Hydrogen supply system

Abstract

A hydrogen supply system (100) includes a hydrogen production unit (101) which produces hydrogen, a hydrogen boosting unit (102) which boosts a pressure of the hydrogen produced by the hydrogen production unit (101) to a pressure at which the hydrogen can be supplied to a gas grid, a grid gas lead-in unit (103) which leads grid gas from the gas grid (901), a hydrogen concentration adjustment unit (104) which adjusts a mixed gas to have a hydrogen concentration equal to or lower than an allowable hydrogen concentration specified in the gas grid (901), and a mixed gas return unit (105) which supplies the mixed gas to the gas grid.

Description

Technical Field

[0001] The present invention relates to a hydrogen supply system capable of supplying hydrogen at equal to or lower than a hydrogen concentration specified in a gas grid when hydrogen is supplied to the gas grid in which mixing of hydrogen is allowed.Background Art

[0002] Hydrogen as opposed to fossil fuels is clean energy that does not emit carbon dioxide during combustion. Thus, attention has been paid as one of clean energy for countermeasures against global warming, and technological development related to production, transportation, and utilization of hydrogen has been advanced.

[0003] Under such circumstances, it has been proposed to supply hydrogen produced by electrolysis of water using renewable energy, or the like, reforming of natural gas, or the like, to a gas pipeline in which mixing of hydrogen is allowed. In this case, it is assumed that a hydrogen concentration becomes equal to or higher than a hydrogen concentration specified in a gas grid in the vicinity of a hydrogen supply point, and an amount of hydrogen desired to be supplied cannot be supplied.

[0004] In addition, in order to supply hydrogen to a gas grid, PTL 1 below proposes a method of mixing hydrogen with fossil fuel gas such as LP gas or natural gas so as to satisfy city gas standards and supplying the mixture to the gas grid. PTL 2 discloses systems and methods for distributing hydrogen. A fuel is supplied in a pipe, and a stream comprising hydrogen is injected into the pipe. Hydrogen is extracted from the pipe downstream of the injection point.Citation ListPatent Literature

[0005] PTL 1: JP 2006-169357 A PTL 2: US 2004 / 112427 A1 Summary of InventionTechnical Problem

[0006] In the invention described in PTL 1, fossil fuel gas is newly mixed in order to supply hydrogen. Thus, in the invention described in PTL 1, supply cost is greatly increased.

[0007] It is therefore an object of the present invention to prevent increase in cost and prevent a hydrogen concentration from exceeding a hydrogen concentration specified value provided in a gas grid when supplying hydrogen produced as clean energy to the gas grid.Solution to Problem

[0008] In order to solve the above problems, a hydrogen supply system of the present invention is set forth in claim 1.

[0009] Other means will be described in description of embodiments.Advantageous Effects of Invention

[0010] According to the present invention, it is possible to supply hydrogen while preventing increase in cost and preventing a hydrogen concentration from exceeding a hydrogen concentration specified value provided in a gas grid when supplying hydrogen produced as clean energy to the gas grid.Brief Description of Drawings

[0011] [FIG. 1] FIG. 1 is an explanatory diagram of a hydrogen supply system for explaining a first embodiment. [FIG. 2] FIG. 2 is an explanatory diagram of a hydrogen supply system for explaining a second embodiment. [FIG. 3] FIG. 3 is an explanatory diagram of a hydrogen supply system for explaining a third embodiment. [FIG. 4] FIG. 4 is an explanatory diagram of a hydrogen supply system for explaining a fourth embodiment. Description of Embodiments

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the same components are denoted by the same reference numerals, and in a case where description thereof overlaps, the description thereof may be omitted. In addition, the present invention is not limited to the following embodiments.<<First embodiment>>

[0013] FIG. 1 is an explanatory diagram for explaining a hydrogen supply system 100 according to a first embodiment.

[0014] The hydrogen supply system 100 described in the first embodiment includes a hydrogen production unit 101, a hydrogen boosting unit 102, a grid gas lead-in unit 103, a hydrogen concentration adjustment unit 104, and a mixed gas return unit 105. The hydrogen supply system 100 is connected to a gas grid 901 to supply hydrogen to the gas grid 901. At least blend gas of natural gas and hydrogen flows through the gas grid 901. The blend gas may be referred to as mixed gas.

