Hydrogen production system and hydrogen production method

Abstract

[Problem] To produce hydrogen while avoiding the discharge of carbon dioxide by a simple constitution without depending on fossil fuels. [Solution] A hydrogen production system 1 comprises: a biogas generation device 2 that generates a biogas which contains first methane and carbon dioxide from biomass; a hydrogenation device 3 that generates second methane by hydrogenation of the carbon dioxide contained in the biogas, thereby generating a hydrogenated gas containing the first and second methane; a thermal decomposition device 5 that generates hydrogen and solid carbon by direct decomposition of the first and second methane; and a generated hydrogen supply line L3 that is connected to the hydrogenation device 3 and is for supplying some of the hydrogen generated by the thermal decomposition device 5 to the hydrogenation device 3. In a normal operation state, the hydrogenation device 3 generates the second methane using only the hydrogen supplied from the generated hydrogen supply line L3.

Description

Hydrogen production system and hydrogen production method

[0001] The present invention relates to a hydrogen production system and a hydrogen production method for producing hydrogen derived from biomass.

[0002] In recent years, in order to achieve a carbon-neutral society, hydrogen has attracted attention as a clean energy source that does not emit carbon dioxide during use. In particular, so-called turquoise hydrogen (i.e., hydrogen produced by direct decomposition of methane) has the advantages that its production cost is relatively low, and carbon as a by-product is recovered as a solid during production, so no carbon dioxide is emitted.

[0003] Also, regarding the technology for generating methane, there is known a system including a biogas generator that generates biogas containing carbon dioxide, a water decomposition device that decomposes water into hydrogen and oxygen, and a methanation device that generates methane gas by reacting carbon dioxide contained in the biogas with hydrogen supplied from the water decomposition device (see Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2019-90084

[0005] By the way, when producing turquoise hydrogen, by using methane derived from renewable and sustainable biomass, there is no need to rely on fossil fuels such as natural gas for hydrogen production. However, biogas generated from biomass based on the methane fermentation method contains carbon dioxide as a by-product.

[0006] Therefore, it is conceivable to produce methane by methanation that reacts carbon dioxide and hydrogen in biogas as in the prior art described in Patent Document 1 above. However, in the above prior art, since it is necessary to provide a water decomposition device for generating hydrogen used for methanation, there is a problem that the system configuration becomes complicated.

[0007] In view of the above background, an object of the present invention is to provide a hydrogen production system and a hydrogen production method that can produce hydrogen while avoiding carbon dioxide emissions with a simple configuration without relying on fossil fuels (e.g., natural gas).

[0008] To solve the above problems, one aspect of the present invention provides a hydrogen production system for producing biomass-derived hydrogen, comprising: a biogas generator that generates biogas containing a first methane and carbon dioxide from biomass; a hydrogenation device that generates a hydrogenated gas containing the first and second methanes by generating a second methane by hydrogenating the carbon dioxide contained in the biogas; a pyrolysis device that generates hydrogen and solid carbon by the direct decomposition of the first and second methanes; and a hydrogen production supply line connected to the hydrogenation device for supplying a portion of the hydrogen produced by the pyrolysis device to the hydrogenation device, wherein the hydrogenation device is configured to generate the second methane using only the hydrogen supplied from the hydrogen production supply line in its normal operating state.

[0009] According to this embodiment, since a portion of the hydrogen produced in the pyrolysis apparatus is supplied to the hydrogenation apparatus, there is no need for a dedicated apparatus (e.g., a water splitting apparatus) to produce the hydrogen used for hydrogenation of carbon dioxide. Therefore, hydrogen can be produced with a simple configuration without relying on fossil fuels, while avoiding carbon dioxide emissions.

[0010] In the above embodiment, the hydrogen further comprises a hydrogen tank for storing hydrogen and a hydrogen storage supply line for supplying the hydrogen stored in the hydrogen tank to the hydrogenation apparatus, wherein the hydrogenation apparatus may generate the second methane using the hydrogen supplied from the hydrogen storage supply line in the startup state prior to the normal operating state.

