ELECTROLYZER SYSTEM INCLUDING STEAM FLOW RESTRICTORS AND METHODS OF OPERATING SAME

Description

FIELD

The present invention is directed to solid oxide electrolyzer cell (SOEC) systems including steam flow restrictors 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 system includes first hotbox containing a stack of electrolyzer cells configured to electrolyze steam into a hydrogen product, a first steam conduit configured to provide the steam to the first hotbox, and a first flow restrictor containing at least one aperture located on the first steam conduit. The first flow restrictor is configured to generate a first pressure drop in the steam flowing through the first steam conduit.

In various embodiments, a method of operating an electrolyzer system comprises providing steam to a stack of electrolyzer cells located in a first hotbox through a first steam conduit containing at least a first flow restrictor comprising at least one aperture, wherein the first flow restrictor is configured to generate a first pressure drop in the steam flowing through the first steam conduit; and electrolyzing the steam into a hydrogen product in the stack of electrolyzer cells.

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. 3A is a schematic view of an electrolyzer module that may be included in the electrolyzer system of FIG. 2, and FIG. 3B is a schematic view of a steam flow restrictor that may be included in the system of FIG. 2.

FIG. 4 is a schematic view of an alternative electrolyzer system, according to various embodiments of the present disclosure.

FIGS. 5A and 5B are schematic views of alternative electrolyzer systems, according to various embodiments of the present disclosure.

FIG. 6 is a schematic view of an alternative electrolyzer system, 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.

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™ 22 APU alloy which contains 20 to 24 wt. % Cr, less than 1 wt. % Mn, Ti and La, and balance Fe, or ZMG™ 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 the steam conduit 230, and 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 a 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 be relatively simple, fast acting on/off valves (e.g., shutoff valves, gas safety valves, etc.). The valves may comprise electrically actuated valves, such as gas solenoid valves, pneumatically actuated valves, and/or pressure actuated valves (e.g., normally closed gas safety valves which open in case of an overpressure in the respective conduit).

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. For example, 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. 3A 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 3A, each module 200 may include one or more electrolyzer cell stacks 100 including multiple electrolyzer cells, such as solid oxide electrolyzer cells (SOECs), as described with respect to FIGS. 1A and 1B. The stacks 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 include multiple SOEC columns. 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 120, 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 126.

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 132. 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.

Hydrogen may be provided to the steam conduit 230 from the hydrogen storage vessel 50 via the hydrogen conduit 250 and/or from a portion of the hydrogen product generated by the stack 100 via the recycling conduit 244. 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 module steam conduit 132. For example, the recycle blower 122 may be located on a module recycling conduit 124 which fluidly connects a module product conduit 120 to the module steam conduit 132. Alternatively, a 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 120 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 120. 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 132, as shown in FIG. 3A. 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 119. The module air inlet conduit 119 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 126 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 via the air inlet conduit 119 may be provided to the air heater 114. 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 output from the air recuperator 112 may be provided to the exhaust conduit 270 via the module exhaust conduit 126 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 module 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 120. The product cooler 116 may be configured to preheat the air inlet stream provided to the hotbox 202 via the module air inlet conduit 119 using heat from the hydrogen product in the module product conduit 120, 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 120 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.

Electrolyzer systems may have different steam mass flow requirements during system startup mode, steady-state operating mode, and shutdown mode. Prior art electrolyzer systems utilize relatively expensive individual steam flow control valves (e.g., valves which control an amount of steam flowing through them rather than on/off valves) and/or mass flow controllers, in order to provide desired and/or different steam flow rates to individual modules 200 and hotboxes 202 from a common steam source. Such control elements also utilize steam flow meters which measure the steam flow rate and provide the steam flow rate to a controller which controls these control elements based on the received steam flow rate from the steam flow meters.

However, the use of steam control valves, mass flow controllers and/or flow meters may increase system costs. Steam flow meters also need periodic recalibration and re-zeroing over time. Steam control valves and mass flow controllers also need periodic inspection to insure proper operation, which increases maintenance costs.

Furthermore, a steam flow meter can generally accurately measure steam flow rates down to specific percent of its maximum capacity. In other words, steam flow meters may not provide accurate measurements at low flow rates. In addition, in order to provide a fine mass flow control utilized during steady-state operation, valve travel, actuator speed, and controller settings are generally set in a way that reduces valve ramp rates (e.g., valve response time). In other words, proportional valves that provide fine flow control generally have slow opening and closing speeds. A slow valve response time may result in an undesirable delay in reaching steady-state operating mode hydrogen production and may lead to fuel starvation due to an insufficient supply of steam during startup. In contrast, a fast valve response speed reduces module recovery time and decreases the risk of fuel starvation. However, valves that have a fast response speed generally lack fine flow control.