[0015] The hydrogen production unit 101 produces hydrogen. The hydrogen boosting unit 102 boosts a pressure of the hydrogen produced by the hydrogen production unit 101 to a pressure at which the hydrogen can be supplied to the gas grid 901 and supplies the hydrogen to the hydrogen concentration adjustment unit 104. The grid gas lead-in unit 103 leads grid gas from the gas grid 901 and supplies the grid gas to the hydrogen concentration adjustment unit 104. The hydrogen concentration adjustment unit 104 adjusts the mixed gas to have a hydrogen concentration equal to or lower than an allowable hydrogen concentration specified in the gas grid 901. The mixed gas return unit 105 supplies the mixed gas adjusted by the hydrogen concentration adjustment unit 104 to the gas grid 901.

[0016] Here, the grid gas lead-in unit 103 and the mixed gas return unit 105 are connected to the gas grid 901. In the gas grid 901, for example, mixed gas (grid gas) of natural gas and hydrogen such as city gas exists. In the gas grid 901, an upper limit value of the hydrogen concentration is provided from the viewpoint of preventing gas grid hydrogen embrittlement and in order to use an existing natural gas utilization facility.

[0017] The hydrogen production unit 101 produces hydrogen 2 to be supplied to the gas grid 901. Here, while a production flow rate of the hydrogen 2 to be produced may be determined through prediction from hydrogen demand, or the hydrogen 2 may be produced at a hydrogen amount instructed by a gas grid manager, both of them are preferably determined in consideration of the hydrogen demand. Here, examples of a method for producing hydrogen by the hydrogen production unit 101 include a method of producing hydrogen by electrolysis of water using electric power generated by renewable energy such as solar power generation and wind power generation, a method of producing hydrogen by causing carbon monoxide generated when coal is gasified to undergo shift reaction and then separating carbon dioxide, a method of producing hydrogen by steam reforming of natural gas, and the like, but are not limited to any of these. In order to achieve carbon free, in a case where carbon dioxide is generated in a production process, it is preferable to collect carbon dioxide and convert the carbon dioxide into valuable materials or store the carbon dioxide.

[0018] A pressure of the hydrogen 2 produced by the hydrogen production unit 101 is boosted to a pressure that can be supplied to the gas grid 901 by the hydrogen boosting unit 102. The pressure that can be supplied to the gas grid 901 varies depending on a location of the gas grid 901 to which hydrogen is to be supplied, and is from 0 to 0.1 MPaG in a low pressure gas grid, from 0.1 to 1.0 MPaG in an intermediate pressure gas grid, equal to or higher than 1.0 MPaG in a high pressure gas grid, and the like, and is changed depending on a point where hydrogen is to be supplied.

[0019] After the pressure of the hydrogen 2 is boosted, the hydrogen 2 is supplied to the hydrogen concentration adjustment unit 104. The grid gas lead-in unit 103 connected to the gas grid 901 supplies the grid gas 1 existing in the gas grid 901 to the hydrogen concentration adjustment unit 104.

[0020] Next, when the grid gas 1 and the hydrogen 2 are supplied, the hydrogen concentration adjustment unit 104 mixes these two kinds of gas to obtain mixed gas 3. Here, the hydrogen concentration adjustment unit 104 adjusts a hydrogen concentration of the mixed gas by changing a grid gas flow rate so as not to exceed the upper limit value of the hydrogen concentration specified in the gas grid 901. Here, the upper limit value of the hydrogen concentration specified in the gas grid 901 is also referred to as an allowable hydrogen concentration. The reason why the grid gas flow rate is changed is that the hydrogen production unit 101 needs to supply an amount in consideration of hydrogen demand.

[0021] The mixed gas 3 adjusted by the hydrogen concentration adjustment unit 104 is supplied to the gas grid 901 through the mixed gas return unit 105.

