Control device, electrolytic system, control method, and control program

Abstract

Provided are a control device, an electrolytic system, a control method, and a control program that make it possible to suppress a peak voltage. A control device (50) controls a power supply circuit (30) for electrolytic devices (203). The control device (50) determines whether or not a predetermined condition is satisfied. When it is determined that the condition is not satisfied, control is performed to switch the power supply circuit (30) so that the electrolytic devices (203) are connected in parallel. When it is determined that the condition is satisfied, control is performed to switch the power supply circuit (30) so that the electrolytic devices (203) are connected in series.

Description

Control device, electrolysis system, control method, and control program

[0001] The present disclosure relates to a control device, an electrolysis system, a control method, and a control program.

[0002] Water electrolysis, which electrochemically decomposes water to produce hydrogen and oxygen, is a hydrogen production method that does not involve carbon dioxide emissions. Water electrolysis has excellent environmental properties. There are various types of water electrolysis, including alkaline electrolysis and solid polymer electrolysis, which electrolyze liquid water, and steam electrolysis, which electrolyzes water vapor.

[0003] Solid oxide electrolysis cells (SOECs) (hereinafter referred to as "electrolysis cells") that electrolyze high-temperature steam use ceramics with oxygen ion conductivity, such as yttria-stabilized zirconia, as the electrolyte, and can utilize the thermal energy of high-temperature steam as part of the energy required for the electrolysis reaction. Electrolysis cells can produce hydrogen more efficiently than other electrolysis methods. Co-electrolysis is also possible, in which a mixed gas of high-temperature steam and carbon dioxide (CO2) is supplied, and the hydrogen and carbon dioxide produced by electrolysis are reacted in the electrolysis cell to directly produce carbon monoxide (CO) and hydrocarbon compounds.

[0004] Some solid oxide electrolysis cells are being developed as reversible solid oxide electrochemical cells (RSOCs; hereinafter referred to as "reversible cells") that have the two-way function of producing hydrogen and oxygen through a reverse reaction when supplied with external electric power and high-temperature steam, and of generating electricity as a fuel cell.

[0005] In this specification, a cell that functions as both a fuel cell that generates electricity and an electrolysis cell that performs water electrolysis is called an electrochemical cell, and a stack that functions as both a fuel cell stack and an electrolysis cell stack is called an electrochemical cell stack.

[0006] In an SOEC system, the electrolysis cell stack is connected in series or in parallel to a rectifier. In Patent Document 1, the electrolysis cell stack is connected in parallel to a rectifier.

[0007] JP 2023-157554 A

[0008] In the invention of Patent Document 1, the electrolysis cell stack is connected in parallel to the rectifier, which increases the required current. However, the rectifier must be operated at an output current not exceeding its allowable output current, which limits the number of parallel connections. If the electrolysis cell stack is connected in series to the rectifier, for example, when the electrolysis cell stack is energized for electrolysis, the peak voltage may exceed the allowable output voltage of the rectifier during temperature rise due to internal heat generation. To prevent this, it is necessary to reduce the voltage supplied to the electrolysis cell stack.

[0009] The present disclosure has been made in consideration of the above circumstances, and aims to provide a control device, an electrolysis system, a control method, and a control program that are capable of suppressing peak voltage.

[0010] In order to solve the above problems, the control device, electrolysis system, control method, and control program of the present disclosure employ the following means: The control device of the present disclosure controls a power supply circuit of an electrolysis device, determines whether a predetermined condition is satisfied, and, if it determines that the condition is not satisfied, performs control to switch the power supply circuit so that the electrolysis device is connected in parallel.

[0011] The electrolysis system of the present disclosure includes a module having a plurality of electrolyzers, a rectifier, and the aforementioned controller.

[0012] The control method disclosed herein is a control method for controlling a power supply circuit of an electrolysis device, in which a computer determines whether or not a predetermined condition is met, and if it determines that the condition is not met, switches the power supply circuit so that the electrolysis device is connected in parallel.

[0013] The control program of the present disclosure causes a computer to execute the above-described control method.

[0014] According to the present disclosure, the peak voltage of the cell voltage of the electrolysis device can be suppressed.

[0015] FIG. 1 is a diagram illustrating an aspect of an electrolysis cell stack according to some embodiments of the present disclosure; FIG. 2 is a diagram illustrating an aspect of an electrolysis cell cartridge according to some embodiments of the present disclosure; FIG. 3 is a diagram illustrating an aspect of a cross section of an electrolysis cell module according to some embodiments of the present disclosure; FIG. 4 is a diagram illustrating an aspect of an electrolysis system according to some embodiments of the present disclosure; FIG. 5 is a diagram illustrating an example of a hardware configuration of a control device according to some embodiments of the present disclosure; FIG. 6 is a circuit diagram illustrating a parallel connection according to some embodiments of the present disclosure; FIG. 7 is a circuit diagram illustrating a series connection according to some embodiments of the present disclosure; FIG. 8 is a diagram illustrating the relationship between current, cell voltage, and cell temperature according to some embodiments of the present disclosure; and FIG. 9 is a diagram illustrating a time chart for switching a power supply circuit according to some embodiments of the present disclosure.

[0016] Although a cylindrical solid oxide electrolysis cell will be described as an example of a cell stack of a solid oxide electrolysis cell (SOEC), this is not necessarily limited thereto, and a flat cell stack, for example, may also be used. The electrolysis cell is formed on a substrate, but an electrode (hydrogen electrode or oxygen electrode) may be formed thickly and serve as the substrate instead of the substrate. Hereinafter, one embodiment of the structure and materials of a cylindrical solid oxide electrolysis cell according to the present disclosure will be described with reference to the drawings.

[0017] For ease of explanation, the positional relationships of the components described using the expressions "upper" and "lower" with respect to the plane of the paper indicate the vertically upper and lower sides, respectively. In this embodiment, for components that can obtain similar effects in the vertical and horizontal directions, the vertical direction on the plane of the paper is not necessarily limited to the vertically upper and lower directions, but may correspond to, for example, a horizontal direction perpendicular to the vertical direction.

[0018] First, referring to FIG. 1 , a cylindrical cell stack using a substrate tube will be described as an example according to this embodiment. When a substrate tube is not used, for example, a thick anode electrode may be formed to double as the substrate tube; the use of a substrate tube is not limited. In this embodiment, the substrate tube is described as being cylindrical; however, the substrate tube may have any shape as long as it is cylindrical, and the cross section is not necessarily limited to a circular shape; for example, it may be elliptical. A cell stack such as a flat tubular cylinder, in which the peripheral side of a cylinder is crushed vertically, may also be used. Here, FIG. 1 shows one aspect of a cell stack according to this embodiment. The cell stack 101 includes, for example, a cylindrical substrate tube 103, multiple electrolysis cells 105 formed on the outer circumferential surface of the substrate tube 103, and interconnectors 107 formed between adjacent electrolysis cells 105. The electrolysis cells 105 are formed by stacking a hydrogen electrode 109, a solid electrolyte membrane 111, and an oxygen electrode 113. The cell stack 101 includes a lead film 117 electrically connected via an interconnector 107 to the oxygen electrode 113 of the electrolytic cell 105 formed at one end in the axial direction of the base tube 103 out of a plurality of electrolytic cells 105 formed on the outer peripheral surface of the base tube 103, and a lead film 117 electrically connected to the hydrogen electrode 109 of the electrolytic cell 105 formed at the other end. The gas supplied to and discharged from the hydrogen electrode 109 often contains hydrogen in addition to the water vapor used for electrolysis, but in the following description, to avoid confusion, the supply gas containing hydrogen will be referred to as "supplied water vapor" and the hydrogen gas containing water vapor discharged from the hydrogen electrode will be referred to as "produced hydrogen."

