ELECTROLYZER SYSTEM INCLUDING INTERNAL MODULE PURGE VENT

Description

FIELD

The present disclosure is generally directed to electrolyzer systems, and specifically to solid oxide electrolyzer cell (SOEC) systems including internal module purge vents and methods of operating the same.

BACKGROUND

In a solid oxide electrolyzer cell (SOEC), a cathode electrode is separated from an anode electrode by a solid oxide electrolyte. When a SOEC is used to produce hydrogen through electrolysis, a positive potential is applied to the air side of the SOEC and oxygen ions are transported from the fuel (e.g., steam) side to the air side. Throughout this specification, the SOEC anode will be referred to as the air electrode, and the SOEC cathode will be referred to as the fuel electrode. During SOEC operation, water (e.g., steam) in the fuel stream is reduced (H₂O+2e⁻→O²⁻+H₂) to form H₂ gas and O²⁻ ions, the O²⁻ ions are transported through the solid electrolyte, and then oxidized (e.g., by an air inlet stream) on the air side (O²⁻ to O₂) to produce molecular oxygen (e.g., oxygen enriched air).

SUMMARY

In various embodiments, an electrolyzer module comprises a hotbox comprising a stack of electrolyzer cells configured receive steam and air, and output a hydrogen product stream and an oxygen exhaust stream during steady-state operation of the electrolyzer module; a product conduit fluidly connecting the hotbox to a product header, and configured to provide the hydrogen product stream from the hotbox to a product header; an exhaust duct fluidly connected to a module exhaust; an air exhaust conduit fluidly connecting the hotbox to the exhaust duct, and configured to provide the oxygen exhaust stream from the hotbox to the exhaust duct; a vent conduit fluidly connecting the product conduit to the exhaust duct; and a vent valve disposed on the vent conduit and configured to control flow of the hydrogen product stream through the vent conduit.

In various embodiments, a method of operating an electrolyzer system includes providing steam and air to a stack of electrolyzer cells located in a first hotbox of a first electrolyzer module, operating the stack in a steady-state mode to generate a hydrogen product stream and an oxygen exhaust stream, to provide the hydrogen product stream from the first hotbox to a product header and to provide the oxygen exhaust stream from the first hotbox to an exhaust duct, and operating the stack in a fault mode by providing both the hydrogen product stream and the oxygen exhaust stream to the exhaust duct.

In various embodiments, a method of operating a solid oxide electrolyzer cell stack comprises providing steam to fuel electrodes of solid oxide electrolyzer cells of the solid oxide electrolyzer cell stack and applying electric power to the stack to electrolyze the steam to generate a hydrogen product stream, wherein the fuel electrodes comprise a nickel cermet; stopping providing the steam to the fuel electrodes; providing air to the fuel electrodes to oxidize the nickel to nickel oxide; and providing hydrogen to the fuel electrodes to reduce the nickel oxide to nickel.

FIGURES

FIG. 1A is a perspective view of a solid oxide electrolyzer cell (SOEC) stack, and FIG. 1B is a side cross-sectional view of a portion of the stack of FIG. 1A.

FIG. 2 is a schematic view of a portion of an electrolyzer system, according to various embodiments of the present disclosure.

FIG. 3 is a schematic view of an electrolyzer module that may be included in the electrolyzer system of FIG. 2.

FIG. 4A is a schematic view of a portion of an electrolyzer system, according to various embodiments of the present disclosure, and FIG. 4B is a schematic view of an electrolyzer module that may be included in the electrolyzer system of FIG. 4A.

FIG. 5 is a perspective view showing components inside of the cabinet of the electrolyzer module of FIG. 4B, according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

The various embodiments will be described in detail with reference to the accompanying drawings. The drawings are not necessarily to scale and are intended to illustrate various features of the invention. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes and are not intended to limit the scope of the invention or the claims.

Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, examples include from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about” or “substantially” it will be understood that the particular value forms another aspect. In some embodiments, a value of “about X” may include values of +/−1% X. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

FIG. 1A is a perspective view of an electrolyzer cell stack 100, such as a solid oxide electrolyzer cell (SOEC) stack, and FIG. 1B is a side cross-sectional view of a portion of the stack 100 of FIG. 1A. Referring to FIGS. 1A and 1B, the stack 100 includes multiple electrolyzer cells (e.g., SOECs) 1 that are separated by interconnects 10, which may also be referred to as gas flow separator plates or bipolar plates. Each electrolyzer cell 1 includes an air electrode 3, an electrolyte 5, such as a solid oxide electrolyte for a SOEC, and a fuel electrode 7. The stack 100 also includes internal fuel riser channels 22.

Each interconnect 10 electrically connects adjacent electrolyzer cells 1 in the stack 100. In particular, an interconnect 10 may electrically connect the fuel electrode 7 of one electrolyzer cell 1 to the air electrode 3 of an adjacent electrolyzer cell 1. FIG. 1B shows that the lower electrolyzer cell 1 is located between two interconnects 10.

