Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/02—Process control or regulation
  • C25B15/021—Process control or regulation of heating or cooling
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/02—Process control or regulation
  • C25B15/023—Measuring, analysing or testing during electrolytic production
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features

Definitions

• This disclosure relates to a control device, an electrolysis system, a control method, and a control program.
• 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.
• Solid oxide electrolysis cells SOECs, hereafter 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 are capable of producing hydrogen with higher efficiency than other electrolysis methods. Co-electrolysis is also possible, in which a mixture 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.
• CO2 carbon dioxide
• RSOCs reversible solid oxide electrochemical cells
• reversible cells Some solid oxide electrolysis cells are being developed as reversible solid oxide electrochemical cells (RSOCs; hereafter referred to as “reversible cells”) that have the two-way functionality of producing hydrogen and oxygen through a reverse reaction when supplied with external electricity and high-temperature steam, and also functioning as a fuel cell to generate electricity.
• electrochemical cell a cell that functions as both a fuel cell cell that generates electricity and an electrolysis cell that performs water electrolysis
• electrochemical cell stack a stack that functions as both a fuel cell stack and an electrolysis cell stack
• the electrolytic cell stack is connected in series or in parallel to the rectifier.
• the electrolytic cell stack is connected in parallel to the rectifier.
• the electrolysis cell stack is connected in parallel to the rectifier, which requires a large current, but the rectifier must be operated at an output current not exceeding its allowable limit, which creates a problem of limitations on the number of parallel connections.
• the electrolysis cell stack is connected in series to the rectifier, for example, when the electrolysis cell stack is energized for electrolysis, and the temperature rises due to internal heat generation, the peak voltage may exceed the allowable output voltage of the rectifier. To prevent this, it is necessary to reduce the voltage supplied to the electrolysis cell stack.
• This disclosure has been made in light of these circumstances, and aims to provide a control device, electrolysis system, control method, and control program that can suppress peak voltage.
• control device that controls the power supply circuit of an electrolytic device, determines whether or not certain conditions are met, and if it determines that the conditions are not met, controls the power supply circuit to switch so that the electrolytic device is connected in parallel.
• the electrolysis system of the present disclosure includes a module having multiple electrolysis devices, a rectifier, and the aforementioned control device.
• the control method disclosed herein is a control method for controlling the power supply circuit of an electrolysis device, in which a computer determines whether 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.
• the control program disclosed herein causes a computer to execute the aforementioned control method.
• the peak voltage of the cell voltage of the electrolysis device can be suppressed.
• FIG. 1 illustrates one aspect of an electrolysis cell stack in some embodiments of the present disclosure.
• FIG. 1 illustrates one aspect of an electrolysis cell cartridge in some embodiments of the present disclosure.
• FIG. 1 illustrates one aspect of a cross-section of an electrolysis cell module in some embodiments of the present disclosure.
• FIG. 1 illustrates an aspect of an electrolysis system according to some embodiments of the present disclosure.
• FIG. 2 is a diagram illustrating an example of a hardware configuration of a control device according to some embodiments of the present disclosure.
• FIG. 1 is a circuit diagram illustrating a parallel connection in some embodiments of the present disclosure.
• FIG. 1 is a circuit diagram illustrating a series connection in some embodiments of the present disclosure.
• FIG. 2 is a diagram showing the relationship between current and cell voltage and cell temperature in some embodiments of the present disclosure.
• FIG. 10 is a diagram showing a timing chart of switching of a power supply circuit in some embodiments of the present disclosure.
• 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 to this, 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 as well.
• the positional relationships of each component described using the terms “above” and “below” with respect to the plane of the paper indicate the vertically upper and lower sides, respectively.
• the vertical direction on the plane of the paper is not necessarily limited to the vertically upper and lower directions, but may also correspond to, for example, the horizontal direction perpendicular to the vertical direction.
• FIG. 1 a cylindrical cell stack using a substrate tube will be described as an example according to this embodiment.
• 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.
• 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.
• 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 of the electrolytic cell 105 at the extreme end in the axial direction of the substrate tube 103 among a plurality of electrolytic cells 105 formed on the outer peripheral surface of the substrate tube 103, and also includes a lead film 117 electrically connected to the hydrogen electrode 109 of the electrolytic cell 105 formed at the other extreme end.
• the gas supplied to and discharged from the hydrogen electrode 109 often contains hydrogen in addition to the water vapor used in electrolysis, but in the following explanation, 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.”
