined concentration detection means within the circulating loop, but it is preferable to use an indicator that can be detected more easily. Hereinafter, the nitrogen gas concentration in the circulating loop at a certain point in time after the circulating loop formation during power generation is a function of the volume within the circulating loop (including the gas phase volume of the negative electrode of the polymer electrolyte fuel cell 81), the initial nitrogen gas concentration in the circulating loop (approximated by the nitrogen gas concentration in the secondary purified gas supplied as fuel, for example, 2-5 volume%), and the amount of electricity generated by the polymer electrolyte fuel cell 81 from the time of circulating loop formation to that point. Of these, the volume within the circulating loop and the initial nitrogen gas concentration in the circulating loop are default values ​​for fuel cell systems C1 and C2 and are constants. Furthermore, the output current of the polymer electrolyte fuel cell 81 is generally a value preset as a power generation condition and is constantly monitored. Therefore, the amount of electricity generated by the polymer electrolyte fuel cell 81 can also be easily and constantly monitored as the integral value of the output current over time. From the above, the nitrogen gas concentration in the circulating loop is a function of the amount of electricity generated and the elapsed time since the circulating loop was formed, and both can be easily monitored at all times. Therefore, if the amount of electricity generated and the elapsed time since the circulating loop was formed are determined experimentally in advance as predetermined values ​​at the point when the decrease in power generation efficiency reaches an unacceptable level, these can be used as constantly monitorable indicators in place of the acceptable upper limit of nitrogen gas concentration. From the above, the "processing start time" in fuel cell systems C1 and C2 is detected as the point at which the flow path switcher 86 is set so that the direction of the hydrogen-containing gas moves from the final gas discharge line 61 side to the hydrogen gas processing line 87 side, and the amount of electricity generated or the elapsed time since the circulating loop was formed reaches the respective predetermined values ​​mentioned above. At this timing, the flow path can be switched by the flow path switcher 86.

[0175] As described above, at the "start of processing," the nitrogen gas concentration in the circulating loop can be roughly restored to its initial state (e.g., 2-5 volume%) by discharging the entire amount of gas that has reached the permissible upper limit of nitrogen gas concentration and is residing in the circulating loop, and by separating and removing the concentrated nitrogen gas in the entire amount using a separation membrane in fuel cell system C2. The "end of processing" is the point at which the above processing is completed. The mass of gas that has reached the permissible upper limit of nitrogen gas concentration and is residing in the circulating loop at the "start of processing" can be roughly calculated using the following equation 4. Formula 4: (Mass [kg] of gas with the permissible upper limit of nitrogen gas concentration remaining in the circulation loop) ≈(Circulation loop volume [m³) 3 ]) × (Gas density at the pressure and temperature inside the circulation loop [kg / m³ 3 ]) ≈(Circulation loop volume [m³) 3 ]) × (Nitrogen gas density at the pressure and temperature inside the circulation loop [kg / m³ 3 ])

[0176] In the right-hand side of Equation 4, "gas density at the internal pressure and temperature of the circulation loop" is the density of the nitrogen gas at the upper limit of the allowable nitrogen gas concentration at the internal pressure and temperature of the circulation loop. Since nitrogen gas has a density more than an order of magnitude greater than hydrogen gas, for example, when the nitrogen gas concentration rises to 20-30 volume%, the contribution of nitrogen gas density becomes dominant in that gas density. For this reason, although the actual value of the upper limit of the allowable nitrogen gas concentration is unknown, we assume here that it is approximated by the density of pure nitrogen gas. Furthermore, the nitrogen gas density at the internal pressure and temperature of the circulation loop can be calculated using the following Equation 5.