[0019] The base tube 103 is made of a porous material, and its main component is, for example, CaO-stabilized ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ+NiO), Y2O3-stabilized ZrO2 (YSZ), or MgAl2O4. The base tube 103 supports the electrolytic cell 105, the interconnector 107, and the lead film 117, and also diffuses the supply steam supplied to the inner circumferential surface of the base tube 103 through the pores of the base tube 103 to the hydrogen electrode 109 formed on the outer circumferential surface of the base tube 103.

[0020] The hydrogen electrode 109 is made of a composite oxide of Ni and a zirconia-based electrolyte material, such as Ni / YSZ. The thickness of the hydrogen electrode 109 is 50 μm to 250 μm, and the hydrogen electrode 109 may be formed by screen-printing a slurry. The solid electrolyte film 111 is typically made of YSZ, which has gas-tight properties and high oxygen ion conductivity at high temperatures. This solid electrolyte film 111 transfers oxygen ions (O 2 − ) generated at the hydrogen electrode to the oxygen electrode. The thickness of the solid electrolyte film 111 located on the surface of the hydrogen electrode 109 is 5 μm to 100 μm, and the solid electrolyte film 111 may be formed by screen-printing a slurry. The oxygen electrode 113 is made of, for example, LaSrMnO 3 -based oxide or LaCoO 3 -based oxide, and the oxygen electrode 113 is formed by screen-printing or applying a slurry using a dispenser. The oxygen electrode 113 may also have a two-layer structure. In this case, the oxygen electrode layer (oxygen electrode intermediate layer) on the solid electrolyte membrane 111 side is made of a material that exhibits high ionic conductivity and excellent catalytic activity. The oxygen electrode intermediate layer may be made of Sm-doped ceria, which exhibits high ionic conductivity, and the oxygen electrode layer (oxygen electrode conductive layer) on the oxygen electrode intermediate layer may be made of a perovskite-type oxide such as Sr- and Ca-doped LaMnO.

[0021] By applying a negative voltage to the hydrogen electrode 109 and a positive voltage to the oxygen electrode 113, the water vapor contained in the supplied water vapor receives electrons at the hydrogen electrode 109 and is electrolyzed to generate hydrogen molecules and oxygen ions (O2-) (see reaction formula (1) below). The generated hydrogen is extracted to the outside together with the supplied water vapor. Meanwhile, the oxygen ions pass through the solid electrolyte membrane 111 due to the potential difference, move to the oxygen electrode 113, release electrons, and become oxygen molecules (see reaction formula (2) below). The generated oxygen is exhausted to the outside together with the oxidizing gas supplied to the oxygen electrode. H2O + 2e- → H2 + O2- ... (1) 2O2- → O2 + 4e- ... (2)

[0022] The oxidizing gas is not directly involved in the electrolysis reaction, but it supplies the heat necessary for the electrolysis reaction (endothermic) and discharges excess heat generated by the electrolysis reaction. It is usually a gas containing approximately 15% to 30% oxygen, and air is a typical example, but other gases that can be used include a mixture of combustion exhaust gas and air, a mixture of oxygen and air, and inert gases such as nitrogen.

[0023] The interconnector 107 is made of a conductive perovskite oxide represented by M1-xLxTiO3 (M is an alkaline earth metal element, L is a lanthanoid element) such as SrTiO3 or lanthanum chromite (LaCrO3), and is screen-printed as a slurry. The interconnector 107 is a dense film that prevents mixing of the supplied water vapor and the oxidizing gas. The interconnector 107 has stable durability and electronic conductivity in both oxidizing and reducing atmospheres. This interconnector 107 electrically connects the oxygen electrode 113 of one electrolytic cell 105 to the hydrogen electrode 109 of the other electrolytic cell 105 in adjacent electrolytic cells 105, thereby connecting the adjacent electrolytic cells 105 in series.

[0024] The lead film 117 is required to have electronic conductivity and a thermal expansion coefficient close to that of the other materials constituting the cell stack 101, and is therefore made of a composite material of Ni and a zirconia-based electrolyte material, such as Ni / YSZ, or an M1-xLxTiO3 (M is an alkaline earth metal element, L is a lanthanoid element) such as an SrTiO3-based material. This lead film 117 applies DC power required for the electrolytic reaction to the multiple electrolytic cells 105 connected in series by the interconnectors 107 to the end of the cell stack 101. The surface on the oxidizing gas side may be protected with an airtight oxidation-resistant material to prevent oxidation of metal materials such as Ni.

[0025] Next, the SOEC cartridge and module according to this embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 shows one embodiment of the solid oxide electrolysis cell (SOEC) cartridge according to this embodiment. Fig. 3 shows a cross-sectional view of one embodiment of the solid oxide electrolysis cell (SOEC) module according to this embodiment.

[0026] As shown in Figure 2, the cartridge 203 includes a plurality of cell stacks 101, steam electrolysis chambers 215, a steam supply header 217, a product hydrogen discharge header 219, an oxidizing gas (air) supply header 221, and an oxidizing gas discharge header 223. The cartridge 203 also includes an upper tube plate 225a, a lower tube plate 225b, an upper insulator 227a, and a lower insulator 227b. In this embodiment, the cartridge 203 has the steam supply header 217, the product hydrogen discharge header 219, the oxidizing gas supply header 221, and the oxidizing gas discharge header 223 arranged as shown in Figure 2, thereby providing a structure in which the supply steam and the oxidizing gas flow in opposite directions inside and outside the cell stack 101. However, this is not necessarily required. For example, the flow may be parallel inside and outside the cell stack 101, or the oxidizing gas may flow in a direction perpendicular to the longitudinal direction of the cell stack 101.

[0027] The steam electrolysis chamber 215 is a region formed between the upper insulator 227a and the lower insulator 227b. This steam electrolysis chamber 215 is a region in which the electrolysis cells 105 of the cell stack 101 are arranged, and is a region in which hydrogen is produced by electrolyzing steam. The temperature near the center of the longitudinal direction of the cell stack 101 in this steam electrolysis chamber 215 may be monitored by a temperature measurement unit 620 (such as a temperature sensor or a thermocouple). During steady-state operation of the module 201, a high-temperature atmosphere of approximately 700°C to 1000°C is produced.

[0028] The water vapor supply header 217 is an area surrounded by the upper casing 229a and upper tube plate 225a of the cartridge 203, and is connected to the water vapor supply branch pipe 207a by a water vapor supply pipe 231a provided at the top of the upper casing 229a. The multiple cell stacks 101 are joined to the upper tube plate 225a by an upper seal member 237a, and the water vapor supply header 217 guides water vapor supplied from the water vapor supply branch pipe 207a via the water vapor supply pipe 231a into the interiors of the base tubes 103 of the multiple cell stacks 101 at a substantially uniform flow rate, thereby substantially uniforming the hydrogen generation performance of the multiple cell stacks 101.