• the substrate tube 103 is made of a porous material, and its main components are, for example, CaO-stabilized ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ + NiO), Y2O3-stabilized ZrO2 (YSZ), or MgAl2O4.
• This substrate tube 103 supports the electrolytic cell 105, interconnector 107, and lead film 117, and also diffuses the supply steam supplied to the inner surface of the substrate tube 103 through the pores in the substrate tube 103 to the hydrogen electrode 109 formed on the outer surface of the substrate tube 103.
• the hydrogen electrode 109 is made of a composite oxide of Ni and a zirconia-based electrolyte material, such as Ni/YSZ, and has a thickness of 50 ⁇ m to 250 ⁇ m.
• the hydrogen electrode 109 may be formed by screen printing a slurry.
• the solid electrolyte membrane 111 is mainly made of YSZ, which has gas-tightness that makes it difficult for gas to pass through and high oxygen ion conductivity at high temperatures. This solid electrolyte membrane 111 moves oxygen ions (O2-) generated at the hydrogen electrode to the oxygen electrode.
• the thickness of the solid electrolyte membrane 111 located on the surface of the hydrogen electrode 109 is 5 ⁇ m to 100 ⁇ m, and the solid electrolyte membrane 111 may be formed by screen-printing a slurry.
• the oxygen electrode 113 is made of, for example, a LaSrMnO3-based oxide or a LaCoO3-based oxide, and a slurry of the oxide is applied to the oxygen electrode 113 by screen printing or 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 LaMnO3.
• 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.
• 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 discharged to the outside together with the oxidizing gas supplied to the oxygen electrode.
• Oxidizing gases are not directly involved in the electrolysis reaction, but they supply the heat necessary for the electrolysis reaction (endothermic) and expel excess heat generated by the electrolysis reaction. They usually contain 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.
• 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.
• M is an alkaline earth metal element
• L is a lanthanoid element
• the interconnector 107 is a dense film that prevents mixing of the supplied water vapor and 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, connecting the adjacent electrolytic cells 105 in series.
• the lead film 117 must be electronically conductive and have a thermal expansion coefficient similar to that of the other materials making up the cell stack 101. Therefore, it is made of a composite of Ni and zirconia-based electrolyte material, such as Ni/YSZ, or M1-xLxTiO3 (M is an alkaline earth metal element, L is a lanthanoid element) such as SrTiO3.
• This lead film 117 applies the DC power required for the electrolysis reaction to the ends of the cell stack 101, to the multiple electrolysis cells 105 connected in series by the interconnectors 107.
• 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.
• Figure 2 shows one embodiment of a solid oxide electrolysis cell (SOEC) cartridge according to this embodiment.
• Figure 3 shows a cross-sectional view of one embodiment of a solid oxide electrolysis cell (SOEC) module according to this embodiment.
• the cartridge 203 comprises multiple cell stacks 101, steam electrolysis chambers 215, a steam supply header 217, a produced hydrogen discharge header 219, an oxidizing gas (air) supply header 221, and an oxidizing gas discharge header 223.
• the cartridge 203 also comprises an upper tube plate 225a, a lower tube plate 225b, an upper insulator 227a, and a lower insulator 227b.
• the cartridge 203 has the steam supply header 217, the produced hydrogen discharge header 219, the oxidizing gas supply header 221, and the oxidizing gas discharge header 223 arranged as shown in FIG. 2, resulting in a structure in which the supply steam and the oxidizing gas flow in opposite directions inside and outside the cell stack 101.
• 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.
• the steam electrolysis chamber 215 is an area formed between the upper insulator 227a and the lower insulator 227b.
• This steam electrolysis chamber 215 is an area where the electrolysis cells 105 of the cell stack 101 are arranged, and is an area where water vapor is electrolyzed to produce hydrogen.
• 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 thermocouple), and during steady-state operation of the module 201, a high-temperature atmosphere of approximately 700°C to 1000°C is created.
• 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 by the upper tube plate 225a and upper seal member 237a, and the water vapor supply header 217 directs water vapor supplied from the water vapor supply branch pipe 207a via the water vapor supply pipe 231a into the interior 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.
• 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 by the lower tube plate 225b and lower seal member 237b, and the produced hydrogen discharge header 219 collects the produced hydrogen that passes through the inside of the base tubes 103 of the multiple cell stacks 101 and is supplied to the produced hydrogen discharge header 219, and directs it to the produced hydrogen discharge branch pipe 209a via the produced hydrogen discharge pipe 231b.