[0177] Formula 5: (Nitrogen gas density at the pressure and temperature inside the circulation loop [kg / m³] 3 ]) =(Nitrogen gas density at standard conditions of 0.1013 MPa and 0°C: 1.250 [kg / m³] 3 ]) × 273.2 / (273.2 + temperature in the circulation loop [°C]) × (Circulation loop pressure [MPa]) / (0.1013 [MPa])

[0178] In Equation 5, the pressure inside the circulating loop can be approximated by the primary pressure of the pressure regulator 85. The temperature inside the circulating loop can be approximated by the temperature inside the polymer electrolyte fuel cell, which is commonly monitored. Therefore, from Equations 4 and 5, an approximate value of the mass of gas at the permissible upper limit of nitrogen gas concentration remaining in the circulating loop can be calculated. In fuel cell systems C1 and C2, when processing hydrogen-containing gas containing nitrogen gas at the permissible upper limit of nitrogen gas concentration remaining in the circulating loop, the mass flow rate of the gas per unit time in the hydrogen gas processing line 87 can be measured by, for example, installing a mass flow meter (not shown). It is estimated that if the above processing is performed for a time obtained by dividing, for example twice the mass of the gas at the permissible upper limit of nitrogen gas concentration remaining in the circulating loop, estimated by Equations 4 and 5, by the measured mass flow rate per unit time, the processing will be approximately complete. This can be considered the "processing completion point," and at this timing, the flow path can be switched again by the flow path switcher 86.

[0179] As an external load 91, in addition to the DC motor for propulsion of the mobile body described later, lighting, various electrical equipment, etc. that receive DC power input, or motors, lighting, various electrical equipment, etc. that receive AC power input via an inverter can be used, and these can be driven by the power generated by the polymer electrolyte fuel cell (PEFC) 81. Furthermore, a secondary battery can be used as an external load 91, and by charging it, the power generated by the polymer electrolyte fuel cell (PEFC) can be stored. That is, a portion of the power charged in the secondary battery can be used as a power source to drive various devices such as electric heaters 5a, 7a, 7b, 35, etc., electrically operated coolers, various valves and switches, pressurizers and compressors 17a, 42, 65, etc., pressure reducers 22, various pressure regulators 18, 20, 24, etc., various measuring instruments (thermometers, pressure gauges, flow meters, etc.), and control and instrumentation equipment, which are provided in the hydrogen gas production device A or hydrogen gas supply device B that constitute the fuel cell system C. In such cases, various devices of hydrogen gas production device A or hydrogen gas supply device B are connected to the secondary battery via power distribution equipment, voltage adjustment equipment, etc., as needed (these are not shown in the diagram). In particular, when there is no external power supply in the installation environment of fuel cell system C, connecting the secondary battery as described above as an external load 91 is effective for starting and steady-state operation of hydrogen gas production device A or hydrogen gas supply device B. Fuel cell system C equipped with an external load 91 which is a secondary battery is also called a fuel cell system with energy storage function.

[0180] (Mobile) Next, the mobile body of the embodiment will be described. The mobile unit comprises the aforementioned fuel cell system C and a motor.

[0181] A motor is a device that generates power to propel a moving object by being driven by electricity generated by a polymer electrolyte fuel cell (PEFC). The motor is a load connected to the negative and positive electrodes of the fuel cell system C. Examples of motors used include rotary motors and the movable element of a linear motor. Preferably, the motor is connected to the negative and positive terminals of the polymer electrolyte fuel cell (PEFC) that constitutes the cell stack. When power is supplied from the polymer electrolyte fuel cell (PEFC), the motor is driven (for example, the rotating shaft of a rotary motor rotates, or the movable element moves linearly in a linear motor) to output mechanical power.

[0182] The mobile unit preferably further comprises a motor and a secondary battery connected to a polymer electrolyte fuel cell (PEFC). The secondary battery is connected in parallel to the motor and the polymer electrolyte fuel cell (PEFC), and a floating charge configuration is adopted that allows the motor to be driven by the polymer electrolyte fuel cell (PEFC) while the secondary battery is also charged (these are not shown in the figures). In other words, according to one embodiment, it is preferable to have a secondary battery connected in parallel to the polymer electrolyte fuel cell (PEFC) with the motor. This makes it possible to stabilize the power supplied to the motor even if the output of the polymer electrolyte fuel cell (PEFC) or the rotational speed of the motor fluctuates.