[0022] According to the hydrogen supply system 100 of the present embodiment, it is possible to supply produced hydrogen at a hydrogen concentration equal to or lower than a specified value provided in the gas grid 901.<<Second embodiment>>

[0023] In a second embodiment, an example of a method of operating the grid gas lead-in unit 103 which is one of the components of the hydrogen supply system 100 of the present invention will be described. FIG. 2 illustrates a configuration diagram of the hydrogen supply system 100 in which components of the grid gas lead-in unit 103 are illustrated in detail.

[0024] As illustrated in FIG. 2, the grid gas lead-in unit 103 includes a grid gas hydrogen concentration measurement unit 1031, a grid gas hydrogen concentration communication unit 1032, a grid gas flow rate reception unit 1033, a grid gas flow rate adjustment unit 1034, and a grid gas supply unit 1035, and is connected to the hydrogen concentration adjustment unit 104 in the hydrogen supply system 100 and the gas grid 901.

[0025] The grid gas hydrogen concentration measurement unit 1031 measures the hydrogen concentration in the grid gas. The grid gas hydrogen concentration communication unit 1032 transmits data of the hydrogen concentration in the grid gas to the hydrogen concentration adjustment unit 104. The grid gas flow rate reception unit 1033 receives the grid gas flow rate calculated by the hydrogen concentration adjustment unit 104. The grid gas flow rate adjustment unit 1034 adjusts and leads the grid gas. The grid gas supply unit 1035 supplies the grid gas to the hydrogen concentration adjustment unit 104.

[0026] First, the grid gas hydrogen concentration measurement unit 1031 measures the hydrogen concentration in the grid gas. The grid gas hydrogen concentration communication unit 1032 transmits the measured grid gas hydrogen concentration data 201 to the hydrogen concentration adjustment unit 104. Here, the grid gas hydrogen concentration data 201 is used to determine the grid gas flow rate. A measurement interval in the grid gas hydrogen concentration measurement unit 1031 and a communication interval in the grid gas hydrogen concentration communication unit 1032 are not limited, but are preferably set to equal to or less than 5 minutes in consideration of coping with fluctuation of the hydrogen concentration in the grid gas.

[0027] Next, the hydrogen concentration adjustment unit 104 determines the grid gas flow rate that achieves the hydrogen concentration specified in the gas grid 901 from the grid gas hydrogen concentration data 201 and the produced hydrogen amount. Grid gas flow rate command data 202 determined by the hydrogen concentration adjustment unit 104 is transmitted to the grid gas flow rate reception unit 1033 by a grid gas flow rate command unit 1044. The grid gas flow rate adjustment unit 1034 adjusts the flow rate of the grid gas on the basis of the grid gas flow rate command data 202 received by the grid gas flow rate reception unit 1033.

[0028] Here, a method for calculating the grid gas flow rate by the hydrogen concentration adjustment unit 104 will be described in the third embodiment. Similarly to the communication interval of the grid gas hydrogen concentration communication unit 1032, an interval at which the grid gas flow rate reception unit 1033 receives data is preferably set to equal to or less than 5 minutes.

[0029] The grid gas flow rate adjustment unit 1034 adjusts the grid gas flow rate to be led from the gas grid 901 to a value of the grid gas flow rate command data 202 received by the grid gas flow rate reception unit 1033. The grid gas supply unit 1035 supplies the grid gas 1 to the hydrogen concentration adjustment unit 104. Thereafter, as described in the first embodiment, the hydrogen concentration adjustment unit 104 mixes the grid gas 1 and the hydrogen 2 produced by the hydrogen production unit 101. The mixed gas 3 adjusted by the hydrogen concentration adjustment unit 104 is supplied to the gas grid 901 through the mixed gas return unit 105.

[0030] According to the hydrogen supply system 100 including the grid gas lead-in unit 103 of the present embodiment, even in a case where the hydrogen concentration in the grid gas fluctuates, the hydrogen concentration in the mixed gas adjusted by the hydrogen concentration adjustment unit 104 can be made equal to or less than the specified value of the gas grid 901.<<Third embodiment>>

[0031] In a third embodiment, an example of a method for operating the hydrogen concentration adjustment unit 104 which is one of the components of the hydrogen supply system 100 of the present invention will be described. FIG. 3 illustrates a configuration diagram of the hydrogen supply system 100 in which components of the hydrogen concentration adjustment unit 104 in FIG. 2 are illustrated in detail.

