Electrolyzer system with steam generator and method of operation thereof

Abstract

To provide an electrolytic tank system including solid oxide type electrolytic cells (SOEC), and a method of operating the same.SOLUTION: The electrolytic tank system includes: a stack of solid oxide type electrolytic cells configured to receive steam and to discharge hydrogen exhaust and oxygen exhaust; an auxiliary steam generator configured to generate steam to be supplied to the stack by vaporizing water using heat obtained from the oxygen exhaust; a water preheater configured to preheat water using heat obtained from the oxygen exhaust; and a primary steam generator configured to generate steam to be supplied to the stack by vaporizing water preheated by the water preheater.SELECTED DRAWING: Figure 3B

Description

[Technical Field]

[0001] Priority This application is a utility patent application claiming the benefit of U.S. Provisional Application No. 63 / 222,555, filed July 16, 2021, the entire contents of which are incorporated herein by reference.

[0002] SUMMARY OF THE INVENTION Embodiments of the present invention are generally directed to electrolyzer systems including solid oxide electrolysis cells (SOECs) and methods of operating the same. [Background technology]

[0003] A solid oxide fuel cell (SOFC) can be operated as an electrolyzer to produce hydrogen and oxygen, which is called a solid oxide electrolysis cell (SOEC). In SOFC mode, oxide ions are transported from the cathode side (air) to the anode side (fuel), and the driving force is the chemical gradient of oxygen partial pressure across the electrolyte. In SOEC mode, a positive potential is applied to the air side of the cell, causing oxide ions to be transported from the fuel side to the air side. Because the cathode and anode are reversed between SOFCs and SOECs (i.e., the SOFC cathode is the SOEC anode, and the SOFC anode is the SOEC cathode), hereafter the SOFC cathode (SOEC anode) will be referred to as the air electrode, and the SOFC anode (SOEC cathode) will be referred to as the fuel electrode. During SOEC mode, water in the fuel stream is reduced (HO + 2e → O 2- +H2), H2 gas and O 2- Forms ions. O 2- The ions are transported through the solid electrolyte and then oxidized on the air side (O 2- The open circuit voltage of an SOFC operating on air and a moist fuel (hydrogen, reformed natural gas) is on the order of 0.9–1 V (depending on the water content), so a positive voltage applied to the air electrode in SOEC mode increases the cell voltage to the normal operating voltage of 1.1–1.3 V. Summary of the Invention

[0004] In various embodiments, the electrolyzer system includes a stack of solid oxide electrolysis cells configured to receive steam and output a hydrogen exhaust and an oxygen exhaust; an auxiliary steam generator configured to generate steam supplied to the stack by vaporizing water using heat obtained from the oxygen exhaust, typically enriched air having a higher oxygen content than normal air; a water preheater configured to preheat water using heat obtained from the oxygen exhaust; and a primary steam generator configured to generate steam supplied to the stack by vaporizing water preheated by the water preheater.

[0005] In various embodiments, a method of operating an electrolyzer system includes generating steam by vaporizing water supplied to an auxiliary steam generator using heat obtained from an oxygen exhaust, the water being supplied to the auxiliary steam generator; generating preheated water by heating water supplied to a water preheater using heat obtained from the oxygen exhaust; generating steam by vaporizing the preheated water in a primary steam generator; and generating hydrogen exhaust and oxygen exhaust using a stack of solid oxide electrolysis cells using steam generated by the primary steam generator and the auxiliary steam generator. [Brief explanation of the drawings]

[0006] [Figure 1A] FIG. 1A is a perspective view of a solid oxide electrolysis cell (SOEC) stack. [Figure 1B] FIG. 1B is a vertical cross-sectional view of a portion of the stack of FIG. 1A.

[0007] [Figure 2] FIG. 2 is a schematic diagram illustrating the process flow through an electrolytic cell system according to various embodiments of the present disclosure.

[0008] [Figure 3A] FIG. 3A is a schematic diagram illustrating the process flow in an alternative electrolyzer system according to various embodiments of the present disclosure.

[0009] [Figure 3B] FIG. 3B is a schematic diagram illustrating the process flow in another alternative electrolyzer system according to various embodiments of the present disclosure.

[0010] [Figure 3C] FIG. 3C is a schematic diagram illustrating the process flow in another alternative electrolyzer system according to various embodiments of the present disclosure.

[0011] [Figure 3D] FIG. 3D is a schematic diagram illustrating the process flow in another alternative electrolyzer system according to various embodiments of the present disclosure.

[0012] [Figure 4A] FIG. 4A is a perspective view of a hot box according to various embodiments of the present disclosure. [Figure 4B] FIG. 4B is a perspective view of the hot box with the outer shell removed.

[0013] [Figure 5A] FIG. 5A is a cross-sectional view of the hot box of FIGS. 4A and 4B according to various embodiments of the present disclosure. [Figure 5B] FIG. 5B is a cross-sectional view of the hot box showing the components located inside the central column. [Figure 5C] FIG. 5C is a partial perspective view showing the steam recuperator and air preheater elements of the hot box. [Figure 5D] FIG. 5D is a perspective view of the hot box distribution hub.

[0014] [Figure 6] FIG. 6 is a cross-sectional perspective view of a central column 320 including a modified steam generator 404 according to various embodiments of the present disclosure.