[0183] Mobile entities include, for example, airborne entities such as aircraft, helicopters, and drones; land-based entities such as vehicles (passenger cars, trucks, buses, etc.), railway vehicles, and cargo handling machinery; and water-based entities such as ships. Mobile entities are further equipped with a drive system that propels them by transmitting mechanical power output from a motor. The drive system is, for example, a propeller or rotor that propels the flight of airborne entities such as aircraft, helicopters, and drones; wheels or tracks that propel the movement of land-based entities such as vehicles (passenger cars, trucks, buses, etc.), railway vehicles, and cargo handling machinery; and a screw or water jet mechanism that propels the navigation of water-based entities such as ships.

[0184] The mobile unit may further include a tank (the high-pressure hydrogen tank described above) for storing at least a portion of the secondary purified gas discharged from the hydrogen gas production device A or the hydrogen gas supply device B.

[0185] The tank 1 of the fuel cell system C may, for example, be filled with liquefied ammonia as cargo or fuel for a mobile vehicle and mounted on the mobile vehicle.

[0186] (Method for producing hydrogen gas) Next, the hydrogen gas production method of the embodiment will be described. The hydrogen gas production method of this embodiment is a method of producing hydrogen gas by sequentially flowing ammonia gas, which is either the gas obtained by vaporizing liquefied ammonia or the boil-off gas of liquefied ammonia, decomposition gas obtained by decomposing ammonia gas, and purified gas obtained by purifying the decomposition gas, in one direction while flowing liquefied ammonia or boil-off gas of liquefied ammonia as a raw material.

[0187] The hydrogen gas production method comprises the following steps S1 to S4. • Heating step S1 involves heating at least the ammonia gas from liquefied ammonia and ammonia gas to raise the temperature of the ammonia gas to a temperature above the decomposition temperature. Step S2 involves decomposing ammonia gas heated to a decomposition temperature by contacting it with a catalyst to produce a decomposition gas containing hydrogen gas, nitrogen gas, and residual ammonia gas, which is then discharged downstream. • Primary purification step S3: Removes either residual ammonia gas or nitrogen gas from the decomposition gas to produce a primary purified gas, which is then discharged downstream. - Secondary purification step S4: Removing residual ammonia gas and the other nitrogen gas from the primary purified gas to produce secondary purified gas, which is then discharged downstream.

[0188] Of the primary purification step S3 and secondary purification step S4, the purification step that removes residual ammonia gas is an ammonia adsorption step in which residual ammonia gas is adsorbed onto an adsorbent. The purification step that removes nitrogen gas from the primary purification step S3 and the secondary purification step S4 is a hydrogen separation step that uses a separation membrane configured to separate the decomposed gas or primary purified gas into a permeate gas containing most of the hydrogen gas that has permeated the separation membrane and a residual gas containing the remainder of the hydrogen gas that remains on the upstream side of the separation membrane and nitrogen gas, by the differential pressure created between the upstream and downstream sides of the separation membrane, and then discharge the separated gas. In the heating step S1, during the start-up period from the start of hydrogen gas production until permeate gas exceeding a predetermined flow rate is discharged from the separation membrane, the liquefied ammonia or ammonia gas is heated using electricity by a first electric heater.

[0189] The hydrogen gas production method of the embodiment can be carried out using, for example, any of the above-described hydrogen gas production apparatus A, hydrogen gas supply apparatus B, fuel cell system C, or mobile unit.

[0190] According to the hydrogen gas production method of this embodiment, when producing hydrogen gas using ammonia as a raw material, the decomposition of ammonia at the start of hydrogen gas production can be carried out efficiently, nitrogen can be removed without using a high-pressure compressor, thereby reducing power consumption and making the equipment smaller and simpler.