[0029] The produced hydrogen discharge header 219 is an area surrounded by the lower casing 229b and lower tube plate 225b of the cartridge 203, and is connected to the produced hydrogen discharge branch pipe 209a by a produced hydrogen discharge pipe 231b provided in the lower casing 229b. The multiple cell stacks 101 are joined to the lower tube plate 225b by a lower seal member 237b, and the produced hydrogen discharge header 219 collects the produced hydrogen that passes through the insides of the base tubes 103 of the multiple cell stacks 101 and is supplied to the produced hydrogen discharge header 219, and leads it to the produced hydrogen discharge branch pipe 209a via the produced hydrogen discharge pipe 231b.

[0030] An oxidizing gas supply header (not shown) branches into oxidizing gas supply branch pipes (not shown) at a predetermined flow rate corresponding to the operating temperature of the module 201, and supplies the oxidizing gas to the plurality of cartridges 203. The oxidizing gas supply header 221 is an area surrounded by the lower casing 229b, lower tube plate 225b, and lower heat insulator 227b of the cartridge 203, and is connected to an oxidizing gas supply branch pipe (not shown) by an oxidizing gas supply pipe 233a provided on the side surface of the lower casing 229b. The oxidizing gas supply header 221 guides the oxidizing gas at a predetermined flow rate, supplied from the oxidizing gas supply branch pipe (not shown) via the oxidizing gas supply pipe 233a, to the steam electrolysis chamber 215 via a lower oxidizing gas penetration 235a (described later).

[0031] The oxidizing gas discharge header 223 is an area surrounded by the upper casing 229a, upper tube plate 225a, and upper heat insulator 227a of the cartridge 203, and is connected to an oxidizing gas discharge branch pipe (not shown) by an oxidizing gas discharge pipe 233b provided on the side surface of the upper casing 229a. The oxidizing gas discharge header 223 guides the exhaust oxidizing gas supplied to the oxidizing gas discharge header 223 from the steam electrolysis chamber 215 via an oxidizing gas upper penetration 235b (described later) to the oxidizing gas discharge branch pipe (not shown) via the oxidizing gas discharge pipe 233b.

[0032] The upper tube plate 225a is fixed to the side plate of the upper casing 229a between the top plate of the upper casing 229a and the upper insulator 227a so that the upper tube plate 225a, the top plate of the upper casing 229a, and the upper insulator 227a are approximately parallel to each other. The upper tube plate 225a has a number of holes corresponding to the number of cell stacks 101 provided in the cartridge 203, and the cell stacks 101 are inserted into the holes. The upper tube plate 225a airtightly supports one end of the multiple cell stacks 101 via either or both of an upper seal member 237a and an adhesive member, and also isolates the steam supply header 217 from the oxidizing gas discharge header 223.

[0033] The upper heat insulator 227a is disposed at the lower end of the upper casing 229a so that the upper heat insulator 227a, the top plate of the upper casing 229a, and the upper tube plate 225a are substantially parallel, and is fixed to the side plate of the upper casing 229a. The upper heat insulator 227a has a plurality of holes formed therein corresponding to the number of cell stacks 101 provided in the cartridge 203. The diameters of the holes are set larger than the outer diameters of the cell stacks 101. The upper heat insulator 227a has upper oxidizing gas penetrations 235b formed between the inner surfaces of the holes and the outer surfaces of the cell stacks 101 inserted through the upper heat insulator 227a.

[0034] The upper heat insulator 227a separates the steam electrolysis chamber 215 from the oxidizing gas discharge header 223, and prevents the atmosphere surrounding the upper tube sheet 225a from becoming hot, thereby reducing its strength and increasing corrosion caused by the oxidizing agent contained in the oxidizing gas. To prevent thermal deformation of the upper tube sheet 225a and other components due to temperature differences when the upper tube sheet 225a and other components are exposed to high temperatures within the steam electrolysis chamber 215, a metal material with high temperature resistance, such as a Ni-based alloy, may be used. The upper heat insulator 227a guides the exhaust oxidizing gas, which has been exposed to high temperatures after passing through the steam electrolysis chamber 215, through the upper oxidizing gas penetration 235b and into the oxidizing gas discharge header 223.

[0035] According to this embodiment, the structure of the cartridge 203 described above allows the supply steam and the oxidizing gas to flow in opposite directions between the inside and outside of the cell stack 101. As a result, heat exchange occurs between the exhaust oxidizing gas and the steam supplied to the steam electrolysis chamber 215 through the interior of the base tube 103, and the exhaust oxidizing gas is cooled to a temperature that prevents damage due to stress to the upper tube plate 225a, etc., made of a metallic material, and is then supplied to the oxidizing gas discharge header 223. The supply steam is heated by heat exchange with the exhaust oxidizing gas discharged from the steam electrolysis chamber 215 and is then supplied to the steam electrolysis chamber 215. As a result, steam preheated to a temperature required for the electrolysis reaction can be supplied to the steam electrolysis chamber 215 without using a heater or the like.

[0036] The lower tube sheet 225b is fixed to the side plate of the lower casing 229b between the bottom plate of the lower casing 229b and the lower insulator 227b so that the lower tube sheet 225b, the bottom plate of the lower casing 229b, and the lower insulator 227b are approximately parallel to each other. The lower tube sheet 225b also has a plurality of holes corresponding to the number of cell stacks 101 provided in the cartridge 203, and the cell stacks 101 are inserted into the holes. The lower tube sheet 225b airtightly supports the other ends of the plurality of cell stacks 101 via either or both of a lower seal member 237b and an adhesive member, and also isolates the produced hydrogen discharge header 219 from the oxidizing gas supply header 221.

[0037] The lower heat insulator 227b is disposed at the upper end of the lower casing 229b so that the lower heat insulator 227b, the bottom plate of the lower casing 229b, and the lower tube plate 225b are substantially parallel, and is fixed to the side plate of the lower casing 229b. The lower heat insulator 227b has a plurality of holes formed therein corresponding to the number of cell stacks 101 provided in the cartridge 203. The diameters of the holes are set larger than the outer diameters of the cell stacks 101. The lower heat insulator 227b has lower oxidizing gas penetrations 235a formed between the inner surfaces of the holes and the outer surfaces of the cell stacks 101 inserted through the lower heat insulator 227b.

[0038] The lower heat insulator 227b separates the steam electrolysis chamber 215 from the oxidizing gas supply header 221, and prevents the atmosphere surrounding the lower tube sheet 225b from becoming too hot, thereby reducing its strength and increasing corrosion caused by the oxidizing agent contained in the oxidizing gas. To prevent thermal deformation of the lower tube sheet 225b and other components due to temperature differences when the lower tube sheet 225b and other components are exposed to the high temperatures within the steam electrolysis chamber 215, a metal material with high temperature resistance, such as a Ni-based alloy, may be used. The lower heat insulator 227b guides the oxidizing gas supplied to the oxidizing gas supply header 221 through the lower oxidizing gas penetration 235a to the steam electrolysis chamber 215.

[0039] According to this embodiment, the structure of the cartridge 203 described above allows the product hydrogen and the oxidizing gas to flow in opposite directions between the inside and outside of the cell stack 101. As a result, the product hydrogen that passes through the interior of the base tube 103 and the steam electrolysis chamber 215 exchanges heat with the oxidizing gas supplied to the steam electrolysis chamber 215, and is cooled to a temperature that prevents damage due to stress to the lower tube plate 225b, which is made of a metal material, and is supplied to the product hydrogen discharge header 219. The oxidizing gas is heated by heat exchange with the product hydrogen and is supplied to the steam electrolysis chamber 215. As a result, the oxidizing gas heated to a temperature required for the electrolysis reaction can be supplied to the steam electrolysis chamber 215 without using a heater or the like.