[0032] As illustrated in FIG. 3, the hydrogen concentration adjustment unit 104 includes a grid gas hydrogen concentration reception unit 1041, a produced hydrogen flow rate measurement unit 1042, a grid gas flow rate calculation unit 1043, a grid gas flow rate command unit 1044, a gas mixing unit 1045, and a mixed gas supply unit 1046. The hydrogen concentration adjustment unit 104 is connected to the hydrogen boosting unit 102 and the grid gas lead-in unit 103 in the hydrogen supply system 100.

[0033] The grid gas hydrogen concentration reception unit 1041 receives the hydrogen concentration in the grid gas from the grid gas lead-in unit 103. The produced hydrogen flow rate measurement unit 1042 measures a flow rate of the hydrogen produced by the hydrogen production unit 101. The grid gas flow rate calculation unit 1043 calculates a grid gas flow rate at which a hydrogen concentration of the mixed gas becomes equal to or lower than an allowable hydrogen concentration specified in the gas grid 901 from the flow rate of the hydrogen produced by the hydrogen production unit 101. The grid gas flow rate command unit 1044 commands the grid gas flow rate calculated by the grid gas flow rate calculation unit 1043 to the grid gas lead-in unit 103. The gas mixing unit 1045 mixes a specified amount of grid gas supplied from the grid gas lead-in unit 103 and the hydrogen produced by the hydrogen production unit 101. The mixed gas supply unit 1046 supplies the mixed gas mixed by the gas mixing unit 1045 to the mixed gas return unit 105.

[0034] The hydrogen concentration adjustment unit 104 calculates a grid gas flow rate for making the hydrogen concentration in the mixed gas 3 to be supplied to the gas grid 901 equal to or less than the specified value using the grid gas hydrogen concentration data 201 which is the hydrogen concentration in the grid gas and the produced hydrogen flow rate data 203. The grid gas hydrogen concentration data 201 measured by the grid gas hydrogen concentration measurement unit 1031 described in the second embodiment is received by the grid gas hydrogen concentration reception unit 1041 through the grid gas hydrogen concentration communication unit 1032. The produced hydrogen flow rate data 203 is data measured by the produced hydrogen flow rate measurement unit 1042. These two kinds of data are sent to the grid gas flow rate calculation unit 1043. Here, the flow rate of the grid gas 1 to be led by the grid gas lead-in unit 103 needs to flexibly cope with successive fluctuation of the flow rate of the hydrogen to be produced by the hydrogen production unit 101. When a transmission interval of the grid gas hydrogen concentration data 201 is slow and determination of the grid gas flow rate is delayed, the hydrogen concentration in the mixed gas 3 to be supplied to the gas grid 901 exceeds the specified value and cannot be supplied particularly when the produced hydrogen flow rate increases. Thus, a reception interval of the grid gas hydrogen concentration data 201 of the grid gas hydrogen concentration reception unit 1041 and a measurement interval of the produced hydrogen flow rate data 203 of the produced hydrogen flow rate measurement unit 1042 to be used for determining the grid gas flow rate are preferably set to equal to or less than 5 minutes.

[0035] The grid gas flow rate calculation unit 1043 calculates the grid gas flow rate by the following equation (1). F G in equation (1) is the grid gas flow rate [Nm 3< / h], F H2.SUP is the produced hydrogen flow rate [Nm 3< / h], x H2.SET is a target hydrogen concentration [vol%] in the mixed gas, and x H2.G is the grid gas hydrogen concentration [vol%]. Here, the target hydrogen concentration x H2.SET in the mixed gas is set to be equal to or less than the specified value of the hydrogen concentration provided in the gas grid. The method of calculating the grid gas flow rate is not limited to equation (1). F G = 100 − x H 2 . SET / x H 2 . SET − x H 2 . G × F H 2 . SUP

[0036] Here, a calculation example using equation (1) will be described. First, it is assumed that a hydrogen concentration specified value of 20 vol% is provided in the gas grid 901, the produced hydrogen flow rate is 100 Nm 3< / h, the grid gas hydrogen concentration is 10 vol%, and the target hydrogen concentration in the mixed gas is 20 vol%. A hydrogen user preferably increases the hydrogen concentration in the gas grid 901 as much as possible, and thus, the target hydrogen concentration in the mixed gas is set at the specified value of the hydrogen concentration provided in the gas grid 901 in the present embodiment, but is not limited thereto. If the above value is substituted into equation (1), the flow rate of the grid gas to be led by the grid gas lead-in unit 103 is calculated to be 800 Nm 3< / h.