Various materials may be used for the air electrode 3, electrolyte 5, and fuel electrode 7. For example, the air electrode 3 may comprise an electrically conductive material, such as an electrically conductive perovskite material, such as lanthanum strontium manganite (LSM). Other conductive perovskites, such as LSCo, etc., or metals, such as Pt, may also be used. The electrolyte 5 may comprise a stabilized zirconia, such as scandia stabilized zirconia (SSZ) or yttria stabilized zirconia (YSZ), yttria-ceria-stabilized zirconia (YCSZ), ytterbia-ceria-scandia-stabilized zirconia (YbCSSZ) or blends thereof. In YbCSSZ, scandia may be present in an amount equal to 9 to 11 mol %, such as 10 mol %, ceria may present in amount greater than 0 and equal to or less than 3 mol %, for example 0.5 mol % to 2.5 mol %, such as 1 mol %, and ytterbia may be present in an amount greater than 0 and equal to or less than 2.5 mol %, for example 0.5 mol % to 2 mol %, such as 1 mol %, as disclosed in U.S. Pat. No. 8,580,456, which is incorporated herein by reference. Alternatively, the electrolyte 5 may comprise another ionically conductive material, such as a doped ceria. The fuel electrode 7 may comprise a cermet comprising a nickel containing phase and a ceramic phase. The nickel containing phase may consist entirely of nickel in a reduced state. The ceramic phase may comprise a stabilized zirconia, such as yttria and/or scandia stabilized zirconia and/or a doped ceria, such as gadolinia, yttria and/or samaria doped ceria. The electrodes and the electrolyte may each comprise one or more sublayers of one or more of the above described materials.

Each interconnect 10 includes fuel ribs 12A that at least partially define fuel channels 8A, and air ribs 12B that at least partially define air channels 8B. The interconnect 10 may operate as a gas-fuel separator that separates a fuel, such as steam, flowing to the fuel electrode 7 of one electrolyzer cell 1 in the stack 100 from oxidant, such as air, flowing to the air electrode 3 of an adjacent electrolyzer cell 1 in the stack 100. At either end of the stack 100, there may be an air end plate or fuel end plate (not shown) for providing air or fuel, respectively, to the end electrode. Alternatively, the air end plate or fuel end plate may comprise the same interconnect structure used throughout the stack.

Each interconnect 10 may be made of or may contain electrically conductive material, such as a metal alloy (e.g., chromium-iron alloy) which has a similar coefficient of thermal expansion to that of the solid oxide electrolyte in the cells (e.g., a difference of 0-10%). For example, the interconnects 10 may comprise a metal (e.g., a chromium-iron alloy, such as 4-6 weight percent iron, optionally 1 or less weight percent yttrium and balance chromium alloy). Alternatively, any other suitable conductive interconnect material, such as stainless steel (e.g., ferritic stainless steel, SS446, SS430, etc.) or iron-chromium alloy (e.g., Crofer^tm 22 APU alloy which contains 20 to 24 wt. % Cr, less than 1 wt. % Mn, Ti and La, and balance Fe,^tm or ZMG^tm 232L alloy which contains 21 to 23 wt. % Cr, 1 wt. % Mn and less than 1 wt. % Si, C, Ni, Al, Zr and La, and balance Fe).

FIG. 2 is a schematic view of a portion of an electrolyzer system 300, according to various embodiments of the present disclosure. Referring to FIG. 2, the system 300 may include multiple fluidly connected modules 200. The modules 200 may comprise electrolyzer modules (e.g., hydrogen generation modules) which generate a hydrogen product from electrolysis of water (e.g., steam). While three modules 200 are shown, the system 300 may include any suitable number of modules 200. The system 300 may include a steam conduit (e.g., a pipe, header or manifold) 230 configured to fluidly connect each module 200 to a steam source 30, a product conduit (e.g., a pipe, header or manifold) 240 configured to fluidly connect each module 200 to a hydrogen processor 40, a hydrogen conduit (e.g., a pipe, header or manifold) 250 configured to fluidly connect a hydrogen storage vessel (e.g., hydrogen tank) 50 to the steam conduit 230, and an exhaust conduit (e.g., a pipe, header or manifold) 270 configured to receive oxygen exhaust from the modules 200. The steam source 30 may comprise any suitable source of steam, such as a building or factory steam source (e.g., external boiler, etc.), which provides byproduct steam to the steam conduit 230, and/or a dedicated steam generator which is part of the system 300. The hydrogen processor 40 may comprise any component which may compress and/or store the hydrogen product, such as a mechanical compressor, an electrochemical hydrogen separator (e.g., a proton exchange membrane), and/or a hydrogen storage vessel.

The system 300 may also include a system controller 225, an optional system recycling conduit 244, an optional vent conduit 246, and an optional ejector 245. The ejector 245 may be located on the steam conduit 230, and the system recycling conduit 244 may fluidly connect the product conduit 240 to the ejector 245 located on the steam conduit 230. The vent conduit 246 may fluidly connect the product conduit 240 to an individual module exhaust or to a common system exhaust conduit which is fluidly connected to the vent conduits 246 of all modules. The ejector 245 may operate to pull a portion of the hydrogen product stream from the product conduit 240 through the system recycling conduit 244 and into the steam conduit 230 to recycle a portion of the hydrogen product stream back into the modules 200, while a remaining portion of the hydrogen product stream is provided to the hydrogen processor 40. In some embodiments, the ejector 245 may be replaced with a system recycle blower.