[0011] According to this embodiment, when the hydrogen production system starts up, hydrogen stored in the hydrogen tank is supplied to the hydrogenation unit through the hydrogen storage supply line, thereby making it easy to start hydrogen production by the hydrogenation unit.

[0012] In the above embodiment, the hydrogen storage supply line may constitute at least a part of the hydrogen production supply line.

[0013] According to this embodiment, since the stored hydrogen supply line constitutes at least a part of the generated hydrogen supply line, hydrogen used for the hydrogenation of carbon dioxide can be supplied to the hydrogenation device with a simple configuration.

[0014] In the above embodiment, it is preferable that the hydrogen tank be capable of storing the hydrogen produced by the pyrolysis apparatus.

[0015] According to this embodiment, the hydrogen produced in the pyrolysis apparatus is stored in a hydrogen tank, thereby enabling a stable supply of an appropriate amount of hydrogen to the hydrogenation apparatus.

[0016] In the above embodiment, the hydrogenation apparatus may produce the second methane by a methanation reaction of carbon dioxide and hydrogen in the presence of a catalyst.

[0017] According to this embodiment, the production of a second methane by hydrogenation of carbon dioxide can be stably carried out using a methanation reaction.

[0018] In the above embodiment, the hydrogenation apparatus may produce the second methane by a methane production reaction of carbon dioxide and hydrogen in the presence of microorganisms.

[0019] According to this embodiment, the production of a second methane by hydrogenation of carbon dioxide can be stably carried out using microorganisms.

[0020] In the above embodiment, the biogas generating apparatus may include a fermentation apparatus with an electroculture device that holds microorganisms that generate biogas from organic matter contained in the biomass and has electrodes for exchanging electrons with the microorganisms.

[0021] According to this embodiment, the composition of the biogas (i.e., the ratio of first methane and carbon dioxide) can be changed by controlling the growth or metabolism of microorganisms in the fermentation apparatus (i.e., electroculture), thereby allowing the amount of hydrogen required by the hydrogenation apparatus to be appropriately adjusted.

[0022] To solve the above problems, one aspect of the present invention is a hydrogen production method for producing hydrogen derived from biomass, comprising: generating a biogas containing a first methane and carbon dioxide from biomass; generating a second methane by hydrogenating the carbon dioxide contained in the biogas; generating hydrogen and solid carbon by the direct decomposition of the first and second methanes; and in the hydrogenation of carbon dioxide, the second methane is produced using only a portion of the hydrogen generated by the direct decomposition of the first and second methanes.

[0023] According to this embodiment, since a portion of the hydrogen produced by thermal decomposition is used for hydrogenating carbon dioxide, there is no need for a dedicated device (e.g., a water splitting device) to produce the hydrogen used for hydrogenating carbon dioxide. Therefore, hydrogen can be produced with a simple configuration without relying on fossil fuels, while avoiding carbon dioxide emissions.

[0024] According to the above embodiment, it becomes possible to produce hydrogen without relying on fossil fuels and while avoiding carbon dioxide emissions.

[0025] Schematic diagram showing the overall configuration of the hydrogen production system according to the first embodiment. Schematic diagram showing the overall configuration of the hydrogen production system according to the second embodiment. Schematic diagram showing a modified example of the hydrogen production system shown in Figure 2.

[0026] The hydrogen production system and hydrogen production method according to the embodiment will be described below with reference to the drawings.

[0027] (First Embodiment) The hydrogen production system 1 is a system for producing hydrogen derived from biomass. As shown in Figure 1, the hydrogen production system 1 includes a fermentation device 2 (an example of a biogas generator), a hydrogenation device 3, a first hydrogen tank 4, a pyrolysis device 5, a second hydrogen tank 6, a carbon containment device 7, an energy supply device 8, and a control device 9.

[0028] The fermentation apparatus 2 produces biogas containing methane (hereinafter referred to as "first methane" as needed) and carbon dioxide from biomass. The fermentation apparatus 2 includes known components such as a fermentation tank (not shown) that uses anaerobic microorganisms to perform methane fermentation on the biomass raw material 11. The fermentation tank has an airtight structure so as to be able to maintain an oxygen-free state. Furthermore, the fermentation apparatus 2 may be equipped with a stirring device for stirring the inside of the fermentation tank, a heater for heating the inside of the fermentation tank, a desulfurization device, a sterilization device, and sensors (e.g., a thermometer, a liquid level gauge).