[0037] As described above, the grid gas flow rate command data 202 calculated by the grid gas flow rate calculation unit 1043 is transmitted from the grid gas flow rate command unit 1044 to the grid gas flow rate reception unit 1033, and the grid gas flow rate to be led is adjusted by the grid gas flow rate adjustment unit 1034. Here, an interval of data to be transmitted to the grid gas flow rate reception unit 1033 is preferably set to equal to or less than 5 minutes, similarly to the data reception interval at the grid gas hydrogen concentration reception unit 1041 and the flow rate measurement interval at the produced hydrogen flow rate measurement unit 1042. The specified amount of the grid gas 1 thus adjusted and the hydrogen 2 produced by the hydrogen production unit 101 are mixed at the gas mixing unit 1045. When the mixed gas is supplied to the gas grid 901, it is preferable that there is no distribution of hydrogen in the mixed gas. Thus, the gas mixing unit 1045 preferably mixes the hydrogen 2 and the grid gas by a method such as a pressure ratio mixing method, a weight method, a flow rate mixing method, or a half weight method, but the mixing method is not limited. Thereafter, the mixed gas 3 is supplied from the mixed gas return unit 105 to the gas grid 901 through the mixed gas supply unit 1046.

[0038] According to the hydrogen supply system 100 including the hydrogen concentration adjustment unit 104 of the third embodiment, the hydrogen concentration in the mixed gas adjusted by the hydrogen concentration adjustment unit 104 can be set to be equal to or lower than the specified value of the gas grid 901 even in a case where the produced hydrogen flow rate fluctuates.<<Fourth embodiment>>

[0039] In a fourth embodiment, an example of a method of operating the mixed gas return unit 105 which is one of the components of the hydrogen supply system 100 of the present invention will be described. FIG. 4 is a configuration diagram of the hydrogen supply system 100 in which components of the mixed gas return unit 105 in FIG. 3 are illustrated in detail.

[0040] As illustrated in FIG. 3, the mixed gas return unit 105 includes a mixed gas flow rate measurement unit 1051, a grid gas flow rate balance management unit 1052, a mixed gas gas grid supply unit 1053, and a return gas calorimetry unit 1054. The mixed gas return unit 105 is connected to the hydrogen concentration adjustment unit 104 in the hydrogen supply system 100 and the gas grid 901.

[0041] The mixed gas flow rate measurement unit 1051 measures the flow rate of the mixed gas. The grid gas flow rate balance management unit 1052 manages balance of the grid gas by comparing the grid gas flow rate in the mixed gas obtained by subtracting the produced hydrogen flow rate measured by the produced hydrogen flow rate measurement unit 1042 from the mixed gas flow rate measured by the mixed gas flow rate measurement unit 1051 with the grid gas flow rate commanded by the grid gas flow rate command unit 1044 to the grid gas flow rate adjustment unit 1034. The mixed gas gas grid supply unit 1053 supplies the mixed gas to the gas grid 901.

[0042] As described in the first to the third embodiments, the hydrogen concentration of hydrogen 2 produced by the hydrogen production unit 101 is adjusted by the grid gas lead-in unit 103 and the hydrogen concentration adjustment unit 104. Here, in order to lead the grid gas 1 from the gas grid 901 and supply it to the gas grid 901 again, a hydrogen supplier and a gas grid operator need to manage material balance of the grid gas 1. By managing the balance of the grid gas flow rate, when the hydrogen supplier leads the grid gas, the gas grid operator can set a fee structure different from a fee structure for the existing grid gas user.