• the oxidizing gas supply main pipe 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 multiple cartridges 203.
• the oxidizing gas supply header 221 is an area surrounded by the lower casing 229b, lower tube plate 225b, and lower 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 of the lower casing 229b.
• This oxidizing gas supply header 221 guides a predetermined flow rate of oxidizing gas supplied from the oxidizing gas supply branch pipe (not shown) via the oxidizing gas supply pipe 233a to the steam electrolysis chamber 215 via the oxidizing gas lower penetration 235a (described below).
• the oxidizing gas discharge header 223 is an area surrounded by the upper casing 229a, upper tube plate 225a, and upper insulation 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 of the upper casing 229a.
• This 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 the oxidizing gas upper penetration 235b (described below) to the oxidizing gas discharge branch pipe (not shown) via the oxidizing gas discharge pipe 233b.
• 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.
• the upper tube plate 225a also has multiple holes corresponding to the number of cell stacks 101 provided in the cartridge 203, and a cell stack 101 is inserted into each of the holes.
• This upper tube plate 225a airtightly supports one end of the multiple cell stacks 101 via either or both of the upper seal member 237a and adhesive member, and also isolates the water vapor supply header 217 and the oxidizing gas discharge header 223.
• the upper insulator 227a is arranged at the lower end of the upper casing 229a so that the upper insulator 227a, the top plate of the upper casing 229a, and the upper tube plate 225a are approximately parallel, and is fixed to the side plate of the upper casing 229a.
• the upper insulator 227a has a number of holes corresponding to the number of cell stacks 101 provided in the cartridge 203. The diameter of these holes is set larger than the outer diameter of the cell stack 101.
• the upper insulator 227a has an upper oxidizing gas penetration 235b formed between the inner surface of this hole and the outer surface of the cell stack 101 inserted into the upper insulator 227a.
• This upper 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 too hot, which could result in a decrease in strength and increased corrosion due to the oxidizing agents contained in the oxidizing gas.
• a metal material with high temperature resistance such as a Ni-based alloy, may be used.
• the upper 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.
• the structure of the cartridge 203 described above allows the supply steam and oxidizing gas to flow in opposite directions inside and outside the cell stack 101.
• heat exchange occurs between the exhaust oxidizing gas and the steam supplied to the steam electrolysis chamber 215 through the inside 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 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 supplied to the steam electrolysis chamber 215.
• steam that has been preheated to the temperature required for the electrolysis reaction can be supplied to the steam electrolysis chamber 215 without using a heater or the like.
• the lower tube plate 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 plate 225b, the bottom plate of the lower casing 229b, and the lower insulator 227b are approximately parallel.
• the lower tube plate 225b also has multiple holes corresponding to the number of cell stacks 101 provided in the cartridge 203, and a cell stack 101 is inserted into each of the holes.
• the lower tube plate 225b airtightly supports the other ends of the multiple cell stacks 101 via either or both of the lower seal member 237b and adhesive member, and also isolates the produced hydrogen discharge header 219 from the oxidizing gas supply header 221.
• the lower insulator 227b is arranged at the upper end of the lower casing 229b so that the lower insulator 227b, the bottom plate of the lower casing 229b, and the lower tube plate 225b are approximately parallel, and is fixed to the side plate of the lower casing 229b.
• the lower insulator 227b has a number of holes corresponding to the number of cell stacks 101 provided in the cartridge 203. The diameter of these holes is set larger than the outer diameter of the cell stack 101.
• the lower insulator 227b has a lower oxidizing gas penetration 235a formed between the inner surface of this hole and the outer surface of the cell stack 101 inserted into the lower insulator 227b.
• This lower 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, which could result in a decrease in strength and increased corrosion due to the oxidizing agent contained in the oxidizing gas.
• a metal material with high temperature resistance such as a Ni-based alloy, may be used.
• the lower insulator 227b guides the oxidizing gas supplied to the oxidizing gas supply header 221 through the lower oxidizing gas penetration 235a and into the steam electrolysis chamber 215.
• the structure of the cartridge 203 described above allows the produced hydrogen and oxidizing gas to flow in opposite directions inside and outside the cell stack 101.
• the produced 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 produced hydrogen discharge header 219.