[0040] 3 , the module (electrolysis cell module) 201 includes, for example, a plurality of cartridges (electrolysis cell cartridges) 203, a module container 205 that houses the plurality of cartridges 203, and a heat insulator 204 that is provided inside the module container 205 and insulates the plurality of cartridges 203. The module 201 includes a water vapor supply header 207, a plurality of water vapor supply branch pipes 207a, a produced hydrogen discharge header 209, and a plurality of produced hydrogen discharge branch pipes 209a. The module 201 also includes an oxidizing gas supply header (not shown) and a plurality of oxidizing gas supply branch pipes (not shown).

[0041] The steam supply header 207 is provided inside the module container 205 and is connected to a steam supply unit that supplies steam at a predetermined gas composition and a predetermined flow rate corresponding to the amount of hydrogen generated by the module 201, and is also connected to multiple steam supply branch pipes 207a. This steam supply header 207 branches and guides the steam at a predetermined flow rate supplied from the steam supply unit to multiple steam supply branch pipes 207a. The steam supply branch pipes 207a are connected to the steam supply header 207 and are also connected to steam supply pipes 231a of the multiple cartridges 203. This steam supply branch pipe 207a guides the steam supplied from the steam supply header 207 to the multiple cartridges 203 at a substantially uniform flow rate, thereby substantially uniforming the electrolysis voltage of the multiple cartridges 203.

[0042] The produced hydrogen discharge branch pipe 209a is connected to the produced hydrogen discharge pipes 231b of the multiple cartridges 203 and is also connected to the produced hydrogen discharge mother pipe 209. This produced hydrogen discharge branch pipe 209a guides the produced hydrogen discharged from the cartridges 203 to the produced hydrogen discharge mother pipe 209. The produced hydrogen discharge mother pipe 209 is connected to the multiple produced hydrogen discharge branch pipes 209a and is partially disposed outside the module container 205. This produced hydrogen discharge mother pipe 209 guides the produced hydrogen discharged at a substantially uniform flow rate from the produced hydrogen discharge branch pipe 209a to the outside of the module container 205.

[0043] The module container 205 is operated with an internal pressure of atmospheric pressure to several MPa and a surface temperature of atmospheric temperature to approximately 300° C., and is preferably made of carbon steel, for example, from the viewpoint of cost reduction.

[0044] Here, in this embodiment, a configuration in which multiple cartridges 203 are grouped together and stored in a module container 205 is described, but this is not limited to this, and for example, a configuration in which the cartridges 203 are not grouped together but are stored in a module container 205 is also possible.

[0045] The DC power required for the electrolysis reaction is converted to a predetermined voltage by a power converter such as a power conditioner and then supplied to the module. The power supplied to the module is distributed according to the number of cartridges connected in series and in parallel. In each cartridge 203, power is supplied to a power supply member (not shown) via a power supply plate (not shown), and is then passed to the vicinity of the end of the cell stack 101 via lead films 117 made of Ni / YSZ or the like provided on the multiple electrolysis cells 105, before being supplied to the electrolysis cells.

[0046] Hereinafter, a hydrogen production system according to an embodiment of the present disclosure will be described with reference to the drawings. The embodiment described below shows one aspect of the present disclosure, and is not intended to limit the present disclosure. The present disclosure can be modified as desired within the scope of the technical concept of the present disclosure.

[0047] <Configuration of the Hydrogen Production System According to the Present Disclosure> Next, a hydrogen production system according to the present disclosure will be described with reference to FIG. 4 . The SOEC hydrogen production system (high-temperature steam electrolysis system, electrolysis system) 310 according to the present disclosure shown in FIG. 4 is an example of a pressurized solid oxide electrolysis cell (pressurized SOEC) system. The system includes an electrolytic cell 105 that electrolyzes water vapor, a power supply 650 that applies voltage to the electrolytic cell 105, and an excess heat recovery system including a steam generator 343 that recovers excess heat generated by the electrolytic cell and generates and heats the water vapor supplied to the electrolytic cell 105, a product hydrogen cooler 411, an oxidizing gas cooler 512, and the like. The excess heat will be described later. The electrolytic cell 105 includes a hydrogen electrode 109, an oxygen electrode 113, and a solid electrolyte membrane 111 disposed between the hydrogen electrode 109 and the oxygen electrode 113. Although FIG. 4 schematically illustrates only one electrolytic cell 105, multiple electrolytic cells 105 may be housed in a module container 205. The power supply 650 is configured to apply a voltage between the hydrogen electrode 109 and the oxygen electrode 113 .

[0048] The hydrogen electrode 109 is connected to a steam supply header 207 through which steam supplied to the hydrogen electrode 109 flows, and a produced hydrogen discharge header 209 through which steam discharged from the hydrogen electrode 109 flows. The steam supply header 207 is connected to a water supply line 340 via a raw material gas supply line 346 and a steam supply line 344, and a water supply pump 341 is provided on the water supply line 340. A flow rate adjustment valve 342 (or a flow rate adjustment device) that controls the water supply flow rate is provided downstream of the water supply pump 341. A steam generator 343 is connected to the steam supply line 344 in series with the flow rate adjustment valve 342.

[0049] The steam supply line 344 is connected to a product hydrogen recirculation line 415, and the steam (feedstock) is combined with a portion of the recycled product hydrogen. If superheating is required, the steam passes through a feed gas superheater provided in the feed gas supply line 346 and is supplied to the hydrogen electrode 109 in the module 201. The hydrogen generated at the hydrogen electrode 109 is extracted through a product hydrogen discharge line 410, which is provided with a product hydrogen cooler 411. Downstream of the product hydrogen cooler 411 is a branch point to a product hydrogen recirculation line 415, which recirculates a portion of the produced hydrogen to the feed gas supply line 346. The product hydrogen recirculation line 415 is provided with a recirculation blower 412 and a recirculation blower motor 413 that can adjust the recirculation flow rate. The recirculation equipment is not limited to a blower.

[0050] A produced hydrogen / oxidizing gas differential pressure control valve 414 is provided downstream of the produced hydrogen discharge line 410, which branches off from the produced hydrogen recirculation line 415, to control the differential pressure between the hydrogen electrode 109 and the oxygen electrode 113 of the module 201. A produced hydrogen cooler 417 is provided downstream of the produced hydrogen / oxidizing gas differential pressure control valve 414, and the hydrogen is cooled to a predetermined temperature or dehumidified as necessary, and then supplied as cooled hydrogen via a cooled hydrogen line 416. A flow meter (flow rate measuring device) 640 is provided in the cooled hydrogen line 416.

[0051] The oxygen electrode 113 is connected to an oxidizing gas supply line 513 through which an oxidizing gas (e.g., air) containing oxygen that is supplied to the oxygen electrode 113 flows, and an oxidizing gas discharge line 514 through which the oxidizing gas exhaust gas discharged from the oxygen electrode 113 flows. The oxidizing gas intake line 510 is equipped with an oxidizing gas compressor 511 that compresses the oxidizing gas and an oxidizing gas cooler 512 that cools the pressurized oxidizing gas. The oxidizing gas intake line 510 is connected to the oxidizing gas supply line 513 and supplies oxidizing gas at a desired temperature, pressure, and flow rate to the module 201. A steam generator 343 is provided in the oxidizing gas discharge line 514 and is connected to an expander (power turbine) 515 that is driven by the exhaust oxidizing gas after heat recovery. A motor / generator 518 is connected to the expander 515. The exhaust oxidizing gas whose power has been recovered by the expander 515 passes through an exhaust oxidizing gas discharge line 516 and is discharged to the outside from a vent stack 517 .

