SYSTEM AND METHOD FOR REDUCING IMPURITY BUILDUP IN ELECTROLYZER SYSTEMS

Description

FIELD

The embodiments of the present invention are generally directed to electrolyzer systems and methods of operating the same, and more particularly to reducing or preventing impurity buildup in electrolyzer systems.

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, a method of operating an electrolyzer system includes providing steam to a stack of electrolyzer cells through a steam filter, electrolyzing the steam into a hydrogen product in the stack of electrolyzer cells, receiving data from one or more sensors indicating that the steam filter requires cleaning or replacement, and cleaning or replacing the steam filter in response to the receiving the data from the one or more sensors indicating that the steam filter requires cleaning or replacement.

In various embodiments, a method of operating an electrolyzer system includes vaporizing water into steam in a steam generator, providing the steam from the steam generator to a stack of electrolyzer cells through a steam conduit, electrolyzing the steam into a hydrogen product in the stack of electrolyzer cells, receiving data indicating that the steam generator requires cleaning or replacement, and cleaning or replacing the steam generator in response to the receiving the data indicating that the steam generator requires cleaning or replacement.

In various embodiments, an electrolyzer system includes a steam conduit connecting a steam supply to a stack of electrolyzer cells, a steam filter located in the steam conduit such that steam in the steam conduit flows through the steam filter, and one or more sensors configured transmit data indicating that the steam filter requires cleaning or replacement.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a perspective view of an electrolyzer cell stack.

FIG. 1B is a side cross-sectional view of a portion of the stack of FIG. 1A.

FIG. 2A is a schematic view of an electrolyzer system according to a first embodiment of the present disclosure.

FIG. 2B is a schematic view of an electrolyzer system according to second embodiment of the present disclosure.

FIG. 3 is a cut away view of a steam generator for an electrolyzer system of the second embodiment 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.

An electrolyzer cell stack receives steam supplied from a steam source. The steam source may comprise a building or factory steam source (e.g., external boiler, etc.), which provides byproduct steam to the electrolyzer cell stack, and/or a dedicated steam generator which is part of an electrolyzer system.

The water used to generate the steam may be purified in various ways, including being de-ionized, softened, etc. Nevertheless, residual impurities are likely to be present in the water after purification. Such impurities may precipitate out of the water when it is converted into steam and then precipitate as solid particles in the steam generator and/or throughout the electrolyzer system, which may reduce the life span and effectiveness of the steam generator and/or the electrolyzer system. The systems and methods of the embodiments of the present disclosure reduce or prevent damage to the electrolyzer system and/or the steam generator caused by precipitation of solid impurities from the steam by detecting the buildup of the impurities before the devices in the system fail or have their performance degraded below an acceptable level.

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, and a fuel (i.e., steam) electrode 7. The stack 100 also includes internal steam/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 respective fuel side ribs 12A and air side ribs 12B that at least partially define steam channels 8A and air channels 8B. The interconnect 10 may operate as a separator that separates the steam side of one cell 1 from the air side of an adjacent cell 1. The air flow to the air electrode 3 serves as a sweep gas to entrain the oxygen ions transported through the electrolyte 5 by electrolysis. At either end of the stack 100, there may be an air end plate or a fuel end plate (not shown) for providing air or steam, 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., Crofert 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) may be used.

FIG. 2A is a schematic view an electrolyzer system 200A, according to a first embodiment of the present disclosure. Referring to FIGS. 1A, 1B, and 2A, the electrolyzer system 200A may include an electrolyzer cell (e.g., SOEC) stack 100, as described with respect to FIGS. 1A and 1B. The electrolyzer system 200A may also include a steam recuperator heat exchanger 108, a steam heater 110, an air recuperator heat exchanger 112, an air heater 114, and an optional product cooler/air preheater heat exchanger 111. The electrolyzer system 200A may also include a mixer 106 configured to receive steam from a steam source 150 and hydrogen from a hydrogen source 52 (e.g., a hydrogen storage vessel) 52 and to mix the steam with the hydrogen.

The electrolyzer system 200A may include a hotbox 210 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 210 may include multiple stacks 100 and an additional optional stack heater or heaters. The stacks 100 may be arranged in columns or column segments which receive electric power from an electric power source (e.g., a power grid, etc.) Each column may include one or more stacks 100. The product cooler/air preheater heat exchanger 111 can be located inside the hotbox 210, or it can be located outside of the hotbox 202. The mixer 106, the steam source 150, the hydrogen source 52, and a hydrogen processor 120 may be located external to the hotbox 210, as shown in FIG. 2A.