The system 300 may also include various flow control elements to control fluid flow to and/or from the modules 200. For example, the system 300 may include a primary steam valve 232 located on the steam conduit 230 and configured to control steam flow from the steam source 30 into through the steam conduit 230, and optional module shutoff valves 234 located between the steam conduit 230 and the respective modules 200 and configured to control the steam flow from the steam conduit 230 into the respective modules 200. The system 300 may also include a product valve 242 located on the product conduit 240 and configured to control hydrogen product flow from the product conduit 240 into the hydrogen processor 40. The system 300 may also include an optional recycling valve 249 located on the optional system recycling conduit 244 and configured to control a flow of the portion of the hydrogen product stream through the system recycling conduit 244. The system 300 may also include a hydrogen valve 252 located on the hydrogen conduit 250 and configured to control hydrogen flow from the hydrogen storage vessel 50 into the hydrogen conduit 250. The hydrogen valve 252 may be opened during system startup and shutdown modes to provide hydrogen from the hydrogen storage vessel 50 to the modules 200, and closed during a steady-state operating mode of the system 300 during which the system 300 generates the hydrogen product. The system 300 may also include a vent valve 248 located on the vent conduit 246 and configured to control hydrogen product flow through the vent conduit 246. For example, the vent valve 248 may be opened during system shutdown to vent the product conduit 240 and depressurize the system 300. In some embodiments, one or more of the valves may comprise gas solenoid valves or other suitable valves.

The system controller 225 may include a central processing unit and a memory. The system controller 225 may be wired or wirelessly connected to various elements of the system 300, and may be configured to control the same. The system controller may communicate and/or receive signals from sensors located on various components of the system 300 or from other controllers located in different modules, such as modules 200. Sensors may measure the temperature of stack components, voltage or current measurements, pressure in various conduits, the state of various valves, and the status of various modules (such as the operational status of the hydrogen processor 40, etc.). In addition, the system controller 225 may be configured to control the various valves and the operation of the modules 200. In one embodiment, the system controller 225 may be located in a power module which includes a housing separate from the housings of the electrolyzer modules 200. The power module may also include an AC/DC rectifier configured to convert alternating current (AC) power from a power source (e.g., power grid) to direct current (DC) power provided to the electrolyzer modules 200. The remaining components of the system 300 may be located either in a gas distribution module which includes a housing separate from the housings of the electrolyzer modules 200 and the power module, and/or outside the module housings of the system 300. For example, the steam source 30 and/or the hydrogen processor 40 may be located in the gas distribution module or separate from the module housings of the system 300. Likewise, the steam conduit 230 may extend from the gas distribution module to the electrolyzer modules 200 in or over a common base supporting the gas distribution module and the electrolyzer modules 200.

FIG. 3 is a schematic view of an electrolyzer module 200 that may be included in the electrolyzer system 300 of FIG. 2, according to various embodiments of the present disclosure. Referring to FIGS. 1A, 1B, 2 and 3, each module 200 may include an electrolyzer cell stack 100 including multiple electrolyzer cells, such as solid oxide electrolyzer cells (SOECs), as described with respect to FIGS. 1A and 1B. The stack 100 may be located in an electrolyzer cell column including plural stacks. Alternatively, the column may contain only a single stack 100. The module 200 may also include a steam recuperator heat exchanger 108, one or multiple steam heaters 110, an air recuperator heat exchanger 112, and one or multiple air heaters 114. The module 200 may also include an optional product cooler/air preheater heat exchanger 116, and an optional stack heater (not shown for clarity).

The module 200 may include a hotbox 202 to house various components, such as the stack 100, the steam recuperator 108, the steam heater 110, the air recuperator 112, and/or the air heater 114. In some embodiments, the hotbox 202 may include multiple stacks 100 and/or columns of stacks. The module 200 may also include a cabinet 204 configured to house the hotbox 202 and other module 200 components located outside of the hotbox 202. Optionally, the module 200 may also include a controller 125, such as a central processing unit, which is configured to control the operation of the module 200. For example, the controller 125 may be wired or wirelessly connected to various elements of the module 200 to control the same. Alternatively, the controller 125 may be located outside the housing of the electrolyzer module 200 (e.g., in the power module of the system 300). The product cooler 116 can be located inside the hotbox 202, or it can be located outside of the hotbox 202.

During operation, the stack 100 may be provided with steam from the steam source 30 and may be provided with electric power (e.g., DC current or voltage) from an external power source, such as a power grid. In particular, the steam may be provided to the fuel electrodes 7 of the electrolyzer cells 1 of the stack 100, and the power source may apply a voltage between the fuel electrodes 7 and the air electrodes 3, in order to electrolyze water molecules at the fuel electrodes 7 to form hydrogen gas and oxygen ions. In SOECs 1, the oxygen ions are transported through the solid electrolyte 5 to the air electrodes 3. Air may optionally be provided to the air electrodes 3 of the stack 100, in order to sweep the oxygen from the air electrodes 3. The stack 100 may output a hydrogen stream (e.g., hydrogen product which may also contain residual steam) into a module product conduit 140, and an oxygen-rich exhaust stream (e.g., an oxygen exhaust stream), such as an oxygen-rich air stream (i.e., oxygen enriched air) into a module exhaust conduit 170.