[0052] <Operation (Operating Method) of the Hydrogen Production System According to the Present Disclosure> Next, the operation (operating method) of the hydrogen production system according to an embodiment of the present disclosure will be described. Water from a water supply source is circulated through a water supply line 340 by a water supply pump 341 and heated in a steam generator 343 by the operation described below to produce pressurized steam. The amount of water supply is determined based on the system steam utilization rate Uss, which is the ratio of the amount of steam electrolyzed to the amount of water (steam) supplied from outside the electrolysis system. The pressurized steam generated in the steam generator 343 flows through a steam supply line 344, merges with recirculated gas supplied via a produced hydrogen recirculation line 415, and is supplied to the hydrogen electrode 109. By recycling and merging a portion of the produced hydrogen with the supplied steam, a portion of the produced hydrogen is included in the feed gas, which prevents oxidation of metals on the feed gas supply line 346 and the hydrogen electrode side of the module 201. Furthermore, by adjusting the recirculated gas flow rate, the module steam utilization rate Usm in the electrolysis reaction can be adjusted to a desired state. Here, the module water vapor utilization rate Usm is the ratio of the amount of water vapor electrolyzed to the amount of water vapor supplied to the hydrogen electrode 109. Meanwhile, the oxidizing gas compressed by the oxidizing gas compressor 511 is adjusted to a desired temperature in an oxidizing gas cooler 512 provided in the oxidizing gas intake line 510, and then flows through an oxidizing gas supply line 513 and is supplied to the oxygen electrode 113, thereby maintaining the operating temperature of the water vapor electrolysis chamber 215 at an appropriate value.

[0053] When the power supply 650 applies a DC voltage between the hydrogen electrode 109 and the oxygen electrode 113, the water vapor in the hydrogen electrode 109 is electrolyzed to generate hydrogen and oxygen ions (O2-) (see reaction formula (1) below). The oxygen ions pass through the solid electrolyte membrane 111 and become oxygen at the oxygen electrode 113 (see reaction formula (2) below). The produced hydrogen flowing out from the hydrogen electrode 109 contains water vapor, and the hydrogen-containing water vapor flows through the produced hydrogen discharge line 410 and into the produced hydrogen cooler 411. In the produced hydrogen cooler 411, the water vapor in the produced hydrogen is cooled so that it does not condense and its temperature is below the heat resistance temperature of the recirculation blower 412. The produced hydrogen / oxidizing gas differential pressure control valve 414 controls the differential pressure between the hydrogen electrode 109 and the oxygen electrode 113, measured by the differential pressure gauge 630, to be below a predetermined value (e.g., 1 kPa). Furthermore, the hydrogen is cooled to a predetermined supply temperature by a product hydrogen cooler 417 installed downstream of the product hydrogen / oxidizing gas differential pressure control valve 414 and supplied as cooled hydrogen. If moisture needs to be removed, the product hydrogen cooler 417 may be used as a condenser to separate water and hydrogen into gas and liquid. The water separated by the condenser may be discharged or reused for steam supply. The hydrogen is sent to a hydrogen consumption facility or a hydrogen storage device (not shown). The oxidizing gas discharge line 514 is connected to the heating side line of the steam generator 343 and is used as a heating medium for the steam generator 343. Since the heat-recovered exhaust oxidizing gas is in a pressurized state, it is supplied to an expander (power turbine) 515, where power is recovered to drive the oxidizing gas compressor, thereby reducing power consumption. H2O + 2e- → H2 + O2- ... (1) 2O2- → O2 + 4e- ... (2)

[0054] Next, the excess heat of the electrolysis reaction will be explained. Because water electrolysis is an endothermic reaction, the amount of heat absorbed by the electrolysis cell 105 increases as the current density increases. On the other hand, increasing the current density also increases the amount of heat generated by internal resistance, such as ohmic losses, in the electrolysis cell 105. The state in which these two factors are balanced is the thermal neutral point. The voltage applied from the power supply 650 to achieve this thermal neutral point is the thermal neutral voltage, which tends to increase slightly with increasing temperature but is approximately 1.3 V. The voltage applied from the power supply 650 to the electrolysis cell 105 is the electrolysis voltage, which is expressed as the average voltage of the electrolysis cell 105. To maintain high hydrogen conversion efficiency in the SOEC hydrogen production system 310, a low electrolysis voltage (close to the thermal neutral voltage) is generally preferable.

[0055] The voltage applied between the hydrogen electrode 109 and the oxygen electrode 113 from the power supply 650 can be set to a voltage greater than the thermoneutral voltage, preferably 0.05 V to 0.5 V higher than the thermoneutral voltage, and more preferably 0.05 V to 0.3 V higher. This causes excess heat to be generated from the electrolytic cell 105, equivalent to the applied voltage minus the thermoneutral voltage. This excess heat is the aforementioned excess heat. To maintain a constant operating temperature by extracting the excess heat to the outside, heat recovery is performed using the feed gas and oxidizing gas supplied to the module 201 while the SOEC hydrogen production system 310 is in operation. The excess heat generated from the electrolytic cell 105 can be extracted to the outside of the module when the temperature of the product hydrogen containing water vapor and the waste oxidizing gas rises above the supply temperature. This allows the excess heat from the electrolytic reaction to be used as a heat source for the steam generator or to heat the feed gas.

[0056] In this way, by providing at least a part of the heat required for generating steam with surplus heat generated during electrolysis of steam in the electrolytic cell 105, it is possible to reduce or eliminate the need for energy supplied from an external source to an electric boiler or heater for generating steam. Furthermore, it is possible to eliminate the need for additional equipment such as an electric boiler and associated equipment such as a heat exchanger, thereby reducing the equipment costs and operating costs of the high-temperature steam electrolysis system (SOEC hydrogen production system) 310.

[0057] The control device 610 controls each shutoff valve and each flow rate adjustment valve based on measurement values ​​of a pressure gauge, a thermometer, a flow meter, and the like provided in the high-temperature steam electrolysis system (SOEC hydrogen production system) 310. The control device 610 is configured, for example, with a central processing unit (CPU), a random access memory (RAM), a read-only memory (ROM), and a computer-readable storage medium. A series of processes for realizing various functions is stored in a storage medium or the like in the form of a program, for example. The CPU reads this program into the RAM or the like and executes information processing and arithmetic operations to realize various functions. The program may be pre-installed in a ROM or other storage medium, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. The computer-readable storage medium includes a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, and the like.

[0058] When the above-described SOEC hydrogen production system 310 is cold-started (started from a low-temperature state of the cartridge 203, such as when the system is stopped), the cell voltage of the cartridge 203 tends to peak at a relatively low temperature range from room temperature to several hundred degrees Celsius, compared to the normal electrolysis voltage. This is because the resistance of the solid electrolyte is high in the low temperature range. Therefore, the cell voltage is highest at the beginning of startup when the cell resistance is high, and then decreases as the temperature rises after reaching its peak.