[0029] Biomass can include, for example, food waste, sewage sludge, livestock manure, crop residues, and wood.

[0030] In fermentation apparatus 2, hydrolysis of biomass, production of organic acids by microorganisms, and production of methane gas by microorganisms take place. Finally, in fermentation apparatus 2, biogas derived from the biomass raw material 11 is produced by known methane-producing anaerobic microorganisms under anaerobic conditions in the fermentation tank. The biogas contains methane (CH4) and carbon dioxide (CO2). Here, the biogas contains 60% (v / v) methane and 40% (v / v) carbon dioxide by volume percentage. However, the composition of the biogas may vary depending on the type of biomass raw material 11 and the processing conditions of methane fermentation. In addition, the biogas may contain components other than methane and carbon dioxide (for example, impurities such as nitrogen, oxygen, and hydrogen sulfide).

[0031] The biomass raw material 11 processed in the fermentation apparatus 2 is discharged from the fermentation tank and used as compost 12. The methane-producing bacteria that generate biogas can be appropriately selected from several known types of bacteria.

[0032] The hydrogenation device 3 hydrogenates the carbon dioxide contained in the biogas produced by the fermentation device 2. The hydrogenation device 3 includes known components such as a hydrogenation reactor (not shown) that carries out the methanation reaction of the carbon dioxide contained in the biogas. A catalyst for activating the methanation reaction is placed inside the hydrogenation reactor, and the methanation reaction is carried out in the presence of the catalyst.

[0033] Catalysts used in methanation reactions include, for example, known solid catalysts in which one or more metals selected from nickel, ruthenium, rhodium, potassium, calcium, sodium, and iridium are supported on an oxide support.

[0034] A biogas transport line L1 is provided between the fermentation unit 2 and the hydrogenation unit 3. The biogas transport line L1 includes piping, pumps, valves, measuring instruments, and controllers (not shown in the figures) (the same applies to other "lines" hereafter unless otherwise specified).

[0035] The hydrogenation unit 3 is connected to the first hydrogen tank 4 via the hydrogen storage supply line L2. The first hydrogen tank 4 stores the start-up hydrogen necessary for the methanation reaction in the hydrogenation unit 3 when the hydrogen production system 1 is started up (i.e., in the start-up state).

[0036] Furthermore, a hydrogen production supply line L3 and a methane transport line L4 are provided between the hydrogenation unit 3 and the pyrolysis unit 5.

[0037] Biogas is supplied to the hydrogenation unit 3 from the fermentation unit 2 at a predetermined flow rate through the biogas transport line L1. Hydrogen is also supplied to the hydrogenation unit 3 through the hydrogen storage supply line L2. As a result, the methanation reaction of carbon dioxide contained in the biogas is carried out in the hydrogenation unit 3, for example, at a temperature of about 300°C to 500°C, as shown in the following equation (1). As a result, methane (hereinafter referred to as "second methane" as needed) is produced from carbon dioxide in the hydrogenation unit 3.

[0038] CO ２ + 4H2 → CH4 + 2H2O ... (1)

[0039] Note that the hydrogen supply from the first hydrogen tank 4 to the hydrogenation device 3 is temporarily executed. That is, when the hydrogen production system 1 reaches a steady state (i.e., after shifting from the operation start state to the normal operation state), the hydrogen supply from the first hydrogen tank 4 to the hydrogenation device 3 is stopped, and the supply of hydrogen is started through the generated hydrogen supply line L3 from the thermal decomposition device 5. That is, in the hydrogen production system 1, when it reaches a steady state, the second methane can be generated using only the hydrogen generated in the thermal decomposition device 5 (i.e., the hydrogen in the system).

[0040] Note that the hydrogenation device 3 is not limited to the methanation reaction as described above. For example, the second methane can also be generated by the methane production reaction of carbon dioxide and hydrogen in the presence of microorganisms such as methane-producing bacteria.