• the oxidizing gas is heated by heat exchange with the produced hydrogen and is supplied to the steam electrolysis chamber 215.
• oxidizing gas heated to the temperature required for the electrolysis reaction can be supplied to the steam electrolysis chamber 215 without using a heater or the like.
• 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 insulating material 204 that is provided inside the module container 205 and insulates the plurality of cartridges 203.
• the module 201 includes a water vapor supply main pipe 207, a plurality of water vapor supply branch pipes 207a, a produced hydrogen discharge main pipe 209, and a plurality of produced hydrogen discharge branch pipes 209a.
• the module 201 also includes an oxidizing gas supply main pipe (not shown) and a plurality of oxidizing gas supply branch pipes (not shown).
• the steam supply main pipe 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 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 main pipe 207 branches and guides the predetermined flow rate of steam 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 main pipe 207 and are also connected to steam supply pipes 231a of multiple cartridges 203.
• This steam supply branch pipe 207a guides the steam supplied from the steam supply main pipe 207 to the multiple cartridges 203 at a substantially uniform flow rate, thereby substantially equalizing the electrolysis voltage of the multiple cartridges 203.
• 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 main pipe 209.
• This produced hydrogen discharge branch pipe 209a guides the produced hydrogen discharged from the cartridges 203 to the produced hydrogen discharge main pipe 209.
• the produced hydrogen discharge main pipe 209 is connected to the multiple produced hydrogen discharge branch pipes 209a, and a portion of it is located outside the module container 205.
• This produced hydrogen discharge main pipe 209 guides the produced hydrogen, which is discharged at a substantially uniform flow rate from the produced hydrogen discharge branch pipe 209a, to the outside of the module container 205.
• the module container 205 is operated with an internal pressure between atmospheric pressure and several MPa and a surface temperature between atmospheric temperature and approximately 300°C, and is preferably made of materials such as carbon steel from the perspective of low cost.
• 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.
• the cartridges 203 can also be stored in the module container 205 without being grouped together.
• the DC power required for the electrolysis reaction is converted to a specified 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.
• power is supplied to a power supply member (not shown) via a power supply plate (not shown), and is then passed to the electrolysis cells near the ends of the cell stack 101 via lead films 117 made of Ni/YSZ or the like provided on the multiple electrolysis cells 105.
• 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, and includes an electrolytic cell 105 that electrolyzes water vapor, a power supply device 650 that applies voltage to the electrolytic cell 105, and an excess heat recovery system that includes a steam generator 343 that recovers excess heat generated by the electrolytic cell and generates and heats the water vapor to be supplied to the electrolytic cell 105, a product hydrogen cooler 411, an oxidizing gas cooler 512, etc.
• pressurized SOEC pressurized solid oxide electrolysis cell
• the electrolysis cell 105 includes a hydrogen electrode 109, an oxygen electrode 113, and a solid electrolyte membrane 111 provided between the hydrogen electrode 109 and the oxygen electrode 113. Although only one electrolysis cell 105 is schematically illustrated in FIG. 4 , a configuration in which multiple electrolysis cells 105 are housed in the module container 205 may also be used.
• the power supply device 650 is configured to apply a voltage between the hydrogen electrode 109 and the oxygen electrode 113.
• the steam supply header 207 is connected to a water supply line 340 via a raw 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 control valve 342 (or flow control 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 control valve 342.
• the steam supply line 344 is connected to the product hydrogen recirculation line 415, and the steam (feedstock) is combined with a portion of the recycled product hydrogen. If superheating is required, it passes through a feed gas superheater installed in the feed gas supply line 346 and is supplied to the hydrogen electrode 109 in the module 201.
• the hydrogen generated in the hydrogen electrode 109 is extracted through the product hydrogen discharge line 410, which is equipped with a product hydrogen cooler 411. Downstream of the product hydrogen cooler 411 is a branch point with the 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 equipped 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.
• a produced hydrogen/oxidizing gas differential pressure control valve 414 Downstream of the produced hydrogen discharge line 410, which branches off from the produced hydrogen recirculation line 415, is a produced hydrogen/oxidizing gas differential pressure control valve 414 that controls the differential pressure between the hydrogen electrode 109 and the oxygen electrode 113 of the module 201. Downstream of the produced hydrogen/oxidizing gas differential pressure control valve 414 is a produced hydrogen cooler 417, which cools the hydrogen to a predetermined temperature or dehumidifies it as necessary, before supplying it as cooled hydrogen via the cooled hydrogen line 416. A flow meter (flow rate measuring device) 640 is provided on the cooled hydrogen line 416.