[0043] As illustrated in the fourth embodiment, the flow rate of the mixed gas 3 supplied from the hydrogen concentration adjustment unit 104 is measured by the mixed gas flow rate measurement unit 1051 and is transmitted to the grid gas flow rate balance management unit 1052 as mixed gas flow rate data 204. The grid gas flow rate balance management unit 1052 calculates the material balance of the grid gas using the mixed gas flow rate data 204, the produced hydrogen flow rate data 203 measured by the produced hydrogen flow rate measurement unit 1042, and the grid gas flow rate command data 202 determined by the grid gas flow rate calculation unit 1043 and performs management so that the same amount of the grid gas 1 lead from the gas grid 901 is normally returned to the gas grid 901. Here, it is assumed that there is a time difference in each measurement data depending on an operation period of each step and a length of a gas pipe, and the balance of the material is not accurately matched in the data at the same time. It is therefore preferable to manage the balance of the flow rate in a certain time width. A status of the grid gas material balance management is also transmitted to the gas grid operator 106 and is constantly grasped by both.

[0044] Finally, the mixed gas gas grid supply unit 1053 supplies gas to the gas grid 901 using, for example, a blower, or the like. A connection port with the gas grid 901 desirably has a structure in which the return gas is diffused in the gas grid 901 as much as possible.

[0045] According to the hydrogen supply system 100 including the mixed gas return unit 105 of the present embodiment, it is possible to set a fee structure different from a fee structure for the existing grid gas user by managing the material balance of the lead-in grid gas and the grid gas returned to the gas grid 901.

[0046] In addition, a hydrogen supply device supplies the mixed gas 3 to the gas grid 901 by the methods described in the first to third embodiments and the present embodiment, but it is necessary to obtain revenue by charging according to the amount of hydrogen supplied in the mixed gas 3. As a method of this charging, for example, there is a method of calculating a charge amount on a calorie basis.

[0047] Specifically, the return gas calorimetry unit 1054 is provided in the mixed gas return unit 105 in FIG. 4. The return gas calorimetry unit 1054 is a unit that calculates an amount of heat of hydrogen in the supplied mixed gas from an amount of heat [MJ / m 3< ] corresponding to hydrogen content of the mixed gas 3, a flow rate [m 3< / h], and a supply period [h]. A charge amount can be determined on the basis of the amount of heat calculated by the return gas calorimetry unit 1054 and paid to the supplier.

[0048] Then, a used gas calorimetry unit is provided on a hydrogen utilization device side (not illustrated). The used gas calorimetry unit is a unit that calculates an amount of heat of the used gas on the basis of a calorific value [MJ / m 3< ] of the used gas, a flow rate [m 3< / h], and a supply period [h]. By measuring the amount of heat of the used gas by the used gas calorimetry unit, a usage fee can be determined and charged to the user.(Modifications)

[0049] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to those having all the described components. In addition, part of the components of a certain embodiment can be replaced with the components of another embodiment, and the components of another embodiment can be added to the configuration of a certain embodiment. In addition, it is also possible to add, delete, or replace other components for part of the components of each embodiment.

[0050] Some or all of the above-described configurations, functions, processing units, processing means, and the like, may be implemented by hardware such as an integrated circuit, for example. Each of the above-described configurations, functions, and the like, may be implemented by software by a processor interpreting and executing a program for implementing each function. Information such as a program, a table, and a file for implementing each function can be stored in a recording device such as a memory, a hard disk, and a solid state drive (SSD), or a recording medium such as a flash memory card and a digital versatile disk (DVD).

[0051] In addition, in each embodiment, control lines and information lines considered to be necessary for description are illustrated, and not all control lines and information lines in a product are necessarily illustrated. In practice, it may be considered that almost all the components are connected to each other.Reference Signs List

[0052] 1grid gas 2hydrogen 3mixed gas (blend gas) 100hydrogen supply system 101hydrogen production unit 102hydrogen boosting unit 103grid gas lead-in unit 1031grid gas hydrogen concentration measurement unit 1032grid gas hydrogen concentration communication unit 1033grid gas flow rate reception unit 1034grid gas flow rate adjustment unit 1035grid gas supply unit 104hydrogen concentration adjustment unit 1041grid gas hydrogen concentration reception unit 1042produced hydrogen flow rate measurement unit 1043grid gas flow rate calculation unit 1044grid gas flow rate command unit 1045gas mixing unit 1046mixed gas supply unit 105mixed gas return unit 1051mixed gas flow rate measurement unit 1052grid gas flow rate balance management unit 1053mixed gas gas grid supply unit 106gas grid operator 201grid gas hydrogen concentration data 202grid gas flow rate command data 203produced hydrogen flow rate data 204mixed gas flow rate data 901gas grid