[0041] The thermal decomposition device 5 generates hydrogen and solid carbon by directly decomposing methane (i.e., the first and second methane). The thermal decomposition device 5 includes a known configuration such as a methane decomposition reactor (not shown) that performs the direct decomposition reaction of methane. Inside the methane decomposition reactor, a catalyst for activating the direct decomposition reaction of methane is arranged.

[0042] The catalysts used for the direct decomposition reaction of methane include, for example, an iron catalyst supported on alumina, a catalyst with a nickel layer laminated on a copper plate, and the like.

[0043] The second hydrogen tank 6 is connected to the thermal decomposition device 5 via the hydrogen transport line L5. The second hydrogen tank 6 stores the hydrogen generated by the direct decomposition reaction of methane (excluding the hydrogen supplied to the hydrogenation device 3). Further, a carbon storage device 7 for accommodating the solid carbon generated by the direct decomposition reaction of methane is attached to the thermal decomposition device 5. The carbon storage device 7 is provided so as to be able to receive the carbon discharged from the methane decomposition reactor.

[0044] The thermal decomposition device 5 is connected to an energy supply device 8 via an energy supply line L6. The energy supply device 8 supplies the energy necessary for the direct decomposition reaction of methane to the thermal decomposition device 5. As the energy supplied to the thermal decomposition device 5, renewable energy obtained from sunlight, wind power, geothermal heat, etc. is utilized.

[0045] For example, the energy supply device 8 includes at least one of a solar panel, a wind turbine, a hydroelectric power turbine, and a geothermal power generation device that generates electric energy, and can supply electric power to the thermal decomposition device 5. In this case, the energy supply line L6 includes an electric cable. Also, for example, the energy supply device 8 includes a solar collector and can supply heat to the thermal decomposition device 5 via a heat medium. In this case, the energy supply line L6 includes piping for circulating the heat medium, etc.

[0046] Methane is supplied to the thermal decomposition device 5 from the hydrogenation device 3 at a predetermined flow rate through a methane transport line L4. Thereby, in the thermal decomposition device 5, for example, in a methane decomposition reactor adjusted to a temperature of about 600°C to 900°C, the direct decomposition reaction of methane shown in the following formula (2) is executed. Thereby, in the thermal decomposition device 5, hydrogen and solid carbon are generated from methane.

[0047] CH4 → C + 2H2 ・・・(2)

[0048] Note that the thermal decomposition device 5 can also perform the direct decomposition of methane using high-temperature plasma based on a known plasma decomposition method, for example, by including a plasma generation device.

[0049] A part of the hydrogen generated in the thermal decomposition device 5 is supplied to the hydrogenation device 3 through a generated hydrogen supply line L3. Also, among the hydrogen generated in the thermal decomposition device 5, the hydrogen other than that supplied to the hydrogenation device 3 is sent to a second hydrogen tank 6 through a hydrogen transport line L5. The hydrogen stored in the second hydrogen tank 6 is used for any purpose (fuel, synthesis of organic compounds, food processing, etc.).

[0050] Furthermore, the solid carbon produced in the pyrolysis apparatus 5 is stored in the carbon containment apparatus 7. The carbon stored in the carbon containment apparatus 7 can be used for any purpose (such as raw materials for carbon electrodes, carbon fibers, catalysts, etc.). In addition, the solid carbon produced can be used as carbon black added to asphalt.

[0051] Thus, in hydrogen production system 1, by generating solid carbon, CO ２ Instead of using methods such as CCS (Carbon dioxide Capture and Storage), which stores CO2 under extremely high pressure deep on the seabed, ２ It can be easily and stably stored on land.

[0052] In the hydrogen production system 1, the hydrogen production supply line L3 is equipped with a flow control valve 21 that can adjust the flow rate of hydrogen supplied to the hydrogenation device 3. The biogas transport line L1 is equipped with a flow meter 22 that measures the flow rate of biogas. The control device 9 includes a PLC (Programmable Logic Controller), etc. The control device 9 can control the flow control valve 21 based on the biogas flow rate (i.e., measurement result) obtained from the flow meter 22. This appropriately adjusts the amount of hydrogen supplied to the hydrogenation device 3 through the hydrogen production supply line L3.