[0191] Although the hydrogen gas production apparatus, hydrogen gas supply apparatus, fuel cell system, mobile unit, and hydrogen gas production method of the present invention have been described above, the present invention is not limited to the above embodiments, and various improvements and modifications may be made without departing from the spirit of the present invention. For example, when boil-off gas of liquefied ammonia is used as the raw material for hydrogen gas, hydrogen gas can be produced using a hydrogen gas production apparatus configured in the same way as hydrogen gas production apparatus A described above, with the boil-off gas flowing from a tank storing boil-off gas downstream from the raw material ammonia line 3. In this case, it is preferable to maintain the internal pressure in the tank storing boil-off gas at, for example, 1.4 to 1.6 MPa, so that the ammonia decomposition rate is kept high. [Explanation of Symbols]

[0192] 1 tank 1a Heater for keeping warm 3. Raw material ammonia line 3a Branch ammonia line 4. Supply valve 5. Vaporizer 5a Third electric heater 5b Low-temperature side flow path of the second heat exchanger (second heat exchange heater) 6 Flow regulator 7. Heater for raising the temperature 7a First electric heater 7b Second electric heater 7c Low-temperature side flow path of the first heat exchanger (first heat exchange heater) 8. Heating section for raising temperature 9. Ammonia decomposition section 11. Disassembly gas line 13 Cooler (1st cooler) 15. Primary purification section (ammonia adsorption section shown in figures other than Figure 4) 15A, 15B, 15X, 15Y Ammonia Adsorbent 15a Connection Line 17 Primary refining gas line 17a Pressurizer 18 Upstream pressure regulator 19. Secondary purification section (hydrogen separation section shown in figures other than Figure 4) 20 Downstream pressure regulator 21 Secondary Refining Gas Line 22 Pressure reducer 23 Residual gas discharge line 24 Nitrogen discharge pressure regulator 25 Second heat exchanger 27 Second cooler 28 Gas lines for regeneration 29 Combustor 30 branch gas lines 31 Combustion gas line 32. Outside air intake line 33 1st heat exchanger 35 Regeneration heater 37, 37A, 37B Inert gas introduction line 37c supply port 39, 39A, 39B Desorption Ammonia Discharge Line 41 Reliquefaction section 42 Compressor 43 Cooler 61 Final gas emission line 62 4th cooler 63 Refined gas tanks 65 Pressurizer 67 A pair of switching valves 67a, 67b, 67c valves 69 Third cooler 79. Purified gas supply pump 81 Solid polymer fuel cell 83. Purified gas supply line 84. Hydrogen-containing gas emission line 86. Flow path switch 87 Hydrogen-containing gas processing line 88 Reflux Pump 89 Pressure Regulating Valve 90 Check valve 91 External load

Claims

1. A hydrogen gas production apparatus that produces hydrogen gas by sequentially flowing in one direction ammonia gas, which is either the gas obtained by vaporizing the liquefied ammonia or the boil-off gas, a decomposition gas obtained by decomposing the ammonia gas, and purified gas obtained by purifying the decomposition gas, while flowing liquefied ammonia or the boil-off gas of the liquefied ammonia as a raw material, A heating unit that heats at least the ammonia gas from the liquefied ammonia and the ammonia gas to raise the ammonia gas to a temperature above the decomposition temperature, An ammonia decomposition unit that brings the ammonia gas, heated to the aforementioned decomposition temperature, into contact with a catalyst to decompose it, generating a decomposition gas containing hydrogen gas, nitrogen gas, and residual ammonia gas, and discharging it downstream, A primary purification unit is located downstream of the ammonia decomposition unit and removes either the residual ammonia gas or the nitrogen gas from the decomposition gas to produce a primary purified gas, which is then discharged downstream. The system includes a secondary purification unit located downstream of the primary purification unit, which removes the residual ammonia gas and the other of the nitrogen gas from the primary purified gas to produce a secondary purified gas, and discharges it downstream. The primary purification section and the secondary purification section from which the residual ammonia gas is removed is an ammonia adsorption section having an adsorbent for adsorbing the residual ammonia gas. The primary purification section and the secondary purification section from which the nitrogen gas is removed have a separation membrane, and the separation membrane is configured to separate the decomposition gas or the primary purified gas into a permeate gas containing most of the hydrogen gas that has permeated the separation membrane and a residual gas containing the remaining hydrogen gas and nitrogen gas that remains upstream of the separation membrane without permeating the membrane, and to discharge the separated gas, by the differential pressure created between the upstream and downstream sides of the separation membrane. The heating unit for raising the temperature has a first electric heater that heats the liquefied ammonia or ammonia gas using electricity, and the hydrogen gas production apparatus heats the liquefied ammonia or ammonia gas with the first electric heater during the start-up period from the start of operation of the hydrogen gas production apparatus until the permeate gas exceeding a predetermined flow rate is discharged from the hydrogen separation unit.