The steam output from the steam source 30 may be provided to the multiple modules 200 via the steam conduit 230. The steam entering a module 200 from the steam conduit 230 may be provided to the steam recuperator 108 via a module steam conduit 130. The steam may include small amounts of dissolved air and/or oxygen. As such, the steam may be mixed with hydrogen gas, in order to maintain a reducing environment in the stack 100, and in particular, at the fuel electrodes 7. An optional shutoff valve 134 and an optional non-return valve 136 may be located on module steam conduit 130. The non-return valve 136 is configured to prevent the backflow of steam from the module steam conduit 130 into the steam conduit 230. However, in some embodiments, the non-return valve 136 may be omitted. For example, operation of the shutoff valve 134 may be sufficient to prevent steam backflow.

Hydrogen may be provided to the steam from the hydrogen storage vessel 50 and/or from a portion of the hydrogen product generated by the stack 100. The hydrogen addition rate may be set to provide an amount of hydrogen that exceeds an amount of hydrogen needed to react with an amount of oxygen dissolved in the steam. The hydrogen addition rate may either be fixed or set to a constant water to hydrogen ratio. However, if the steam is formed using water that is fully deaerated, the hydrogen addition may optionally be omitted.

In some embodiments, the hydrogen may be provided by the external hydrogen storage vessel 50 during system startup and shutdown. For example, during the system 300 startup and/or shutdown modes, hydrogen may be provided from the hydrogen storage vessel 50 to the steam conduit 230 via the hydrogen conduit 250. In contrast, during the steady-state operation mode, a portion of the hydrogen product (i.e., hydrogen exhaust stream) may be diverted from the product conduit 240 to the steam conduit 230 via the recycling conduit 244, and the hydrogen flow from the hydrogen storage vessel 50 may be stopped by closing the shutoff valve 252 on the hydrogen conduit 250.

In some embodiments, the module 200 may include a recycle blower 122 configured to selectively divert a portion of the generated hydrogen product to the steam in the module steam conduit 130. For example, the recycle blower 122 may be located on a module recycling conduit 124 which fluidly connects a module product conduit 140 to the module steam conduit 130. Alternatively, a hydrogen pump may be used instead of the recycle blower 122. In some embodiments, the portion of the generated hydrogen product may be diverted from the module product conduit 140 to the module recycling conduit 124 by a splitter and/or valve.

The steam recuperator 108 may be a heat exchanger configured to recover heat from the hydrogen stream output from the stack 100 into the module product conduit 140. The steam may be heated to at least 600° C., such as 620° C. to 780° C. (depending in part on the stack 100 operating temperature) in the steam recuperator 108.

The steam output from the steam recuperator 108 may be provided to the steam heater 110 which is located downstream from the steam recuperator 108 on the module steam conduit 130, as shown in FIG. 3. The steam heater 110 may include a heating element, such as a resistive or inductive heating element. The steam heater 110 may be configured to heat the steam to a temperature above the operating temperature of the stack 100. For example, depending on the health of the stack 100, the water utilization rate of the stack 100, and the air flow rate to the stack 100, the steam heater 110 may heat the steam to a temperature ranging from about 700° C. to about 850° C., such as 720° C. to 780° C. Accordingly, the stack 100 may be provided with steam or a steam-hydrogen mixture at a temperature that allows for efficient hydrogen generation. Heat may also be transported directly from the steam heater to the stack by radiation (i.e., by radiant heat transfer). If the stack operating current is sufficiently high to maintain the stack at a desired steady-state operating temperature, then the steam heater and/or the air heater may be turned off. In some embodiments, the steam heater 110 may include multiple steam heater zones with independent power levels (divided vertically, circumferentially, or both), in order to enhance thermal uniformity.

An air blower 118 may provide an air inlet stream to the air recuperator 112 via a module air inlet conduit 120. The module air inlet conduit 120 fluidly connects the air blower 118 to an air inlet of the stack 100 through the product cooler 116. The oxygen exhaust output from the stack 100 may be provided via the module exhaust conduit 170 to the air recuperator 112. The air recuperator 112 may be configured to heat the air inlet stream using heat extracted from the oxygen exhaust.

Air output from the air recuperator 112 may be provided to the air heater 114 via a continuation of the air inlet conduit 120 inside the hotbox. The air heater 114 may include a resistive or inductive heating element configured to heat the air to a temperature exceeding the operating temperature of the stack 100. For example, depending on the health of the stack 100, the water utilization rate of the stack 100, and the air flow rate to the stack 100, the air heater 114 may heat the air to a temperature ranging from about 700° C. to about 850° C., such as 720° C. to 880° C. Accordingly, the stack 100 may be provided with air at a temperature that allows for efficient hydrogen generation. Heat may also be transported directly from the air heater to the stack by radiation. In some embodiments, the air heater 114 may include multiple air heater zones with independent power levels (divided vertically or circumferentially or both), in order to enhance thermal uniformity. Air from the air heater 114 is provided to the air electrodes 3 of the stack 100.