Accordingly, various embodiment provide electrolyzer systems that utilize steam flow restrictors instead of or in addition to one or more steam valves, in order to provide consistent and reliable steam flow, while also reducing system costs.

FIG. 3B illustrates a flow restrictor 140 that may be included in electrolyzer module 200 of FIG. 3A, according to various embodiments of the present disclosure. Referring to FIGS. 2, 3A, and 3B, each module 200 may include an optional shutoff valve 134, an optional non-return valve 136, and a flow restrictor 140 located on the module steam conduit 132. The module steam conduit 132 may receive steam from the system steam conduit 230 and provide the steam to the hotbox 202 of the electrolyzer module 200.

The shutoff valve 134 may be a normally closed gas safety valve that is opened during operation of the module 200. The shutoff valve 134 may be an on/off valve which has a rapid response speed. For example, the shutoff valve 134 may be an electrically or pneumatically actuated valve, such as a solenoid valve having an opening/closing response time of less than 1 second, such as less than 0.1 seconds, such as 0.03 to 0.04 seconds. As such, the shutoff valve 134 may provide a significantly faster response speed than a proportional steam mass flow control valve. In embodiments that include pneumatic shutoff valves 134, the system 300 may include a compressed air source, as such as an air compressor or tank, which may be connected to the shutoff valve 134 and other pneumatic shutoff valves, such as the primary steam valve 232 and/or other valves described above.

The non-return valve 136 may be configured to prevent the backflow of steam from the module steam conduit 132 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.

Referring to FIG. 3B, the flow restrictors 140 may each include a restrictor plate 142 having an orifice 144 configured to restrict steam flow. In other embodiments, the restrictor plate 142 may include multiple orifices 144 configured to restrict steam flow. As such, the flow restrictors 140 may be configured to create a first amount of pressure drop in steam passing through the at least one orifice 144. In other words, the flow restrictors 140 may be configured to provide a consistent (e.g., constant) steam flow rate to each of the hotboxes 202 at a given constant incoming steam pressure.

During system startup, the shutoff valve 134 of each module 200 may be opened. After the shutoff valve 134 is opened, steam flows through the module steam conduit 132 and the flow restrictor 140 and is provided to the hotbox 202 of each module 200 at a corresponding first steam flow rate. The steam temperature may be at least 110° C., such as 110 to 200° C., for example 130 to 150° C.

The first steam flow rate may be sufficient to rapidly heat up each module 200 and may also be sufficient for steady-state operation of the module 200. In particular, the first steam flow rate may be sufficient prevent electrolyzer cell 1 steam starvation, and may also provide a high steam utilization rate by preventing an excessive steam mass flow to the stacks 100.

During the startup mode, the steam may be heated in the hotbox 202 using the steam recuperator 108 and the steam heater 110 and then provided to the stack 100. The heated steam and hydrogen from the hydrogen storage vessel 50 exiting the stack 100 in the start-up mode may be partially recycled via the system recycling conduit 244 and/or the module recycling conduit 124 until the stack 100 reaches steady-state operating temperature, at which point, at least some of the hydrogen product generated by the stack 100 may be exported to the hydrogen processor 40 via the module product conduit 120. Each module outputs at least some net product, either through the vent valve 248 or through the product valve 242. Potential module recycle conduit 124 and recycle blower 122 overheating may be addressed by increasing the air inlet stream flow rate to the product cooler 116 to decrease the temperature of the recycle stream flowing through the recycle blower 122. In case of a steam delivery disruption during system startup mode, the shutoff valve 134 may be closed to stop steam flow to the hotbox 202, and the system 300 may enter a standby state. The system 300 can be safely cooled down by closing the shutoff valve 134, with the cool-down rate controlled by the air inlet stream flow to the modules 200.

Using a flow restrictor 140 that provides a consistent steam flow rate in conjunction with a rapidly actuated shutoff valve 134 significantly improves ramp rates from open circuit voltage (OCV) to full hydrogen production in the steady-state operating mode, compared with using a slowly actuated proportional valve and/or mass flow controller to control a steam flow rate. The flow restrictor 140 and shutoff valve 134 configuration also reduces recovery time and minimizes the risk of fuel starvation due to insufficient steam supply during module 200 recovery.