In an embodiment, the steam source 150 may comprise an external source of steam (e.g., a boiler of a building, an industrial steam source that generates steam as a byproduct of an industrial process, etc.) that is supplied to the mixer 106 via a steam conduit 151. Other steam sources may also be used. The steam conduit 151 carrying the steam from the steam source 150 may include a filter 155 which may trap (e.g., absorb, adsorb, etc.) various impurities in the steam. Impurities may include sand, sediment, silt, minerals (e.g., metal oxides, carbonates and/or nitrates), metals, chlorine, chlorine compounds, and/or organic matter.

The filter 155 may be a replaceable filter or a cleanable filter that may be removed and/or chemically cleaned for reuse. The chemical cleaning may comprise a chemical flush, such as an acid flush (e.g., nitric acid flush), that is either performed while the filter 155 is located in-situ in the steam conduit 151 and/or after the filter is removed from the steam conduit 151. The filter 155 may comprise any suitable type of steam filter, such as a sintered metal filter (e.g., filter formed from sintered metal powder), a pleated metal mesh filter (e.g., filter formed by weaving metal wires into a mesh), or a pleated-sintered metal filter (e.g., filter formed of sintered, pleated metal microfibers). The filter 155 may be formed of stainless steel (e.g., stainless steel 316) or another metal or metal alloy. The filter 155 may optionally include a catalyst coating to react with impurities and/or convert impurities into more capturable forms (e.g., ions).

At least one sensor 157, such as a pressure sensor, a flow rate sensor and/or a temperature sensor, may be located on the steam conduit 151 upstream and/or downstream of the filter 155. The at least one sensor 157 may indicate when the filter 155 requires replacement (e.g., based on a pressure drop and/or a flow rate drop of the steam in the conduit 151). The output of the sensor 157 may be connected to a controller 122 via a wired or a wireless data connection. For example, the sensor 157 may comprise a pressure sensor or a flow rate sensor located downstream of the filter 155 or a differential pressure sensor located upstream and downstream of the filter 155. The sensor 157 outputs data regarding the steam pressure or flow rate downstream of the filter 155 or a differential pressure (i.e., a pressure difference) between pressures measured upstream and downstream of the filter 155. The filter 155 may be replaced or cleaned (e.g., chemically cleaned) periodically, based on one or more of: (a) fixed time interval (e.g. a certain number of times per year, such as once per year) or (b) measurements of the steam pressure, flow rate and/or differential pressure from the sensor 157. For example, when the measured steam pressure or flow rate decreases below a low threshold value, and/or the differential pressure increases above a high threshold value, the controller 122 sends a signal to control personnel to replace or clean the filter 155.

During operation, the stack 100 may be provided with steam and electric power (e.g., current or voltage) from an external power source. In particular, the steam may be provided to the steam electrodes 7 of the electrolyzer cells (e.g., SOECs) 1 of the stack 100, and the power source may apply a voltage between the steam electrodes 7 and the air electrodes 3 of the stack 100, in order to electrochemically split water molecules and generate hydrogen (e.g., H₂) and oxygen (e.g., O₂). Air may also be provided to the air electrodes 3, in order to sweep the oxygen from the air electrodes 3. As such, the stack 100 may output a main hydrogen product stream and an oxygen-rich exhaust stream, such as an oxygen-rich air stream (“oxygen exhaust stream”).

FIG. 2B is a schematic view of an electrolyzer system 200B, according to a second embodiment of the present disclosure. The electrolyzer system 200B includes a dedicated steam generator 104 which generates steam from water provided to the steam generator from a water source 50 instead of the steam provided from the steam source 150 of the first embodiment. The electrolyzer system 200B may also include an optional water preheater 102.

The water preheater 102 and the steam generator 104 may be located external to the hotbox 210, as shown in FIG. 2B. Alternatively, the water preheater 102 and/or the steam generator 104 may be located inside the hotbox 210. In another alternative embodiment, the water preheater 102 may be located inside the hotbox 210 and the steam generator 104 may be located outside the hotbox 210.

In order to generate the steam, water may be provided to the electrolyzer system 200B from the water source 50 via a water inlet conduit 101. The water may be deionized (DI) water that is deionized as much as is practical (e.g., <0.1 μS/cm, or at least <1 μS/cm), in order to prevent and/or minimize scaling during vaporization. In some embodiments, the water source 50 may include deionization beds. In various embodiments, the electrolyzer system 200B may include a water flow control device (not shown), such as a mass flow controller, a positive displacement pump, a control valve/water flow meter, or the like, in order to provide a desired water flow rate to the electrolyzer system 200B.