Oxygen exhaust (e.g., oxygen enriched air) output from the air recuperator 112 may be provided to the exhaust conduit 270 via the module exhaust conduit 170 and an exhaust duct 206 of the cabinet 204. A fan 208 or multiple fans 208 may optionally be located in the exhaust duct 206 to improve oxygen exhaust flow through the exhaust conduit 270. The exhaust conduit 270 may be configured to receive oxygen exhaust output from multiple modules 200. In some embodiments, the exhaust conduit 270 may provide the exhaust to a chimney or may provide the air exhaust to the atmosphere. In other embodiments, the oxygen exhaust (e.g., oxygen enriched air) may be provided from the exhaust conduit 270 for purification and/or use. In some embodiments, the cabinet 204 may contain a cabinet ventilation fan that comprises the fan 208 or another fan in addition to the fan 208. The cabinet ventilation stream may be merged with the oxygen exhaust stream to lower the temperature and oxygen concentration of the oxygen exhaust stream before exhausting it to the atmosphere.

In some embodiments, the module 200 may include an optional product cooler/air preheater heat exchanger 116, which may be located outside (e.g., on top of) of the hotbox 202 or inside of the hotbox 202. The product cooler 116 may be fluidly connected to the hydrogen product conduit 240 by the module product conduit 140. The product cooler 116 may be configured to preheat the air inlet stream provided to the hotbox 202 via the module air inlet conduit 120 using heat from the hydrogen product in the module product conduit 140, and to cool a hydrogen product output from the stack 100 using the air inlet stream provided from the air blower 118.

The hydrogen product stream is output from the steam recuperator 108 and the optional product cooler 116 via the module product conduit 140 and the product conduit 240 at a temperature of 100° C. to 200° C. The hydrogen product stream may be compressed and/or purified in the hydrogen processor 40, which may include a hydrogen pump (e.g., proton exchange membrane electrochemical pump) that operates at a temperature of from about 40° C. to about 120° C., in order to remove from about 70% to about 90% of the hydrogen from the hydrogen product stream. A remaining a water rich stream comprises a unpumped effluent from the hydrogen pump.

In various embodiments, the hydrogen processor 40 may include at least one electrochemical hydrogen pump, liquid ring compressor, diaphragm compressor or combination thereof. For example, the hydrogen processor may include a series of electrochemical hydrogen pumps, which may be located in series and/or in parallel with respect to a flow direction of the hydrogen stream, in order to compress the hydrogen stream. Electrochemical compression may be more electrically efficient than traditional compression. Traditional compression may occur in multiple stages, with interstage cooling and water knockout. The final product from compression may still contain traces of water. As such, the hydrogen processor 40 may include a dewatering device, such as a temperature swing adsorption reactor or a pressure swing adsorption reactor, to remove this residual water, if necessary.

Internal Venting

In the electrolyzer system 300, if one electrolyzer module 200 has a fault and is required to be vented, then all of the electrolyzer modules 200 connected to the same system vent conduit 246 (e.g., vent header) are also required to stop operation because the system vent valve 248 is opened to vent the hydrogen product stream from the faulted module 200. For example, eight or more modules may be connected to the same system vent header 246. As such, all eight electrolyzer modules 200 would stop operation and enter a vent state in which their product conduits 140 are vented.

FIG. 4A illustrates an electrolyzer system 400 that is configured to independently vent a faulted electrolyzer module 200 without stopping the operation and venting the other electrolyzer modules 200 of the system 400. FIG. 4B is a schematic view of an electrolyzer module 200 that may be included in the electrolyzer system 400 of FIG. 4A, according to various embodiments of the present disclosure. The system 400 is similar to system 300. Thus, only the differences between the systems 300 and 400 are described below.

Referring to FIGS. 4A and 4B, each electrolyzer module 200 in system 400 includes a module vent conduit 146 which is fluidly connected to the module product conduit 140 inside the module 200 cabinet 204, instead of or in addition to the system vent conduit 246 fluidly connected to the system product conduit (e.g., system product header) 240 of the system 300. Thus, each faulted electrolyzer module 200 in the system 400 may be stopped and vented through the module vent conduit 146 while the remaining non-faulted electrolyzer modules 200 in the system 400 continue to operate to generate the hydrogen product stream without being vented.

The system 400 may also optionally include an inert gas storage vessel 60 and a system inert gas conduit (e.g., inert gas header) 260 which fluidly connects each module 200 to the inert gas storage vessel 60. The inert gas storage vessel 60 may comprise a pressurized nitrogen gas storage vessel (e.g., a nitrogen tank) which stores pressurized nitrogen gas at an elevated pressure (e.g., 10 to 60 psig). A gas safety valve 266 may be disposed on the inert gas conduit 260. Furthermore, in the system 400, the system hydrogen conduit (e.g., hydrogen header) 250 may optionally extend into each electrolyzer module 200 cabinet 204, instead of being fluidly connected to the steam conduit 230 on a system level outside the electrolyzer module 200 cabinets 204.

FIG. 5 is a perspective view showing components inside of the cabinet 204 of the electrolyzer module 200 of FIG. 4B, according to various embodiments of the present disclosure. Referring to FIGS. 4A, 4B and 5, the module 200 may include a module product conduit 140, a recycling conduit 124, a module vent conduit 146, a module exhaust conduit 170, and an exhaust duct 206. The module product conduit 140 may be configured to fluidly connect an outlet of the hotbox 202 and/or the air preheater 116 if included, to the system product conduit 240. The recycling conduit 124 may fluidly connect the module product conduit 140 to a mixer 106. The vent conduit 146 may fluidly connect the module product conduit 140 to the exhaust duct 206. The exhaust duct 206 may be disposed at the rear of the cabinet 204 and may be fluidly connected to the system exhaust conduit 270. At least one exhaust fan 208 may be located in the exhaust duct 206. The module exhaust conduit 170 may fluidly connect the outlet of the air recuperator 112 to the exhaust duct 206.