[0059] The internal heat generated by passing current for electrolysis can be used to heat up the cartridge 203. To shorten the time it takes to heat up, it is necessary to pass a current of a certain level or more to promote internal heat generation. For this reason, the voltage supplied to the cartridge 203 reaches its highest peak at the beginning of a cold start, as described above.

[0060] Power is supplied to the cartridge 203 via a rectifier 60, which will be described later. The rectifier 60 must be operated at an output voltage equal to or lower than the allowable output voltage (maximum operable voltage) as a device specification. In particular, the current supplied from the rectifier 60 to the cartridge 203 must be managed so that the output voltage does not exceed the allowable output voltage even during peak voltages at the beginning of a cold start.

[0061] Limiting the number of cartridges 203 connected in series can reduce the output voltage of the rectifier 60. However, if the number of cartridges 203 connected in series is limited without changing the capacity of the entire system, it is necessary to increase the number of cartridges 203 connected in parallel per rectifier 60, and the current supplied from each rectifier 60 to the cartridges 203 also increases, so in order to operate each rectifier 60 at or below its allowable output current (maximum operable current), it is necessary to increase the number of rectifiers 60.

[0062] Since the temperature inside each cartridge 203 varies depending on the resistance of the cartridge 203, increasing the number of cartridges 203 connected in parallel per rectifier 60 makes it more likely that the temperature distribution inside each cartridge 203 will vary, which may increase the imbalance in current distribution between each cartridge 203.

[0063] As described above, due to the I-V characteristic that has a peak voltage at the beginning of a cold start, and due to the characteristics of the series connection and the parallel connection, the maximum rating of the rectifier 60 during normal electrolysis operation, which is determined by the product of the allowable output voltage and the allowable output current, cannot be fully utilized, resulting in an increase in the number of rectifiers 60 required.

[0064] In response to these issues, in the present disclosure, the control device 50 performs control to switch between parallel connection and series connection. When a predetermined switching condition is not satisfied, the control device 50 switches the power supply circuit 30 so that the cartridges 203 are connected in parallel, and when the predetermined switching condition is satisfied, the control device 50 switches the power supply circuit 30 so that the cartridges 203 are connected in series.

[0065] 5 is a diagram illustrating an example of a hardware configuration of a control device according to some embodiments of the present disclosure. As shown in FIG. 5 , the control device (Controller) 50 is a computer system including, for example, a CPU (Central Processing Unit: Processor) 1100, a secondary storage device (ROM, Secondary storage: Memory) 1200, a main storage device (RAM, Main Memory) 1300, a hard disk drive (HDD) 1400 as a large-capacity storage device, and a communication unit 1500 for connecting to a network or the like. A solid-state drive (SSD) may also be used as the large-capacity storage device. These units are connected via a bus 1800.

[0066] The CPU 1100 controls the entire control device 50 using, for example, an operating system (OS) stored in a secondary storage device 1200 connected via a bus 1800, and executes various processes by executing various programs stored in the secondary storage device 1200. One or more CPUs 1100 may be provided, and they may cooperate with each other to realize processes.

[0067] The main memory device 1300 is composed of writable memory such as cache memory or RAM (Random Access Memory), and is used as a working area for reading out programs executed by the CPU 1100 and writing data processed by the programs.

[0068] The secondary storage device 1200 is a non-transitory computer-readable storage medium. The secondary storage device 1200 is, for example, a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, or a semiconductor memory. Examples of the secondary storage device 1200 include a read-only memory (ROM), a hard disk drive (HDD), a solid state drive (SSD), and a flash memory. The secondary storage device 1200 stores, for example, an OS for controlling the entire information processing device, such as Windows (registered trademark), iOS (registered trademark), or Android (registered trademark), a BIOS (Basic Input / Output System), various device drivers for operating peripheral devices, various application software, and various data and files. The secondary storage device 1200 stores programs for implementing various processes and various data required for implementing various processes. A plurality of secondary storage devices 1200 may be provided, and the above-mentioned programs and data may be stored separately in each secondary storage device 1200.

[0069] The control device 50 may include an input unit such as a keyboard or a mouse, a display unit such as a liquid crystal display device that displays data, etc. The control device 50 may also include a notification unit such as a speaker that includes the display unit and outputs a lamp, sound, especially an alarm sound.

[0070] As described above, the control device 50 in some embodiments of the present disclosure controls switching between parallel connection and series connection of the cartridges 203 .

[0071] A series of processes for realizing the functions of the control device 50 is stored in the form of a program in the secondary storage device 1200 (see FIG. 5), for example, and the CPU (processor) 1100 (see FIG. 5) reads this program into the main storage device 1300 (see FIG. 5) and executes information processing and arithmetic processing to realize various functions. The program may be pre-installed in the secondary storage device 1200, provided in a state stored in another non-transitory computer-readable storage medium, or distributed via wired or wireless communication means. Examples of non-transitory computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0072] FIG. 6 is a circuit diagram showing a parallel connection in some embodiments of the present disclosure. FIG. 7 is a circuit diagram showing a series connection in some embodiments of the present disclosure. In FIGS. 6 and 7 , the number of electrolysis devices (exemplified by cartridges 203A and 203B in FIGS. 6 and 7 ; hereinafter, 203A and 203B may be collectively referred to as cartridge 203) is two, and the number of rectifiers 60 is one. However, this is merely an example, and the number of electrolysis devices (cartridges 203) may be two or more, and the number of rectifiers 60 may be one or more. As shown in FIGS. 6 and 7 , the electrolysis device does not have to be a cartridge unit, but may be a cartridge group in which a plurality of cartridges 203 are electrically connected in series or in parallel, a SOEC module containing cartridges 203, or an electrolysis device in which a plurality of electrolysis cell stacks formed by stacking flat-plate cells are electrically connected in series or in parallel. In the following, the cartridges 203 (203A, 203B) shown in FIGS. 6 and 7 will be described as an electrolysis device, but the present invention is not limited thereto.

[0073] 6 and 7 , the cartridges 203A and 203B and the rectifier 60 are connected via a power supply circuit 30. The power supply circuit 30 is provided with switches 21, 22, 23, 24, and 25. The control device 50 controls the ON / OFF of the switches 21, 22, 23, 24, and 25 to change the path of the power supply circuit 30 and switch between the parallel connection and the series connection of the cartridges 203A and 203B.

[0074] In the case of a parallel connection, the control device 50 turns on the switches 21, 22, 23 and 24 and turns off the switch 25 as shown in FIG.

[0075] In the case of a series connection, the control device 50 turns on the switches 21, 24 and 25 and turns off the switches 22 and 23 as shown in FIG.

[0076] Next, the flow of switching control using the control device 50 will be described. FIG. 8 is a diagram showing the relationship between current, voltage, and cell temperature. In the upper diagram of FIG. 8, the vertical axis represents voltage (V) and the horizontal axis represents current (A). In the lower diagram of FIG. 8, the vertical axis represents cell temperature (°C) and the horizontal axis represents current (A). The current in FIG. 8 indicates the output current, which is the value of the current flowing through the rectifier 60. The voltage indicates the value of the output voltage of the rectifier 60 when the cartridge 203 is connected in series and in parallel to the rectifier 60. The cell temperature indicates the temperature of the cartridge 203. In the upper and lower diagrams of FIG. 8, the current value on the horizontal axis indicates the same value.