In general, the hydrogen storage vessel 50 provides hydrogen to the stack 100 in an amount that is sufficient to remove oxygen from the steam generated by the steam source 30. In various embodiments, this may be a relatively small amount of hydrogen. The hydrogen delivery rate can be controlled to match the system requirements.

The needed fuel and health of the stacks 100 in the selected module 200 may be assessed (i.e., tested) by supplying a current to the stacks 100 to generate hydrogen and then measuring a voltage of the stacks 100. In particular, the testing process may include sensitivity analysis of the voltage of the stacks 100 to different fuel (i.e., steam) flow rates at a given current to determine sensitivity to the supplied fuel and health of the stacks 100 and to determine an optimum operating fuel (i.e., steam or water) utilization of the module 200. The shutoff valve 134 of the selected module 200 may then be closed and the process may be repeated to sequentially reduce the fuel electrodes 7 in each remaining module 200 and assess each remaining module 200.

In various embodiments, once all modules have been assessed, the modules 200 may be simultaneously restarted. In particular, the shutoff valves 134 of all modules 200 of the system 300 may be opened to provide steam to the modules 200 to heat the modules to operating temperature. The flow restrictors 140 may ensure that each of the modules 200 is provided with steam at substantially the same steam flow rate. In particular, the steam flow rate to each of the hotboxes 202 may vary by about 5% or less, such as by about 3% or less, by about 2% or less, or by about 1% or less, such as 0 to 0.5%. In some embodiments, if one or more of the modules 200 is faulted (i.e., does not pass the test during the testing step), the faulted module 200 may be taken offline by closing the corresponding shutoff valve 134 and/or 234.

FIG. 4 illustrates an alternative electrolyzer system 400, according to an alternative embodiment of the present disclosure. The electrolyzer system 400 may be similar to the electrolyzer system 300. As such, only the differences therebetween will be discussed in detail.

Referring to FIGS. 2 and 4, the electrolyzer system may include steam manifolds 430 that control steam flow from the steam conduit 230 into each module 200. In particular, the steam manifold 430 of each module 200 may be configured to control steam flow from the steam conduit 230 to the hotbox 202 of the respective module 200. The steam manifold 430 may be located within the cabinet 204, as shown in FIG. 4. Alternatively, at least a portion of the steam manifolds 430 may be located outside of the cabinets 204 of the modules 200.

In various embodiments, the steam manifold 430 may include a first steam conduit 132a and a second steam conduit 132b, and may optionally include a third steam conduit 132c. The steam conduits 132a-132c may be fluidly connected to the hotbox 202 and steam conduit 230. The steam manifold 430 may also comprise a first shutoff valve 134a and a first flow restrictor 140a that are located on the first steam conduit 132a, a second shutoff valve 134b and a second flow restrictor 140b that located on the second steam conduit 132b, and may optionally include a third shutoff valve 134c and a third flow restrictor 140c that are located on the third steam conduit 132c.

The shutoff valves 134a-134c may be gas safety valves having a rapid response speed. For example, the shutoff valves 134a-134c may be electrically or pneumatically actuated solenoid valves having an opening/closing response time of less than 1 second, such as less than 0.1 seconds, such as 0.03 to 0.04 seconds. As such, the shutoff valves 134a-134c may provide a significantly faster response speed than a proportional flow control valve. In embodiments that include pneumatic shutoff valves 134a-134c, the system 400 may include a compressed air source 60, as such as an air compressor or tank, which may be connected to the shutoff valves 134a-134c and/or other pneumatic shutoff valves, such as the primary steam valve 232 and/or other valves described above.

The flow restrictors 140a-140c may be configured to provide different amounts of pressure drop, such that the flow restrictors 140a-140c each provide a different steam flow rate when provided with steam at a given pressure from the steam conduit 230. For example, the first flow restrictor 140a may provide a first steam flow rate, the second flow restrictor 140b may provide a second steam flow rate different from the first steam flow rate, and the third flow restrictor 140c may provide a third steam flow rate different from the first and second steam flow rates, at a given incoming steam pressure. For example, the second flow restrictor 140b may have a larger orifice 144 or a larger total orifice 144 area than the first flow restrictor 140a, in which case the second flow restrictor 140b provides a greater pressure drop and a higher steam flow rate than the first flow restrictor 140a.