If the electrolyzer system 200B includes the water preheater 102, the water may be provided from the water source 50 to the water preheater 102 via a water inlet conduit 101. The water preheater 102 may be a heat exchanger configured to heat the water using heat recovered from the oxygen exhaust stream output from the air recuperator heat exchanger 112 via an air exhaust conduit 103. A portion of the water may vaporize in the water preheater 102. The water output from the water preheater 102 or the water source 50 may be provided to the steam generator 104 via the water conduit 101. The steam generator 104 may be configured to heat the water not vaporized in the water preheater 102 (if present) to convert the water into steam. The steam generator 104 may include a heating element to vaporize the water and generate the steam. For example, the steam generator 104 may include an AC or DC resistance heating element or an induction heating element. These aspects of the steam generator 104 are described with respect to FIG. 3 below.

If the mixer 106 is present, the steam may be provided from the steam generator 104 to the mixer 106 via the steam conduit 151 prior to being provided to the steam recuperator 108 from the mixer 106 via the steam inlet conduit 107. Alternatively, if the electrolyzer system 200B does not include a mixer 106, steam output from the steam generator 104 may be provided to the steam recuperator heat exchanger 108 via the steam conduit 151 and the steam inlet conduit 107.

The steam may include small amounts of dissolved air and/or oxygen. As such, the mixer 106 may be configured to mix the steam with hydrogen gas in order to maintain a reducing environment in the stack 100, and in particular, at the fuel electrodes 7. Specifically, the mixer 106 may be configured to mix the steam with the hydrogen received from the hydrogen source 52 via a hydrogen inlet conduit 109 and/or with a portion of the hydrogen product stream output from the stack 100 via the recycling conduit 117. The hydrogen source 52 may be a low and/or intermediate pressure storage tank for providing pressurized hydrogen to the stack 100 via the hydrogen inlet conduit 109 and the mixer 106. The steam conduit 151 may include a filter 155 and one or more sensors 157, as described above regarding FIG. 2A.

In some embodiments, the hydrogen may be provided by the external hydrogen source 52 during the electrolyzer system startup, shutdown and emergency (e.g., fault) operating modes when the electrolyzer system 200A or 200B is not generating hydrogen. For example, during startup, the hydrogen may be provided from the hydrogen source 52, and during steady-state, the hydrogen may be provided by diverting a portion of the hydrogen product stream (i.e., hydrogen exhaust stream) that is generated by the stack 100 from the main product conduit 115 to the mixer 106. In particular, the electrolyzer system 200A or 200B may include a hydrogen separator 116, such as a splitter, pump, blower and/or valve, configured to divert a portion of the generated hydrogen product stream flowing from the stack 100 through main product conduit 115 to the mixer 106 during steady-state operation. In particular, the separator 116 may be fluidly connected to the mixer 106 by the recycling conduit 117. An optional recycle blower 121 may be located on the recycle conduit 117.

The steam recuperator heat exchanger 108 may be a heat exchanger configured to recover heat from the hydrogen stream output from the stack 100. The steam output from the steam recuperator heat exchanger 108 may be provided to the steam heater 110 which is located downstream from the steam recuperator heat exchanger 108, as shown in FIGS. 2A and 2B. 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.

The oxygen exhaust stream output from the stack 100 may be provided to the air recuperator heat exchanger 112. The air recuperator heat exchanger 112 may be provided with ambient air by an air blower 118 via an air conduit 119. The air recuperator heat exchanger 112 may be configured to heat the air using heat extracted from the oxygen exhaust stream flowing through the exhaust conduit 103. In some embodiments, the ambient air may be filtered to remove contaminants prior to being provided to the air recuperator heat exchanger 112 or the air blower 118. Air output from the air recuperator heat exchanger 112 may be provided to the air heater 114. The air heater may include a resistive or inductive heating element configured to heat the air to a temperature exceeding the operating temperature of the stack 100.

In one embodiment, the electrolyzer system 200A or 200B may include an optional product cooler/air preheater heat exchanger 111 located inside or outside of the hotbox 210. In particular, the product cooler/air preheater heat exchanger 111 may be configured to preheat air flowing through the air conduit 119 to the hotbox 210 from the air blower 118 using heat from the product hydrogen and residual steam mixture exiting the steam recuperator heat exchanger 108 via the main product conduit 115.

The hydrogen stream output from the hydrogen separator 116 via the main product conduit 115 may be compressed and/or purified in an optional hydrogen processor 120, in order to remove from about 70% to about 90% of the hydrogen from the hydrogen product stream. A remaining unpumped effluent from the hydrogen pump is a water rich stream that is already fully vaporized.