• 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 .
• the pressurized steam generated in the steam generator 343 flows through the steam supply line 344, merges with the recycled gas supplied via the produced hydrogen recirculation line 415, and is supplied to the hydrogen electrode 109.
• a portion of the produced hydrogen is contained in the feed gas, which prevents oxidation of the metals in the feed gas supply line 346 and the hydrogen electrode side of the module 201, and by adjusting the flow rate of the recycled gas, the module water vapor utilization rate Usm in the electrolysis reaction can be adjusted to a desired state.
• 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.
• the oxidizing gas compressed by the oxidizing gas compressor 511 is adjusted to the 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 steam electrolysis chamber 215 at an appropriate value.
• 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.
• 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).
• the hydrogen is then cooled to a predetermined supply temperature by a product hydrogen cooler 417 provided 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 the water and hydrogen into gas and liquid. The water separated by the condenser may be discharged or reused for supplying steam.
• 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.
• the heat-recovered exhaust oxidizing gas is pressurized and is supplied to an expander (power turbine) 515, where power is recovered to drive the oxidizing gas compressor, thereby reducing power consumption.
• 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 thermal neutral voltage, preferably 0.05 V to 0.5 V higher than the thermal neutral 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 thermal neutral voltage. This excess heat is the aforementioned excess heat.
• heat is recovered 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 removed from the module when the product hydrogen and waste oxidizing gas containing water vapor rise above the supply temperature. This allows the excess heat from the electrolytic reaction to be used as a heating source for the steam generator or to heat the feed gas.
• the control device 610 controls each shutoff valve and each flow rate adjustment valve based on the measured 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 CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and computer-readable storage media.
• CPU Central Processing Unit
• RAM Random Access Memory
• ROM Read Only Memory
• a series of processes for realizing various functions is stored in a storage medium or the like in the form of a program, and 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.
• Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.
• the cell voltage of cartridge 203 tends to be higher than the normal electrolysis voltage and peak in the relatively low temperature range from room temperature to several hundred degrees. 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 after peaking, it decreases as the temperature rises.
• the internal heat generated by passing electricity through the cartridge 203 for electrolysis can be used to heat it up. To shorten the time it takes to heat up, it is necessary to pass a current above a certain level 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.
• Rectifier 60 must be operated at or below the allowable output voltage (maximum operable voltage) as part of the equipment specifications. In particular, the current supplied from rectifier 60 to cartridge 203 must be managed so that it does not exceed the allowable output voltage, even during peak periods at the beginning of a cold start.
• the output voltage of the rectifier 60 can be reduced.
• 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, which increases the current supplied from each rectifier 60 to the cartridges 203. Therefore, 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.
• each cartridge 203 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 the current distribution between each cartridge 203.
• the rectifiers 60 are unable to fully utilize their maximum rating during normal electrolysis operation, which is determined by the product of the allowable output voltage and the allowable output current, resulting in an increase in the number of rectifiers 60 required.
• the present disclosure provides for the control of switching between parallel and series connections by the control device 50.
• 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 met, the control device 50 switches the power supply circuit 30 so that the cartridges 203 are connected in series.
• FIG. 5 is a diagram illustrating an example of a hardware configuration of a control device according to some embodiments of the present disclosure.
• 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.
• SSD solid-state drive
• the CPU 1100 controls the entire control device 50 using, for example, an OS (Operating System) stored in the secondary storage device 1200 connected via the bus 1800, and executes various processes by running various programs stored in the secondary storage device 1200.
• OS Operating System
• One or more CPUs 1100 may be provided, and they may work together to perform processes.
• 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 programs executed by the CPU 1100 and writing data processed by the programs.
• writable memory such as cache memory or RAM (Random Access Memory)
• Secondary storage device 1200 is a non-transitory computer-readable storage medium. Examples of secondary storage device 1200 include a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, and semiconductor memory. Examples of secondary storage device 1200 include ROM (Read Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), and 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 hardware, 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 the various processes. Multiple secondary storage devices 1200 may be provided, and the above-mentioned programs and data may be stored separately in each secondary storage device 1200.
• the control device 50 may be equipped with an input unit such as a keyboard or mouse, and a display unit such as an LCD display for displaying data. It may also be equipped with a notification unit that includes a display unit and includes a lamp and a speaker that outputs sound, especially an alarm sound.