Claims

1. A hydrogen supply system (100) comprising: a hydrogen production unit (101) configured to produce hydrogen; a hydrogen boosting unit (102) configured to boost a pressure of the hydrogen produced by the hydrogen production unit (101) to a pressure at which the hydrogen can be supplied to a gas grid (901); a grid gas lead-in unit (103) configured to lead grid gas from the gas grid (901); a hydrogen concentration adjustment unit (104) configured to adjust mixed gas to have a hydrogen concentration equal to or lower than an allowable hydrogen concentration specified in the gas grid (901); and a mixed gas return unit (105) configured to supply the mixed gas to the gas grid, characterised in that the hydrogen concentration adjustment unit (104) is configured to adjust the hydrogen concentration of the mixed gas by changing a grid gas flow rate.

2. The hydrogen supply system (100) according to claim 1, wherein at least blend gas of natural gas and hydrogen flows through the gas grid (901).

3. The hydrogen supply system (100) according to claim 1 or 2, wherein the hydrogen production unit (101) is configured to produce hydrogen by any one of a method of electrolysis of water using electric power generated by renewable energy, a method of reforming natural gas, and a method of producing hydrogen by gasifying coal and causing shift reaction.

4. The hydrogen supply system (100) according to claim 1 or 2, wherein the grid gas lead-in unit (103) includes: a grid gas hydrogen concentration measurement unit (1031) configured to measure a hydrogen concentration in grid gas; a grid gas hydrogen concentration communication unit (1032) configured to transmit data of the hydrogen concentration in the grid gas to the hydrogen concentration adjustment unit (104); a grid gas flow rate reception unit (1033) configured to receive a grid gas flow rate calculated by the hydrogen concentration adjustment unit (104); a grid gas flow rate adjustment unit (1034) configured to adjust and leads the grid gas; and a grid gas supply unit (1035) configured to supply the grid gas to the hydrogen concentration adjustment unit (104).

5. The hydrogen supply system (100) according to any one of claims 1 to 4, wherein the hydrogen concentration adjustment unit (104) includes: a grid gas hydrogen concentration reception unit (1041) configured to receive the hydrogen concentration in the grid gas from the grid gas lead-in unit (103); a produced hydrogen flow rate measurement unit (1042) configured to measure a flow rate of the hydrogen produced by the hydrogen production unit (101); a grid gas flow rate calculation unit (1043) configured to calculate a grid gas flow rate such that the mixed gas has a hydrogen concentration equal to or lower than the allowable hydrogen concentration specified in the gas grid (901) from the flow rate of the hydrogen produced by the hydrogen production unit (101); a grid gas flow rate command unit (1044) configured to command the grid gas flow rate calculated by the grid gas flow rate calculation unit (1043); a gas mixing unit (1045) configured to mix a designated amount of the grid gas supplied from the grid gas lead-in unit (103) and the hydrogen produced by the hydrogen production unit (101); and a mixed gas supply unit (1046) configured to supply the mixed gas mixed by the gas mixing unit (1045) to the mixed gas return unit (105).

6. The hydrogen supply system (100) according to claim 5, wherein the mixed gas return unit (105) includes: a mixed gas flow rate measurement unit (1051) configured to measure a flow rate of the mixed gas; and a grid gas flow rate balance management unit (1052) configured to manage balance of the grid gas by comparing a grid gas flow rate in the mixed gas obtained by subtracting the produced hydrogen flow rate measured by the produced hydrogen flow rate measurement unit (1042) from the mixed gas flow rate measured by the mixed gas flow rate measurement unit (1051) with the grid gas flow rate commanded by the grid gas flow rate command unit (1044).

7. The hydrogen supply system (100) according to claim 6, wherein the mixed gas return unit (105) further includes a return gas calorimetry unit (1054) configured to measure an amount of heat of hydrogen in the return gas.

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