The module 200 may also include a module steam conduit 130 configured to provide steam from the system steam conduit 230 to the mixer 106, a module hydrogen conduit 150 configured to provide hydrogen from the system hydrogen conduit 250 to the mixer 106, and a first purge conduit 160 configured to provide an inert purge gas (e.g., nitrogen) received from the system inert gas conduit 260 to the module hydrogen conduit 150 (or to the mixer 106 in an alternative embodiment). The module may also include a secondary air conduit 180 configured to provide air to the fuel side (e.g., fuel electrodes 7 of the electrolyzer cells 1) of the stack 100 in the hotbox 202. A secondary air blower 184 is located on the secondary air conduit 180. The secondary air conduit 180 may be fluidly connected to the module hydrogen conduit 150 or to the mixer 106.

The module 200 may also include a module vent conduit 146 which fluidly connects the module product conduit 140 to the exhaust duct 206, and at least one vent valve 148 disposed on the module vent conduit 146. At least one hydrogen valve 152 may be disposed on the module hydrogen conduit 150, at least one first purge valve 162 may be disposed on the first purge conduit 160, and at least one shutoff valve 182 disposed on the secondary air conduit 180. In some embodiments, the module 200 may optionally include at least one steam valve 132 disposed on the module steam conduit 130.

In various embodiments, the valves 132, 148, 152, 162, 182 may be any suitable type of shutoff valve, such as an electric or pneumatic gas safety valve, for example gas solenoid valves. The valves 132, 152, 162, 182 may be normally open/fail closed valves (e.g., open during normal operations and closed when de-energized). The vent valves 148 may be normally closed/fail open valves (e.g., closed during normal operations and opened when de-energized). In some embodiments, the vent conduit 146 may be connected to the product conduit 140 by vent mixer (e.g., a T-junction) 212 and may be connected to the exhaust duct 206 by a plate and gasket interface 214, for example.

In some embodiments, the module 200 may include pairs of one or more of the valves 132, 148, 152, 162, 182, in order to increase system reliability and/or safety. For example, as shown in FIGS. 4B and 5, the module 200 may include two vent valves 148 that may be disposed on the module vent conduit 146. The module vent conduit 146 may be attached to the module cabinet 204 by a bracket 210, as shown in FIG. 5. In some embodiments, the module 200 may include two or more exhaust conduits 170 to connect the hotbox 202 to the exhaust duct 206. However, for simplicity of explanation, the valves and exhaust conduits will be described below as single valves and a single exhaust conduit.

As discussed in detail above, when the module 200 is operating in a steady-state mode (e.g., normal hydrogen production operation), the hydrogen product stream may be output from each module 200 to the hydrogen processor 40 via the module product conduit 140 and the system product conduit (e.g., header) 240. In some embodiments, the recycle blower 122 may be operated to divert a portion of the hydrogen product stream to the mixer 106 via the recycling conduit 124. As such, the hydrogen valve 152 may be opened during system 400 startup and shutdown modes to provide hydrogen from the hydrogen storage vessel 50 to the fuel electrodes 7 of the cells 1 in the stack 100, and closed during the steady-state mode so that no external hydrogen is provided to the module 200 from the hydrogen storage vessel 50.

In addition, the vent valve 148 may be closed and the air blower 118 may be operated to provide air to the stack 100 during the steady-state mode. Oxygen exhaust stream may be output from the module 200 to the system exhaust conduit (e.g., header) 270 via the module exhaust conduit 170 and the exhaust duct 206. The exhaust fan 208 may be operated to pull the oxygen exhaust stream (i.e., the oxygen-enriched air stream) from the module exhaust conduit 170 and cabinet air from the cabinet 204 through the exhaust duct 206 and to provide the mixture of the oxygen exhaust stream and the cabinet air into the system exhaust conduit 270.

Accordingly, during steady-state mode, the exhaust fan 208 may be operated, the steam valve 132 and the system product valve 242 may be open, and the remainder of the valves may be closed. In particular, the vent valve 148 may be closed to prevent the hydrogen product from flowing into the exhaust duct 206.

If a problem is detected, such as if one or more of the modules 200 experiences a fault, the system 400 may shut down the faulted module(s) 200, while the remaining non-faulted modules 200 continue operating. In other words, the system 400 may signal one or more of the modules 200 to enter a non-steady-state mode, such as a shutdown mode or a startup/restart mode.

During the shutdown mode, power flow to the stack 100 may optionally be stopped, and the faulted module 200 may be disconnected from the system steam conduit 230 and/or the system product conduit 240. In other words, the steam valve 132 may be closed to stop the flow of steam into the faulted module 200 from the system steam conduit 230. In addition, the system product valve 242 may be closed at the faulted module 200 to stop hydrogen product flow through the module product conduit 140 to the system product conduit 240. In addition, the vent valve 148 may be opened to allow the hydrogen product stream to enter the exhaust duct 206 and be provided to the system exhaust conduit (e.g., header) 270. The hydrogen product stream is mixed with the oxygen exhaust stream and the cabinet air in the exhaust duct 206 prior to being provided to the system exhaust conduit 270. The air blower 118 may be operated to circulate air through the components located in the hotbox 202.