[0077] In the upper diagram of Figure 8, the thick line indicates the relationship between current and voltage during temperature rise when the cartridge 203 (electrolysis device) is connected in parallel to the rectifier 60. The thick dashed line indicates the relationship between current and voltage in a temperature equilibrium state after temperature rise is complete in the case of parallel connection. The solid line indicates the relationship between current and voltage during temperature rise when the cartridge 203 (electrolysis device) is connected in series to the rectifier 60. The dashed line indicates the relationship between current and voltage in a temperature equilibrium state after temperature rise is complete in the case of series connection. In the upper diagram of Figure 8, the two-dot chain line indicates the allowable output voltage of the rectifier 60.

[0078] As shown in the upper diagram of Figure 8, if the cartridges 203 (electrolysis devices) are connected in series, during temperature rise, the cell voltage will peak when the current is I1 and exceed the allowable output voltage of the rectifier 60. Therefore, in the present disclosure, during temperature rise, particularly during temperature rise at the beginning of a cold start, it is determined that the predetermined switching condition is not met, and the cartridges 203 (electrolysis devices) are connected in parallel.

[0079] When starting the SOEC hydrogen production system 310, the control device 50 first turns on switches 21, 22, 23, and 24 of the power supply circuit 30 and turns off switch 25 so that the cartridges 203 are connected in parallel. After the cartridges 203 are heated to a predetermined temperature by external heat input, current is applied at I0. The current is then increased from I0 to I1, and the cartridges 203 are further heated by internal heat generated by the current application. As shown by the bold line in the upper diagram of Figure 8 , in the relatively low temperature range immediately after the start of current application, the electrical resistance of the cells is high, so the cell voltage rises rapidly with increasing current and reaches a peak value at current I1. However, because the cartridges 203 are connected in parallel, the cell voltage is suppressed to be below the allowable output voltage of the rectifier 60.

[0080] Thereafter, the current is increased from I1 to I2 to further increase the temperature of the cartridge 203. In this process, the electrical resistance of the cell decreases as the temperature increases, and therefore the cell voltage of the cartridge 203 decreases as the temperature increases, regardless of the increase in the current value.

[0081] When the control device 50 determines that the current value has increased to I3 and that a predetermined switching condition has been satisfied, it controls the switches 21, 22, 23, 24, and 25 of the power supply circuit 30 to switch so that the cartridge 203 is connected in series. However, because abruptly switching the switches 21, 22, 23, 24, and 25 of the power supply circuit 30 increases the risk of surges and short-circuit accidents, the current value is temporarily set to zero during switching.

[0082] In the upper diagram of Figure 8, when the current reaches I3, the cell voltage during parallel connection is approximately the same as the cell voltage in a temperature equilibrium state. The control device 50 determines that the switching conditions are met and temporarily turns off switches 21, 22, 23, 24, and 25 to cut off the connection and establish no-load. If the cartridge 203 is left unloaded for a long period of time, the electrical resistance will increase due to a drop in cell temperature, so the unloaded period is set to, for example, several seconds. To establish no-load, the current is gradually reduced by the rectifier 60 before the circuit is shut off.

[0083] In the present disclosure, the predetermined switching condition is, for example, that the temperature of the cartridge 203 is equal to or higher than the switching temperature of 600° C. and lower than 850° C. In this case, the temperature of the cartridge 203 may be the average temperature of all the cartridges 203 or the highest temperature of the cartridges 203.

[0084] The switching condition may be that the cell voltage of the cartridge 203 exceeds the peak value and is equal to or lower than a predetermined voltage. In this case, the predetermined voltage may be a value smaller than the allowable output voltage of the rectifier 60 connected to the cartridge 203 via the power supply circuit 30 divided by the number of cartridges 203 connected in parallel.

[0085] Next, the control device 50 switches the switches 21, 22, 23, 24, and 25 of the power supply circuit 30 so that the cartridge 203 is connected in series. That is, the control is performed so that the switches 21, 24, and 25 are turned ON and the switches 22 and 23 are turned OFF. The relationship between current and voltage after switching is shown by the dashed line in the upper diagram of Figure 8, which is the relationship between current and voltage in a temperature equilibrium state in the case of a series connection. Because the cell temperature has already risen, the cell voltage does not peak as shown by the solid line in the upper diagram of Figure 8, and instead the cell voltage increases linearly with an increase in current value, as shown by the dashed line.

[0086] As the current value increases from I0, the cell voltage also increases, and the cell temperature also increases as shown in the lower diagram of Figure 8. After that, the load is increased to the rated operating point. The current value at the rated operating point is defined as I4.

[0087] FIG. 9 is a timing chart showing switching of the power supply circuit. In FIG. 9 , the vertical axis represents current, rectifier output voltage, and cell temperature, and the horizontal axis represents time. Of the curves, the solid line up to time t2 represents the rectifier output voltage (in this embodiment) when the electrolytic devices (cartridges 203) are connected in parallel during startup (cold start) of the SOEC hydrogen production system 310. The dashed line represents the rectifier output voltage (in this embodiment) when the electrolytic devices are connected in series. The two-dot-dashed line represents the current, the one-dot-dashed line represents the cell temperature, and the solid line after time t2 represents the rectifier output voltage (in this embodiment) when the electrolytic devices (cartridges 203) are connected in series after switching. The horizontal straight two-dot-dashed line represents the allowable output voltage of the rectifier 60.

[0088] A cold start is initiated at time t0, and immediately after a predetermined temperature is reached due to external heat input and power is applied to start electrolysis, the cell voltage of the cartridges 203 connected in parallel rises sharply with an increase in current, as shown by the solid line, because the cell temperature is low and the cell resistance is high. Therefore, the output voltage of the rectifier 60 also rises similarly. At this time, the cell temperature is, for example, 500 to 600 degrees. The current also gradually increases.

[0089] At time t1, the rectifier output voltage reaches its peak. At this time, as shown by the dashed line, the rectifier output voltage at cold start exceeds the allowable output voltage of the rectifier 60 when the electrolytic devices are connected in series. However, in this embodiment, the electrolytic devices are connected in parallel, so the rectifier output voltage is suppressed to below the allowable rectifier output voltage, as shown by the solid line. After time t1, the cell temperature increases and the electrical resistance of the cells decreases, so the cell voltage, i.e., the rectifier output voltage, gradually decreases despite the increase in current.

[0090] As time t2 approaches, the cell temperature reaches the switching temperature, which is the switching condition. The control device 50 determines that the switching condition is met, and at time t2, temporarily turns off all of the switches 21, 22, 23, 24, and 25 of the power supply circuit 30, creating no load. This temporarily reduces the output voltage and output current of the rectifier 60 to zero. The control device 50 then turns on the switches 21, 24, and 25 of the power supply circuit 30, and turns off the switches 22 and 23, connecting the cartridge 203 in series.

[0091] Thereafter, the cell voltage and cell current, i.e., the output voltage, output current and cell temperature of the rectifier 60, gradually increase and reach the rated operating point at time t3.

[0092] The above describes a cold start in which the SOEC hydrogen production system 310 is started up when the temperature (cell temperature) of the electrolysis device (cartridge 203) is low. However, in the case of a hot start in which the cell temperature is high, such as when the system is started (restarted) after an emergency shutdown, if the cell temperature is higher than a predetermined temperature, the control device 50 determines that the predetermined condition is met, and turns on switches 21, 24, and 25 of the power supply circuit 30, turns off switches 22 and 23, and energizes the cartridge 203 in series. The predetermined temperature is the switching temperature for the switching condition described above, and is, for example, equal to or higher than 600°C and lower than 850°C.