2. The heating unit for raising the temperature further comprises a combustor that burns the residual gas discharged from the hydrogen separation unit together with air and discharges the combustion gas, and a first heat exchange heater that heats the ammonia gas by heat exchange with the combustion gas discharged from the combustor. The hydrogen gas production apparatus according to claim 1, wherein the ammonia gas is heated by the first heat exchange heater during a steady-state operation period that begins when the permeate gas exceeding a predetermined flow rate is discharged from the hydrogen separation unit.

3. The hydrogen gas production apparatus according to claim 2, wherein the heating unit for raising the temperature reduces the output of the first electric heater continuously or in stages after the start of the steady-state operation period.

4. The first electric heater heats the liquefied ammonia or ammonia gas flowing upstream of the ammonia decomposition section. The hydrogen gas production apparatus according to claim 2, wherein the heating unit for raising the temperature further includes a second electric heater that uses electricity to adjust the temperature of the ammonia gas flowing through the ammonia decomposition unit.

5. The hydrogen gas production apparatus according to claim 4, wherein the heating unit for raising the temperature stops heating the liquefied ammonia or ammonia gas by the first electric heater during the steady-state operation period, and then heats the ammonia gas by the first heat exchange heater and the second electric heater.

6. The heating unit for raising the temperature further comprises a second heat exchange heater that vaporizes the liquefied ammonia by heat exchange with the decomposition gas, and a third electric heater that heats the liquefied ammonia using electricity. The hydrogen gas production apparatus according to claim 1, wherein the first electric heater heats the gas obtained by vaporizing the liquefied ammonia.

7. The hydrogen gas production apparatus according to claim 6, wherein the heating unit for raising the temperature heats the liquefied ammonia with the third electric heater during the period from the start of operation of the hydrogen gas production apparatus until the decomposition gas exceeding a predetermined flow rate is discharged from the ammonia decomposition unit.

8. The hydrogen gas production apparatus according to claim 7, wherein the liquefied ammonia is heated by the second heat exchange heater during a period that begins when the decomposition gas exceeding a predetermined flow rate is discharged from the ammonia decomposition unit.

9. The hydrogen gas production apparatus according to claim 8, wherein the heating unit for raising the temperature reduces the output of the third electric heater continuously or in stages after the start of the period which begins when the decomposition gas exceeding a predetermined flow rate is discharged from the ammonia decomposition unit.

10. The heating unit for raising the temperature further comprises a combustor that burns the residual gas discharged from the hydrogen separation unit together with air and discharges the combustion gas, and a first heat exchange heater that heats the ammonia gas by heat exchange with the combustion gas discharged from the combustor. The hydrogen gas production apparatus according to claim 1 or 2, wherein the combustor burns at least one of the ammonia gas extracted upstream of the ammonia decomposition unit and the decomposition gas or the purified gas extracted downstream of either the ammonia decomposition unit or the ammonia decomposition unit together with the residual gas.

11. The hydrogen gas production apparatus according to claim 1 or 2, wherein the permeate gas contains 70 to 80 volume percent of the hydrogen gas in the primary purified gas.

12. The hydrogen gas production apparatus according to claim 2 or 3, wherein the residual gas discharged from the hydrogen separation unit is guided to the combustor without passing through the ammonia adsorption unit.

13. The hydrogen gas production apparatus according to claim 2 or 3, wherein the residual gas discharged from the hydrogen separation unit is guided to the combustor without being heated.