The module 200 may then be purged by flushing the stack 100 with a purge gas. In one embodiment, the first valves 162 may be opened to provide nitrogen gas (N₂) to the fuel electrodes 7 of the electrolyzer cells 1 in the stack 100 through the mixer 106. The module hydrogen valve 152 may also optionally be opened to allow hydrogen to flow from the hydrogen storage vessel 50 and mix with the purge gas steam. As such, a purge gas stream comprising nitrogen and hydrogen may flow into the hotbox 202. The purge gas may flow through the steam recuperator 108, the steam heater 110, and over the fuel electrodes 7 of the electrolyzer cells 1 in the stack 100 to purge the stack 100. Because the purge gas includes an inert gas (e.g., N₂) and optionally a reducing gas (e.g., H₂), the purge gas may prevent and/or reduce oxidation of the nickel to nickel oxide in the cermet fuel electrodes 7 of the electrolyzer cells 1 as the stack 100 cools. In particular, the purge gas may maintain a reducing environment in the fuel side (e.g., at the fuel electrodes) of the stack 100 by preventing the ingress of oxygen to the stack 100. The vent valve 148 may be open and the system product valve 242 may be closed during the purging process, such that purge gas output from the hotbox 202 flows through the module product conduit 140 and then into the module vent conduit 146 and the exhaust duct 206.

In some embodiments, the hydrogen storage vessel 50 and the inert gas storage vessel 60 may provide pressurized hydrogen and nitrogen to the module 200. For example, the hydrogen stored in the hydrogen storage vessel 50 may have a pressure ranging from about 10 psig to about 30 psig, such as from about 12 psig to about 20 psig, while the nitrogen stored in the hydrogen storage vessel 50 may have a pressure ranging from about 10 psig to about 60 psig, such as from about 15 psig to about 45 psig. As such, the valves 152, 162 may be opened, such that a pressurized purge stream comprising nitrogen and optionally hydrogen may flow into the faulted module 200.

The module 200 may optionally include a proportional flow control valve 154 disposed on the hydrogen conduit 150. The proportional flow control valve 154 may be configured to control a mass flow rate of hydrogen into the mixer 106. As such, the proportional flow control valve 154 may be configured to control an amount of hydrogen that is included in the first purge stream. For example, the proportional flow control valve 154 may be configured to reduce the hydrogen mass flow rate, such that the first purge stream has a relatively low hydrogen content and a relatively high nitrogen content. Reducing the relative amount of hydrogen in the first purge stream may beneficially reduce the risk of hydrogen oxidation, while still maintaining a reducing environment in the stack 100. Alternatively, the hydrogen valve(s) 152, 154 may be closed during the purging step so that only nitrogen gas is used to purge the fuel side of the stack 100 in the faulted module 200.

In various embodiments, the faulted module 200 may be restarted without disrupting the operation of the remaining modules 200. In particular, electric power, steam and air may be provided to the stack 100 by operating the air blower 118 and opening the steam valve 132 and the vent valve 148. The heaters may also be turned on to heat the stack 100. The hydrogen and flow control valves 152, 154 may also be opened to provide hydrogen to the incoming steam. The remaining valves may be closed. As such, the steam and/or hydrogen output from the stack 100 may be vented into the system exhaust conduit 270 via the vent conduit 146, until the stack 100 reaches operating temperature and begins producing the hydrogen product. As this point, the vent valve 148 may be closed and the system product valve 242 may be opened to provide the hydrogen product stream to the hydrogen processor 40. The recycle blower 122 may also be operated to recycle a portion of the hydrogen product stream to the mixer 106, and the hydrogen valves 152 and the flow control valve 154 may be closed.

Over time, the performance of the cermet fuel electrodes 7 of the cells 1 of the stack 100 may be reduced. In one embodiment, stack performance may be improved by oxidizing and reducing the fuel electrodes 7. In this embodiment, after the flow of steam has been stopped and the stack 100 remains at an elevated temperature, the secondary air blower 184 may be operated to provide air via the secondary air conduit 180 to the fuel electrodes 7 of the cells 1 in stack 100 to oxidize the nickel to nickel oxide in the cermet fuel electrodes 7. For example, oxygen may be provided for 10 to 120 minutes, such as 30 to 90 minutes. After oxidizing the fuel electrodes 7, the secondary air blower 184 is stopped, and the valves 182 are closed. The hydrogen valves 152, 154 are opened and hydrogen is provided from the hydrogen storage vessel 50 to the fuel electrodes 7 via the module hydrogen conduit 150 to reduce the nickel oxide to nickel metal in the cermet fuel electrodes 7. After the reduction step, the fuel electrodes 7 include a nickel metal phase and a ceramic oxide phase (e.g., doped ceria or stabilized zirconia). Optionally, steam may be mixed with the hydrogen during the reduction step by opening the steam valve 132 on the module steam conduit 130.