In particular, in a two-valve, two-restrictor manifold 430 configuration (e.g., in case the third shutoff valve 134c is closed and/or the third flow restrictor 140c and third steam conduit 132c are omitted) the second flow restrictor 140b may generate more pressure drop than the first flow restrictor 140a, such that the second steam flow rate that is greater than the first steam flow rate. Therefore, the manifold 430 may provide a low steam flow rate when only the first shutoff valve 134a is open, an intermediate steam flow rate when only the second shutoff valve 134b is open, and a high steam flow rate when both the first and second shutoff valves 134a, 134b are open. The steam manifold 430 may provide no steam flow (e.g., a zero steam flow rate) when the first and second shutoff valves 134a, 134b are both closed. Accordingly, a two-valve, two-restrictor manifold 430 may provide 4 different flow rates (including a zero flow rate). A three-valve, three-restrictor manifold may provide 8 different flow rates (including a zero flow rate).

In some embodiments, the first steam flow rate may be less than the second steam flow rate. For example, the first steam flow rate may be a lower flow rate sufficient for startup and/or shutdown operations of the modules 200. For example, in some embodiments, the second steam flow rate may be from about 4 to about 8 times larger, such as from about 5 to about 7 times larger, or about 6 times larger, than the first steam flow rate. Thus, in the startup and shutdown modes, only the first shutoff valve 134a is open, and all steam passes through the first flow restrictor 140a to provide a low steam flow rate to the stack 100.

In some embodiments, the second steam flow rate may be sufficient for the normal steady-state mode operation of the modules 200. In other words, the second steam flow rate may be configured to prevent fuel starvation, while also maintaining a high fuel utilization rate during steady-state operation of the modules 200 (e.g., during steady-state hydrogen generation). Thus, in the steady-state operating mode, only the second shutoff valve 134b is open, and all steam passes through the second flow restrictor 140b to provide a medium steam flow rate to the stack 100. If it is desired to increase the steam flow rate to the stack 100, the first shutoff valve 134a is also opened to provide a high steam flow rate to the stack 100 through both the first and the second flow restrictors 140a and 140b.

When the steam manifold 430 includes the optional third flow restrictor 140c, the steam manifold 430 may provide 8 different steam flow rates, by opening different combinations of the first, second, and third shutoff valves 134a, 134b, 134c. The third steam flow rate may be based on a selected system operating condition. For example, the third steam flow rate may be greater than or less than the first steam flow rate or may be greater or less than the second steam flow rate, at a given incoming steam pressure.

In order for the manifolds 430 to provide a consistent steam flow rate, the pressure of the steam supplied to steam conduit 230 should be consistent and should be larger than a pressure drop generated by the components of the hotboxes 202 of the modules 200. In some embodiments, the steam conduit 230 may supply steam at a pressure of at least 15 psig, such as 15 to 50 psig, to the modules 200, in order to provide uniform steam mass flow through the steam manifold 430. The optional non-return valve 136 shown in FIG. 4 may be omitted if the shutoff valves 134a-134c and 234 prevent steam backflow.

FIG. 5A is a schematic view of an alternative electrolyzer system 500A, according to various embodiments of the present disclosure. The system 500A may be similar to the system 300. As such, only the difference therebetween will be discussed in detail.

Referring to FIGS. 2 and 5A, the system 500A may include steam manifolds 530 configured to control steam flow from the steam conduit 230 to the corresponding electrolyzer modules 200. The steam manifolds 530 may be located outside of the cabinets 204 of the electrolyzer modules 200, which may facilitate servicing of the steam manifolds 530.

Each steam manifold 530 may include a first shutoff valve 134a and first flow restrictor 140a fluidly connected by a first steam conduit 132a, and a second shutoff valve 134b and second flow restrictor 140b fluidly connected by a second steam conduit 132b. The first flow restrictor 140a may be configured to provide a first steam flow rate, and the second flow restrictor 140b may be configured to provide a second steam flow rate different from (e.g., larger than) the first steam flow rate. In some embodiments, the second steam flow rate may be suitable for steady-state operation of the corresponding module 200, and the first steam flow rate may be suitable for startup, shutdown, and/or standby operations of the corresponding module 200.

FIG. 5B is a schematic view of an alternative electrolyzer system 500B, according to various embodiments of the present disclosure. The system 500B may be similar to the system 500A. As such, only the difference therebetween will be discussed in detail.