[0053] In the hydrogen production system 1, for example, if biogas containing 1.7 kg-mol / h of methane and 1.1 kg-mol / h of carbon dioxide is supplied from the fermentation unit 2 to the hydrogenation unit 3, 4.5 kg-mol / h of hydrogen will be supplied from the pyrolysis unit 5 (or the first hydrogen tank 4) to the hydrogenation unit 3 as hydrogen for the methanation reaction. In addition, the pyrolysis unit 5 will produce 1.2 kg-mol / h of hydrogen (excluding the hydrogen supplied to the hydrogenation unit 3) and 2.8 kg-mol / h of carbon. However, the amounts of methane, hydrogen, carbon dioxide, and carbon may vary depending on the specifications of each device that actually constitutes the hydrogen production system 1.

[0054] In this hydrogen production system 1, hydrogen stored in the first hydrogen tank 4 is supplied to the hydrogenator via the storage hydrogen supply line L2 at the start of operation, thereby easily initiating hydrogen production by the hydrogenator 3. Subsequently, once the hydrogen production system 1 reaches a steady state (i.e., steady operation), a portion of the hydrogen produced in the pyrolysis unit 5 is stably supplied to the hydrogenator 3. As a result, the hydrogen production system 1 does not require a dedicated device (e.g., a water splitting unit) to produce the hydrogen used for hydrogenation of carbon dioxide. Therefore, according to the hydrogen production system 1, hydrogen can be produced with a simple configuration without relying on fossil fuels, while avoiding carbon dioxide emissions.

[0055] (Second Embodiment) Next, with reference to Figure 2, the hydrogen production system 1 according to the second embodiment will be described. In the drawings and description relating to the second embodiment, components similar to those in the first embodiment described above are denoted by the same reference numerals as those used in the first embodiment. Furthermore, the configuration and operation of each element in the hydrogen production system 1 according to the second embodiment are the same as those in the hydrogen production system 1 according to the first embodiment, except for matters specifically mentioned below.

[0056] In the hydrogen production system 1 according to the second embodiment, the arrangement of the first hydrogen tank 4 differs from that of the first embodiment described above. The first hydrogen tank 4 is located in the middle of the hydrogen production supply line L3. As a result, the hydrogen supplied from the pyrolysis apparatus 5 to the hydrogenation apparatus 3 through the hydrogen production supply line L3 is temporarily stored in the first hydrogen tank 4 before being supplied from the first hydrogen tank 4 to the hydrogenation apparatus 3.

[0057] Furthermore, since it is difficult to supply hydrogen from the pyrolysis unit 5 when the hydrogen production system 1 is started up (i.e., in the initial operation state), it is preferable that the first hydrogen tank 4 has hydrogen for starting up (i.e., external hydrogen) stored in advance. Here, the storage hydrogen supply line L2 for transporting the hydrogen for starting up constitutes at least a part of the generated hydrogen supply line L3. This makes it possible to supply hydrogen used for hydrogenating carbon dioxide to the hydrogenation unit 3 with a simple configuration.

[0058] (Modified Versions) Next, with reference to Figure 3, modified versions of the hydrogen production system 1 shown in Figure 2 will be described. In the drawings and descriptions relating to the modified versions of the hydrogen production system 1, components similar to those in the first or second embodiment described above are denoted by the same reference numerals as those used in the first or second embodiment. Furthermore, the configuration and operation of each element in the modified versions of the hydrogen production system 1 are the same as those of the corresponding elements in the hydrogen production system 1 according to the first or second embodiment, except for matters specifically mentioned below.

[0059] A modified version of the hydrogen production system 1 differs from the second embodiment in that a fermentation apparatus with an electroculture device 102 (an example of a biogas production apparatus) is used instead of the fermentation apparatus 2 shown in Figure 2. The fermentation apparatus with an electroculture device 102 is equipped with an anode electrode and a cathode electrode (not shown), and the current flow between the two electrodes is controlled by a device (not shown). Microorganisms such as methanogenic bacteria are introduced into the fermentation apparatus with an electroculture device 102. By controlling the oxidation-reduction state inside the fermentation apparatus with an electroculture device 102 using a potential control device (exchanging electrons with the microorganisms), the growth and metabolism of the microorganisms can be promoted.