• an input unit such as a keyboard or mouse
• a display unit such as an LCD display for displaying data. It may also be equipped with a notification unit that includes a display unit and includes a lamp and a speaker that outputs sound, especially an alarm sound.
• control device 50 controls switching between parallel and series connection of the cartridges 203.
• the series of processes for realizing the functions of the control device 50 are stored, for example, in the form of a program in the secondary storage device 1200 (see FIG. 5), 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 operations to realize various functions.
• the program may be pre-installed in the secondary storage device 1200, provided in a state stored on other non-transitory computer-readable storage media, 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.
• FIGS. 6 and 7 are circuit diagrams illustrating parallel and series connections in some embodiments of the present disclosure.
• the number of electrolytic devices illustrated as cartridges 203A and 203B in FIGS. 6 and 7 ; 203A and 203B may hereinafter be collectively referred to as cartridge 203) is two, and the number of rectifiers 60 is one, but this is just an example, and the number of electrolytic devices (cartridges 203) may be two or more, and the number of rectifiers 60 may be one or more.
• the electrolytic 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 electrolytic device in which a plurality of electrolytic cell stacks each having a stack of flat-plate cells are electrically connected in series or in parallel.
• the cartridge 203 (203A, 203B) shown in FIGS. 6 and 7 will be described as an electrolysis device, but the present invention is not limited to this.
• cartridges 203A and 203B and rectifier 60 are connected via power supply circuit 30.
• Power supply circuit 30 is provided with switches 21, 22, 23, 24, and 25. By controlling the ON/OFF of switches 21, 22, 23, 24, and 25, control device 50 changes the path of power supply circuit 30 and switches between parallel and series connections of cartridges 203A and 203B.
• control device 50 When connecting in parallel, the control device 50 turns switches 21, 22, 23, and 24 ON and turns switch 25 OFF, as shown in Figure 6.
• control device 50 When connected in series, the control device 50 turns switches 21, 24, and 25 ON and switches 22 and 23 OFF, as shown in Figure 7.
• FIG. 8 is a diagram showing the relationship between current, voltage, and cell temperature.
• the vertical axis represents voltage (V) and the horizontal axis represents current (A).
• 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.
• the current value on the horizontal axis indicates the same value.
• the thick line shows 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 shows the relationship between current and voltage in a temperature equilibrium state after temperature rise is complete when the cartridge 203 is connected in parallel.
• the solid line shows the relationship between current and voltage during temperature rise when the cartridge 203 (electrolysis device) is connected in series with the rectifier 60.
• the dashed line shows the relationship between current and voltage in a temperature equilibrium state after temperature rise is complete when the cartridge 203 is connected in series.
• the two-dot chain line indicates the allowable output voltage of the rectifier 60.
• the control device 50 When starting up 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 that, after the cartridges 203 have been heated to a predetermined temperature by external heat input, current is started to be supplied at current I0. The current is then increased from I0 to I1, and the cartridges 203 are further heated by internal heat generated by the current supply. 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 supply, the electrical resistance of the cells is high, so the cell voltage rises rapidly as the current increases, reaching a peak value at current I1. However, since the cartridges 203 are connected in parallel, the cell voltage is suppressed to be equal to or lower than the allowable output voltage of the rectifier 60 .
• the current is increased from I1 to I2, further increasing the temperature of cartridge 203.
• the electrical resistance of the cell decreases as the temperature increases, so the cell voltage of cartridge 203 decreases as the temperature increases, regardless of the increase in the current value.
• control device 50 determines that the current value has increased to I3 and that the predetermined switching conditions have been met, 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.
• the device temporarily sets the load to zero during switching, meaning the current value is set to zero.
• 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, cutting off the connection and placing the device in a no-load state. If cartridge 203 is left in a no-load state for a long period of time, the electrical resistance will increase due to a drop in cell temperature, so the no-load period is set to, for example, several seconds.
• the current is gradually reduced by rectifier 60 before the circuit is broken.
• the predetermined switching condition is, for example, that the temperature of the cartridge 203 is equal to or greater than the switching temperature of 600 degrees and less than 850 degrees.
• the temperature of the cartridge 203 may be the average temperature of all the cartridges 203, or the highest temperature of the cartridges 203.
• the switching condition may be that the cell voltage of the cartridge 203 exceeds the peak value and is below a predetermined voltage.