Referring to FIG. 5B, the steam manifold 530 is located inside the cabinets 204 of the modules 200 of the system 500B. Furthermore, the first shutoff valve 134a on the first steam conduit 132a may be omitted. In this case, the module shutoff valve 234 located outside the module 200 cabinet 204 is used to control the steam flow through the first steam conduit 132a. If one module 200 is faulted and needs to be taken off line for replacement or servicing, then the module shutoff valve 234 of the faulted module 200 is closed to stop steam from flowing into the faulted module 200. The module shutoff valve 234 remains open for the remainder of the modules 200 to keep them operating during servicing or replacement of the faulted module 200. During startup or shutdown of the system 500B, the steam flows to the stacks 100 of the remaining (i.e., non-faulted) modules 200 through the first flow restrictor 140a, while the shutoff valve 134b on the second steam conduit 132b is closed. During steady-state operating mode, the shutoff valve 134b on the second steam conduit 132b is opened, and steam flows to the stacks 100 of the remaining (i.e., non-faulted) modules 200 through both the first and the second flow restrictors 140a and 140b. Thus, the servicing or replacement of the module 200 is made easier by locating the shutoff valve 234 outside the cabinet 204 of the module 200.

FIG. 6 is a schematic view of an alternative electrolyzer system 600, according to various embodiments of the present disclosure. The system 600 may be similar to the system 300. As such, only the difference therebetween will be discussed in detail.

Referring to FIG. 6, the system 600 may include steam manifolds 630 configured to control steam flow from the steam conduit 230 to each of the electrolyzer modules 200. In particular, the steam manifolds 630 may be located outside of the cabinets 204 of the electrolyzer modules 200, which may facilitate servicing of the steam manifolds 630. However, in other embodiments, the steam manifolds 630 may be located inside of the respective modules 200.

Each steam manifold 630 may comprise a first shutoff valve 134a located on a first steam conduit 132a, and a second shutoff valve 134b and a flow restrictor 140 located on a second steam conduit 132b. The first steam conduit 132a lacks a flow restrictor. The first shutoff valve 134a may control steam flow through the first steam conduit 132a to the corresponding module 200. Steam flowing through the first steam conduit 132a does not pass through a flow restrictor 140. In some embodiments, steam flow to the modules 200 through the steam conduit 230 and the first steam conduits 132a may be controlled by the primary steam valve 232, which may be a proportional valve.

The second shutoff valve 134b may control steam flow through the second steam conduit 132b to the corresponding module 200, with the steam flow rate being controlled by the flow restrictor 140. The flow restrictor 140 may be configured to provide a desired steam flow rate as described above.

In one embodiment, the second shutoff valves 134b are closed during the steady-state operating mode of all modules 200 at a designed steady-state hydrogen output. In this steady-state operating mode, the steam provided to the stacks 100 does not pass through a flow restrictor 140.

In case one of the modules 200 is faulted, and operates at less than a designed output, then the faulted module 200 is designated for future service or replacement, but continues to operate at a reduced hydrogen output prior to the service or replacement. In this operating mode, the first shutoff valves 134a are closed and the second shutoff valves 134b are opened, and all steam flows to the stacks 100 in all modules (including the faulted module) 200 through the respective flow restrictors 140 to provide a fixed amount of steam which is sufficient for a single operating mode until the faulted module 200 is repaired or replaced. The single operating mode may be selected based on the system 600 site design.

In one embodiment, the single operating mode comprises the normal steady-state operating mode for the non-faulted modules 200 to provide a designed steady-state hydrogen output. In this mode, the faulted module 200 will receive too much steam and will continue to operate at a lower than designed steam utilization. This may be compensated by cooling the steam using the product cooler 116 shown in FIG. 3A.

In another embodiment, the single operating mode comprises a reduced hydrogen production mode in which all modules 200 of the system 600 provide less than the designed steady-state hydrogen output. The controller 225 is configured to reduce the amount of power provided to the non-faulted modules 200 to match the reduced steam flow to these modules. This mode maintains the desired steam utilization rate for all modules 200, but at lower hydrogen production rate.

In yet another embodiment, the single operating mode comprises a modified steady-state operating mode in which the amount of steam provided to the modules 200 equals the amount of steam needed provide a designed steady-state hydrogen output minus the amount of steam provided during startup and shutdown modes.

Therefore, various embodiments allow for continued hydrogen product production prior to or during the time when a faulted electrolyzer module 200 is taken off line, repaired, replaced, and/or restarted. Until the repaired or replaced module 200 is ramped up to the steady-state operating temperature and ready to start hydrogen production, the remaining modules 200 may receive steam through the flow restrictors 140 or directly through the first steam conduit 132a, depending on the design of the system.

The electrolyzer systems of various embodiments of the present disclosure provide a benefit to the climate by reducing greenhouse gas emissions.

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 guiding 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.