[0060] Furthermore, in the hydrogen production system 1, the composition of the biogas (i.e., the ratio of the first methane and carbon dioxide) can be changed by voltage control using a potential control device, so that the amount of hydrogen required by the hydrogenation device 3 can be appropriately adjusted. As a result, the amount of hydrogen stored in the second hydrogen tank 6 per unit time can be controlled.

[0061] Furthermore, the fermentation apparatus 102 with an electroculture device described above can also be used in place of the fermentation apparatus 2 in the hydrogen production system 1 according to the first embodiment shown in Figure 1.

[0062] This concludes the description of embodiments, including specific examples. However, the present invention is not limited to the above embodiments or modifications and can be broadly modified and implemented. Not all components of the hydrogen production system and hydrogen production method shown in the above embodiments (including modifications) are necessarily essential, and at least those skilled in the art can appropriately select and omit them as long as they do not deviate from the scope of the present invention.

[0063] 1: Hydrogen production system 2: Fermentation apparatus 3: Hydrogenation apparatus 4: First hydrogen tank 5: Pyrolysis apparatus 6: Second hydrogen tank 7: Carbon containment apparatus 8: Energy supply apparatus 9: Control device 11: Biomass raw material 12: Compost 21: Flow control valve 22: Flow meter 102: Fermentation apparatus with electroculture apparatus L1: Biogas transport line L2: Stored hydrogen supply line L3: Generated hydrogen supply line L4: Methane transport line L5: Hydrogen transport line L6: Energy supply line

Claims

1. A hydrogen production system for producing hydrogen derived from biomass, comprising: a biogas generator that produces biogas containing a first methane and carbon dioxide from biomass; a hydrogenation device that produces a hydrogenated gas containing the first and second methanes by hydrogenating the carbon dioxide contained in the biogas to produce a second methane; a pyrolysis device that produces hydrogen and solid carbon by the direct decomposition of the first and second methanes; and a hydrogen production supply line connected to the hydrogenation device for supplying a portion of the hydrogen produced by the pyrolysis device to the hydrogenation device, wherein the hydrogenation device, under normal operating conditions, produces the second methane using only the hydrogen supplied from the hydrogen production supply line.

2. The hydrogen production system according to claim 1, further comprising a hydrogen tank for storing hydrogen, and a hydrogen storage supply line for supplying the hydrogen stored in the hydrogen tank to the hydrogenation device, wherein the hydrogenation device, in an operational start state prior to the normal operating state, produces the second methane using the hydrogen supplied from the hydrogen storage supply line.

3. The hydrogen production system according to claim 2, wherein the hydrogen storage supply line constitutes at least a part of the hydrogen production supply line.

4. The hydrogen production system according to claim 3, wherein the hydrogen tank is capable of storing the hydrogen produced by the pyrolysis apparatus.

5. The hydrogen production system according to claim 1, wherein the hydrogenation apparatus produces the second methane by a methanation reaction of carbon dioxide and hydrogen in the presence of a catalyst.

6. The hydrogen production system according to claim 1, wherein the hydrogenation apparatus produces the second methane by a methane production reaction of carbon dioxide and hydrogen in the presence of microorganisms.

7. The hydrogen production system according to claim 1, wherein the biogas generating apparatus comprises a fermentation apparatus with an electroculture device having electrodes for exchanging electrons with the biogas generating apparatus, which holds microorganisms that generate the biogas from organic matter contained in the biomass.

8. A hydrogen production method for producing hydrogen derived from biomass, comprising: generating a biogas containing a first methane and carbon dioxide from biomass; generating a second methane by hydrogenating the carbon dioxide contained in the biogas; generating hydrogen and solid carbon by the direct decomposition of the first and second methanes; and in the hydrogenation of carbon dioxide, the second methane is produced using only a portion of the hydrogen generated by the direct decomposition of the first and second methanes.

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