[0093] <Additional Notes> The control device, electrolysis system, control method, and control program described in the above-described embodiments can be understood, for example, as follows.

[0094] The control device (50) of the first aspect of the present disclosure is a control device that controls the power supply circuit (30) of the electrolysis device (203), and determines whether or not a predetermined condition is satisfied. If it determines that the condition is not satisfied, the control device (50) switches the power supply circuit (30) so that the electrolysis device is connected in parallel.

[0095] By connecting the electrolysis devices in parallel, the peak voltage of the cell voltage of the electrolysis device can be suppressed so that the cell voltage of the electrolysis device does not exceed the allowable output voltage of the rectifier (60), and there is no need to limit the number of electrolysis devices connected to one rectifier.

[0096] When it is determined that the condition is satisfied, the control device of the second aspect of the present disclosure may perform control to switch the power supply circuit so that the electrolysis device is connected in series.

[0097] When the electrolyzer meets the conditions, the electrolyzer can be switched to the same series connection as in rated operation, allowing the rectifier to perform electrolysis at the appropriate current and voltage at the rated operating point. By reducing the number of parallel connections and increasing the number of series connections, current imbalances can be suppressed.

[0098] In the control device of a third aspect of the present disclosure, in the first or second aspect, the switching condition may be that the temperature of the electrolysis device is equal to or higher than 600 degrees and lower than 850 degrees.

[0099] It is possible to confirm that the electrolysis device has reached its temperature and switch from parallel to series when appropriate.

[0100] In the control device of a fourth aspect of the present disclosure, in the first or second aspect, the switching condition may be that the cell voltage of the electrolysis device has peaked and is equal to or lower than a predetermined voltage.

[0101] By connecting the cells in parallel when the cell voltage of the electrolysis device peaks, the allowable output voltage of the rectifier is not exceeded, and the cell voltage gradually decreases thereafter until it reaches a predetermined voltage or below, confirming that the temperature has risen sufficiently, and then switch from parallel to series connection under appropriate conditions.

[0102] The control device of a fifth aspect of the present disclosure may be configured such that, in the fourth aspect, the predetermined voltage is a value smaller than a value obtained by dividing the allowable output voltage of a rectifier (60) connected to the electrolytic device via the power supply circuit by the number of electrolytic devices connected in parallel.

[0103] It is possible to ensure that the electrolyzer is operated so that the peak cell voltage is below the allowable output voltage of the rectifier.

[0104] In the control device of the sixth aspect of the present disclosure, the electrolytic device may be heated by utilizing internal heat generated by passing current for electrolysis, and the control may be performed when the temperature of the electrolytic device is raised by the electrolysis.

[0105] An electrolysis system (310) according to a seventh aspect of the present disclosure includes a module (201) having a plurality of electrolysis devices, a rectifier, and a control device according to any one of the first to sixth aspects.

[0106] The control method of an eighth aspect of the present disclosure is a control method for controlling a power supply circuit of an electrolysis device, in which a computer determines whether a predetermined condition is satisfied, and if it determines that the condition is not satisfied, switches the power supply circuit so that the electrolysis device is connected in parallel.

[0107] A control program according to a ninth aspect of the present disclosure causes a computer to execute the control method according to the eighth aspect.

[0108] 21, 22, 23, 24, 25 Switch 30 Power supply circuit 50 Control device 60 Rectifier 101 Cell stack 103 Base tube 105 Electrolysis cell (hydrogen generation section) 107 Interconnector 109 Hydrogen electrode (fuel electrode) 111 Solid electrolyte membrane 113 Oxygen electrode 117 Lead membrane 201 Module 203, 203A, 203B Cartridge (electrolysis device) 204 Heat insulating material 205 Module container 207 Steam supply header 207a Steam supply branch pipe 209 Produced hydrogen discharge header 209a Produced hydrogen discharge branch pipe 215 Steam electrolysis chamber (hydrogen generation section) 217 ​​Steam supply header 219 Produced hydrogen discharge header 221 Oxidizing gas supply header 223 Oxidizing gas discharge header 225a Upper tube plate 225b Lower tube plate 227a Upper heat insulator 227b Lower heat insulator 229a Upper casing 229b Lower casing 231a Steam supply pipe 231b Produced hydrogen discharge pipe 233a Oxidizing gas supply pipe 233b Oxidizing gas discharge pipe 235a Oxidizing gas lower penetration 235b Oxidizing gas upper penetration 237a Upper seal member 237b Lower seal member 310 High temperature steam electrolysis system (SOEC hydrogen production system, electrolysis system) 340 Feed water line 341 Feed water pump 342 Flow rate adjustment valve (flow rate adjustment device) 343 Steam generator (including feed water heater) 344 Steam supply line 346 Raw material gas supply line 410 Produced hydrogen discharge line 411 Produced hydrogen cooler 412 Recirculation blower 413 Recirculation blower motor 414 Produced hydrogen / oxidizing gas differential pressure control valve 415 Produced hydrogen recirculation line 416 Cooled hydrogen line 417 Produced hydrogen cooler 510 Oxidizing gas intake line 511 Oxidizing gas compressor 512 Oxidizing gas cooler513 Oxidizing gas supply line 514 Oxidizing gas exhaust line 515 Expander (or power turbine) 516 Exhaust oxidizing gas release line 517 Vent stack 518 Motor / generator 610 Control device 620 Temperature measurement unit 630 Pressure gauge (differential pressure gauge) 640 Flow meter (flow rate measurement device) 650 Power supply unit 1100 CPU 1200 Secondary storage device 1300 Main storage device 1500 Communication unit 1800 Bus

Claims

1. A control device that controls a power supply circuit of an electrolysis device, which determines whether or not a predetermined condition is met, and if it determines that the condition is not met, controls the power supply circuit to switch so that the electrolysis device is connected in parallel.

2. The control device according to claim 1, wherein, when it is determined that the condition is met, the control device performs control to switch the power supply circuit so that the electrolysis device is connected in series.

3. The control device according to claim 1, wherein the condition is that the temperature of the electrolysis device is equal to or greater than 600 degrees and less than 850 degrees.

4. The control device according to claim 1, wherein the condition is that the cell voltage of the electrolysis device has reached its peak and is equal to or lower than a predetermined voltage.

5. The control device according to claim 4, wherein the predetermined voltage is a value smaller than the allowable output voltage of a rectifier connected to the electrolytic device via the power supply circuit divided by the number of electrolytic devices connected in parallel.

6. The control device according to claim 1, wherein the temperature of the electrolytic device is increased by utilizing internal heat generated by energizing the device for electrolysis, and the control is performed when the temperature of the electrolytic device is increased by the electrolysis.

7. An electrolysis system comprising a module having a plurality of electrolysis devices, a rectifier, and the control device according to claim 1.

8. A control method for controlling a power supply circuit of an electrolysis device, the control method comprising: determining whether or not a predetermined condition is satisfied; and, if it is determined that the condition is not satisfied, switching the power supply circuit so that the electrolysis device is connected in parallel, the control method being carried out by a computer.

9. A control program for causing a computer to execute the control method of claim 8.

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