• 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.
• the control device 50 switches switches 21, 22, 23, 24, and 25 of the power supply circuit 30 so that the cartridge 203 is connected in series. That is, it controls switches 21, 24, and 25 to be ON and switches 22 and 23 to be 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, no cell voltage peak occurs as shown by the solid line in the upper diagram of Figure 8, and the cell voltage increases linearly with an increase in current value, as shown by the dashed line.
• the cell voltage also increases, and the cell temperature also increases, as shown in the lower diagram of Figure 8.
• the load is then increased to the rated operating point.
• the current value at the rated operating point is I4.
• FIG. 9 is a diagram showing a time chart for switching the power supply circuit. 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 (this embodiment) when the electrolytic devices (cartridges 203) are connected in parallel at the start-up (cold start) of the SOEC hydrogen production system 310, the dashed line represents the rectifier output voltage (reference example) when the electrolytic devices are connected in series, the two-dot chain line represents current, the one-dot chain line represents cell temperature, and the solid line from time t2 onwards represents the rectifier output voltage (this embodiment) when the electrolytic devices (cartridges 203) are connected in series after switching.
• the horizontal straight dashed double-dashed line indicates the allowable output voltage of the rectifier 60 .
• a cold start is initiated at time t0, and immediately after the cell temperature reaches a predetermined temperature due to external heat input and power is applied to start electrolysis, the cell voltage of the parallel-connected cartridges 203 rises sharply with an increase in current, as shown by the solid line, due to the low cell temperature and high cell resistance. Therefore, the output voltage of the rectifier 60 also rises similarly.
• the cell temperature is, for example, 500 to 600 degrees. The current also gradually increases.
• the rectifier output voltage reaches its peak.
• the electrolytic devices are connected in series during a cold start, so the rectifier output voltage would exceed the allowable output voltage of the rectifier 60.
• the electrolytic devices are connected in parallel, so the rectifier output voltage is kept below the allowable rectifier output voltage, as shown by the solid line.
• the electrical resistance of the cells decreases as the cell temperature rises, so the cell voltage, i.e., the rectifier output voltage, gradually decreases despite an increase in current.
• 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 switches 21, 22, 23, 24, and 25 of the power supply circuit 30, creating no load. As a result, the output voltage and output current of the rectifier 60 temporarily become zero.
• the control device 50 then turns on switches 21, 24, and 25 of the power supply circuit 30, turns off switches 22 and 23, and connects the cartridge 203 in series.
• 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.
• the above describes a cold start in which the SOEC hydrogen production system 310 is started up when the electrolysis device (cartridge 203) temperature (cell temperature) is low.
• the control device 50 determines that the predetermined conditions are met, 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 a series connection.
• the predetermined temperature is the switching temperature for the switching conditions described above, and is, for example, greater than or equal to 600°C and less than 850°C.
• control device electrolysis system, control method, and control program described in the above-described embodiments can be understood, for example, as follows.
• 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), determines whether or not a predetermined condition is met, and if it determines that the condition is not met, controls the power supply circuit (30) to switch so that the electrolysis device is connected in parallel.
• the peak voltage of the cell voltage of the electrolytic devices can be suppressed.
• the cell voltage of the electrolytic devices can be suppressed so as not to exceed the allowable output voltage of the rectifier (60), and there is no need to limit the number of electrolytic devices connected to one rectifier.
• 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.
• the electrolytic device can be switched to the same series connection as for rated operation, allowing the rectifier to perform electrolysis at the appropriate current and voltage at the rated operating point.
• the electrolytic device can be switched to the same series connection as for rated operation, allowing the rectifier to perform electrolysis at the appropriate current and voltage at the rated operating point.
• the switching condition may be that the temperature of the electrolysis device is equal to or greater than 600 degrees and less than 850 degrees.
• 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.
• the predetermined voltage may be a value smaller than the allowable output voltage of the rectifier (60) connected to the electrolytic device via the power supply circuit divided by the number of electrolytic devices connected in parallel.
• the electrolytic device may be heated using 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.
• the electrolysis system (310) of the seventh aspect of the present disclosure includes a module (201) having multiple electrolysis devices, a rectifier, and a control device according to any one of the first to sixth aspects.
• the control method of the 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 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.
• control program of the ninth aspect of the present disclosure causes a computer to execute the control method described in the eighth aspect.

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