Thus, in one embodiment, a method of operating a solid oxide electrolyzer cell stack 100 comprises providing steam to nickel cermet fuel electrodes 7 of solid oxide electrolyzer cells 1 of the solid oxide electrolyzer cell stack 100 and applying electric power to the stack 100 to electrolyze the steam to generate a hydrogen product stream; stopping providing the steam to the fuel electrodes 7 of the stack 100; providing air to the fuel electrodes 7 to oxidize the nickel to nickel oxide; and providing hydrogen to the fuel electrodes 7 to reduce the nickel oxide to nickel.

In one embodiment, the steam is again provided to the fuel electrodes 7 after providing the hydrogen to the fuel electrodes 7. In one embodiment, the air and the hydrogen are provided to the fuel electrodes 7 at a temperature above 600° C., such as 600° C. to 1,100° C.

In various embodiments shown in FIGS. 4A, 4B and 5, a method of operating an electrolyzer system 400 includes providing steam and air to a stack 100 of electrolyzer cells 1 located in a first hotbox 202 of a first electrolyzer module 200, operating the stack 100 in a steady-state mode to generate a hydrogen product stream and an oxygen exhaust stream, to provide the hydrogen product stream from the first hotbox to a product header 240 and to provide the oxygen exhaust stream from the first hotbox 202 to an exhaust duct 206, and operating the stack 100 in a fault mode by providing both the hydrogen product stream and the oxygen exhaust stream to the exhaust duct 206.

In one embodiment, the first electrolyzer module 200 includes a first electrolyzer module cabinet 204 housing the first hotbox 202 and the exhaust duct 206. In one embodiment, the method also includes mixing the hydrogen product stream and the oxygen exhaust stream with cabinet 204 air during the fault mode; and venting the cabinet air, the hydrogen product stream and the oxygen exhaust stream from the first electrolyzer module cabinet 204 via the exhaust duct 206 during the fault mode.

In one embodiment, the hydrogen product stream is provided from the first hotbox 202 to the product header 240 via a product conduit 140 located in the first cabinet 204 during the steady-state operating mode; a vent conduit 146 fluidly connects the product conduit 140 to the exhaust duct 206; a vent valve 148 disposed on the vent conduit 146 is closed during the steady-state operating mode such that the hydrogen product stream is not provided from the product conduit 140 to the exhaust duct 206 through the vent conduit 146 during the steady-state operating mode; and the vent valve 148 is opened during the fault mode to provide the hydrogen product stream from the product conduit 140 to the exhaust duct 206 through the vent conduit 146 during the fault mode.

In one embodiment, the system 400 also includes additional electrolyzer modules 200 comprising additional hotboxes 202 containing respective additional stacks 100 of electrolyzer cells 1. The method also includes operating the additional electrolyzer modules 200 in the steady-state operating mode to provide the hydrogen product stream from the additional hotboxes to the product header 240 while the first electrolyzer module operates 200 in the steady-state mode; and continuing to operate the additional electrolyzer modules 200 in the steady-state operating mode to provide the hydrogen product stream from the additional hotboxes 202 to the product header 240 while the first electrolyzer module 200 operates in the fault mode and provides the hydrogen product stream to the exhaust duct 206 instead of the product header 240.

In one embodiment, the method also includes providing the steam to the first electrolyzer module 200 and to the additional electrolyzer modules 200 through a common steam header 230 while the first electrolyzer module 200 and the additional electrolyzer modules 230 are operating in the steady-state operating mode; stopping providing the steam to the first electrolyzer module 200 while the first electrolyzer module operates in the fault mode, while continuing to provide the steam to the additional electrolyzer modules 200 through the common steam header 230 while the additional electrolyzer modules continue to operate in the steady-state operating mode; and providing an inert purge gas (e.g., nitrogen from the nitrogen storage vessel 60) to fuel electrodes 7 of the electrolyzer cells 1 in the stack 100 located in the first hotbox 202 when the first electrolyzer module 200 switches from operating in the steady-state operating mode to operating in the fault mode.

In various embodiments, the system 400 may include other components such as additional valves, flow regulators, temperature sensors, pressure sensors, temperature sensors, filters, or the like. The modules 200 may also include one or more one-way valves 156, 166 (e.g., non-return valves) disposed on the hydrogen conduit 150 and/or the first purge conduit 160 that are configured to prevent the backflow of steam into conduits 150, 160 and/or 180.

The system 400 may include the system controller 225 configured to control the module controllers 125 and/or other components of the system 400. If the module controller 125 receives a shutdown signal from the system controller 225 or receives a module-generated shutdown signal, the module controller 125 may be configured to control the module valves, in order to shutdown, purge, condition, and/or restart the module 200, as described above.

Accordingly, various embodiments of the present disclosure provide electrolyzer systems that include electrolyzer modules that can be stopped, purged, conditioned, and/or restarted, while being connected to a common product header with other electrolyzer modules which remain operating in a steady-state mode, which allows for remaining modules to remain at full hydrogen production. In particular, the modules may include module vent conduits and valves that allow for a hydrogen product stream and/or purge gasses to be exhausted through a module exhaust duct. The gasses may be cooled and diluted with air (e.g., cabinet air and/or stack air exhaust stream) in the exhaust duct before being exhausted to the atmosphere, thereby improving system safety.

Various embodiments of the present disclosure provide a benefit to the climate by reducing greenhouse gas emissions and/or generating carbon-free fuel.

The preceding description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.