14. The ammonia adsorption section is A plurality of upstream ammonia adsorbents arranged in parallel in the aforementioned one direction, It comprises at least one upstream ammonia adsorbent and at least one downstream ammonia adsorbent arranged in series in one direction, The hydrogen gas production apparatus according to claim 1 or 2, wherein each of the ammonia adsorbents has the adsorbent.

15. The separation membrane is made of polymer or ceramic. The hydrogen gas production apparatus according to claim 1 or 2, wherein the differential pressure is 0.3 to 0.9 MPa.

16. The ammonia adsorption unit comprises a regeneration heater for heating the adsorbent that has adsorbed the residual ammonia gas, and an inert gas introduction line for introducing an inert gas from the outside, wherein the residual ammonia gas adsorbed on the adsorbent is detached from the adsorbent by heating with the regeneration heater and discharged together with the inert gas introduced through the inert gas introduction line, as described in claim 1 or 2.

17. A hydrogen gas production apparatus according to claim 1, A hydrogen gas supply device comprising a purified gas tank for storing the secondary purified gas produced in the hydrogen gas production apparatus.

18. A hydrogen gas production apparatus according to claim 1, or a hydrogen gas supply apparatus according to claim 17, A fuel cell system comprising a polymer electrolyte fuel cell having a negative electrode and a positive electrode, wherein the negative electrode and the positive electrode are connected to an external load, and the system is configured to generate electricity by supplying a secondary purified gas produced in the hydrogen gas production device or the hydrogen gas supply device to the negative electrode and air to the positive electrode.

19. It is a mobile object, The fuel cell system according to claim 18, A mobile body comprising: a motor connected to the negative and positive electrodes of a polymer electrolyte fuel cell in the fuel cell system, which is driven by electricity generated by the fuel cell in the fuel cell system and generates power to propel the mobile body.

20. The mobile body according to claim 19, further comprising a secondary battery connected in parallel with the motor to the polymer electrolyte fuel cell.

21. A method for producing hydrogen gas, comprising sequentially flowing liquefied ammonia or the boil-off gas of liquefied ammonia as a raw material, ammonia gas which is either the gas obtained by vaporizing the liquefied ammonia or the boil-off gas, a decomposition gas obtained by decomposing the ammonia gas, and a purified gas obtained by purifying the decomposition gas in one direction, A heating step in which at least the ammonia gas is heated from the liquefied ammonia and the ammonia gas, and the ammonia gas is heated to a temperature above the decomposition temperature, The ammonia decomposition step involves bringing the ammonia gas, heated to the aforementioned decomposition temperature, into contact with a catalyst to decompose it, generating a decomposition gas containing hydrogen gas, nitrogen gas, and residual ammonia gas, and discharging it downstream. A primary purification step involves removing either the residual ammonia gas or the nitrogen gas from the decomposition gas to produce a primary purified gas, which is then discharged downstream. The system includes a secondary purification step of removing the residual ammonia gas and the other of the nitrogen gas from the primary purified gas to produce a secondary purified gas, which is then discharged downstream. The purification step among the primary and secondary purification steps that removes the residual ammonia gas is an ammonia adsorption step in which the residual ammonia gas is adsorbed onto an adsorbent. The primary purification step and the secondary purification step, which removes the nitrogen gas, is a hydrogen separation step that uses a separation membrane configured to separate the decomposition gas or the primary purified gas into a permeate gas containing most of the hydrogen gas that has permeated the separation membrane and a residual gas containing the remainder of the hydrogen gas and the nitrogen gas that remains on the upstream side of the separation membrane without permeating the separation membrane, and then discharge the separated gas, by the differential pressure created between the upstream and downstream sides of the separation membrane. A method for producing hydrogen gas, wherein in the heating step, during the start-up period from the start of hydrogen gas production until the permeate gas exceeding a predetermined flow rate is discharged from the separation membrane, the liquefied ammonia or ammonia gas is heated using electricity by a first electric heater.

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