In various embodiments, the hydrogen processor 120 may include at least one electrochemical hydrogen pump, liquid ring compressor, diaphragm compressor, other compression device, or combination thereof. For example, the hydrogen processor may include a series of electrochemical hydrogen pumps, which may be disposed in series and/or in parallel with respect to a flow direction of the hydrogen stream, in order to separate and compress the hydrogen stream. The electrochemical hydrogen pumps may comprise high temperature hydrogen pumps that operate at a temperature of from about 120° C. to about 150° C. The final product from compression may still contain traces of water. As such, the hydrogen processor 120 may include a dewatering device, such as a condenser, a temperature swing adsorption reactor or a pressure swing adsorption reactor, to remove this residual water, if necessary. The electrolyzer system 200B may be configured to repurify (e.g., in DI beds) the residual water and provide the residual water removed from the compressed hydrogen stream to the water preheater 102.

According to various embodiments, the electrolyzer system 200A or 200B may include a controller 122, such as a central processing unit, which is configured to control the operation of the system. For example, the controller 122 may be wired or wirelessly connected to various elements (e.g., valves, blower(s), power source, etc.) of the electrolyzer system 200A or 200B to control the same. The controller 122 may be connected to the sensor(s) 157 via a wired or a wireless data connection, and may provide an alert to service personnel to change or clean the filter 155.

In one embodiment, the electrolyzer system 200A or 200B may comprise an entire electrolyzer system. In another embodiment, the electrolyzer system 200A or 200B may comprise a portion of a larger electrolyzer system. For example, the hotbox 210, the mixer 106, the product cooler/air preheater heat exchanger 111, the splitter 116, the air blower 118 and the recycle blower 121 may be located in a cabinet of an electrolyzer module, while the remaining components may be located in one or more additional cabinets or outside of the electrolyzer system 200A or 200B. The electrolyzer system 200A or 200B may include multiple electrolyzer modules located in separate cabinets and fluidly connected to the steam source 150 or the water source 50, the hydrogen source 52 and the hydrogen processor 120.

FIG. 3 illustrates an exemplary steam generator 104 that may be used in the electrolyzer systems 200A or 200B. The steam generator 104 may include an electronics enclosure 302, one or more heating elements 304, a heater enclosure 306, one or more steam conduits 308, and one or more sensors 310 and 312. The heating elements 304 may comprise resistive heating elements. The one or more steam conduits 308 may comprise one or more stainless steel steam flow tubes 308A, 308B in a single tube, dual tube parallel or dual tube series configuration. The steam conduits 308 may be arranged as spiral that wraps around the heating elements 304 in the heater enclosure 306. The one or more sensors 310 and 312 may comprise thermocouple temperature sensors. The sensors 310 and 312 may be located in thermowells adjacent to the one or more heating elements 304 (e.g., embedded in a heater body). The sensors 310, 312 may detect a temperature of the heating elements 304 and provide the detected temperature to a steam generator controller located in the electronics enclosure 302. Other steam generator 104 configurations may also be used.

The water from the water source 50 may flow via the water conduit 101 and enter the steam conduits 308 at the bottom of the steam generator 104. The steam may exit the steam conduits 308 at the top of the steam generator 104. Alternatively, the water may flow through the steam conduits 308 downward, generally horizontally, or in any other direction. Over time, impurities may precipitate out of the water as the water is turned to steam, such that the impurities settle in the steam conduits 308. This reduces the water and steam flow rate through the steam generator 104 and degrades the steam generation capability of the steam generator 104.

The system controller 122 may receive telemetry data from the steam generator 104 controller via a wired or wireless data connection. The steam generator 104 may be cleaned or replaced based on the telemetry data received by the system controller 122 from the sensors 310, 312 and/or 157. For example, if the telemetry data from the temperature sensors 310 and/or 312 indicates that the steam generator 104 requires a heating element 304 temperature that is above a high threshold temperature value to maintain a predetermined steam flow, and/or if the steam pressure and/or flow rate from the pressure or flow rate sensor 157 located upstream of the filter 155 is below a low threshold value, then the system controller 122 may send a signal to control personnel to replace or chemically clean the steam generator 104. The steam generator 104 may be chemically cleaned on site by flushing the steam conduits 308 with a chemical flush (e.g., a nitric acid flush) to remove the precipitated impurities.

Electrolyzer systems of the embodiments of the present disclosure are designed to reduce greenhouse gas emissions and have a positive impact on the climate.

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.