[0015] [Figure 7AB]7A is a cross-sectional perspective view of a central column and an external steam generator according to various embodiments of the present disclosure, and FIG. 7B is an enlarged partial cross-sectional view of the steam generator of FIG. 7A. [Figure 7C] FIG. 7C is a perspective view of an external steam generator according to an alternative embodiment of the present disclosure. [Figure 7DE] 7D is a perspective view of an external steam generator according to an alternative embodiment of the present disclosure, and FIG. 7E is a perspective view of an external steam generator according to an alternative embodiment of the present disclosure. [Figure 7F] FIG. 7F is a perspective view of an external steam generator according to an alternative embodiment of the present disclosure.

[0016] [Figure 8A] FIG. 8A is a perspective view illustrating a heating element configuration according to various embodiments of the present disclosure. [Figure 8B] FIG. 8B is a perspective view illustrating a heating element configuration according to various embodiments of the present disclosure. [Figure 8C] FIG. 8C is a perspective view illustrating a heating element configuration according to various embodiments of the present disclosure. [Figure 8D] FIG. 8D is a perspective view illustrating a heating element configuration according to various embodiments of the present disclosure. [Figure 8E] FIG. 8E is a perspective view illustrating a heating element configuration according to various embodiments of the present disclosure. [Figure 8F] FIG. 8F is a perspective view illustrating a heating element configuration according to various embodiments of the present disclosure.

[0017] [Figure 9A] FIG. 9A is a schematic diagram illustrating an air heater having a zone configuration according to various embodiments of the present disclosure. [Figure 9B] FIG. 9B is a perspective view showing the heating element of the air heater of FIG. 9A.

[0018] [Figure 10A] FIG. 10A is a cross-sectional view of a central column including a modified steam heating element according to various embodiments of the present disclosure. [Figure 10B] FIG. 10B is an enlarged portion of FIG. 10A.

[0019] [Figure 11] FIG. 11 is a cross-sectional perspective view illustrating air flow through a modified hot box according to various embodiments of the present disclosure.

[0020] [Figure 12] FIG. 12 is a cross-sectional perspective view illustrating air flow through a modified hot box according to various embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0021] Figure 1A is a perspective view of a solid oxide electrolysis cell (SOEC) stack 100, and Figure 1B is a vertical cross-sectional view of a portion of the stack 100 of Figure 1A. Referring to Figures 1A and 1B, the stack 100 includes multiple electrolysis cells 1 separated by interconnects 10, also called gas flow separator plates or bipolar plates. Each electrolysis cell 1 includes an air electrode 3, a solid oxide electrolyte 5, and a fuel electrode 7. The stack 100 also includes an internal fuel riser channel 22.

[0022] Each interconnect 10 electrically connects adjacent electrolysis cells 1 in the stack 20. In particular, an interconnect 10 can electrically connect the fuel electrode 7 of one electrolysis cell 1 to the air electrode 3 of an adjacent electrolysis cell 1. FIG. 1B shows the lower electrolysis cell 1 positioned between two interconnects 10.

[0023] Each interconnect 10 includes ribs 12 that at least partially define fuel channels 8A and air channels 8B. The interconnects 10 can operate as gas-fuel separators, separating the fuel / vapor flowing to the fuel electrode 7 of one electrolysis cell 1 in the stack 20 from the air flowing to the air electrode 3 of an adjacent electrolysis cell 1 in the stack 20. The optional air flow acts as a sweep gas to entrain O transported by the electrolyte. At either end of the stack 100, there may be air or fuel end plates (not shown) to supply air or fuel, respectively, to the end electrodes.

[0024] 2 is a schematic diagram illustrating process flow within an electrolyzer system 200 according to various embodiments of the present disclosure. Referring to FIGURES 1A, 1B, and 2, the system 200 may include an electrolysis cell (SOEC) stack 100 including multiple solid oxide electrolysis cells (SOECs), as described with respect to FIGURES 1A and 1B. The system 200 may also include a steam generator 104, a steam recuperator 108, a steam heater 110, an air recuperator 112, and an air heater 114. The system 200 may also include an optional water preheater 102 and an optional mixer 106.

[0025] System 200 may include a hot box 300 for housing various components, such as stack 100, steam recuperator 108, steam heater 110, air recuperator 112, and / or air heater 114. In some embodiments, hot box 300 may include multiple stacks 100. Water preheater 102 and steam generator 104 may be located outside hot box 300, as shown in FIG. 2 . Alternatively, water preheater 102 and / or steam generator 104 may be located inside hot box 300. In another alternative, water preheater 102 may be located inside hot box 300, and steam generator 104 may be located outside hot box 300 (not shown). As will be readily understood, other configurations are possible without departing from this invention.

[0026] During operation, stack 100 may be supplied with steam and an electric current or voltage from an external power source. In particular, steam may be supplied to fuel electrode 7 of electrolysis cell 1 of stack 100, and a power source may apply a voltage between fuel electrode 7 and air electrode 3 to electrochemically split water molecules and produce hydrogen (e.g., H) and oxygen (e.g., O). Air may also be supplied to air electrode 3 to sweep oxygen from air electrode 3. Thus, stack 100 may output a hydrogen stream and an oxygen-enriched exhaust stream ("oxygen exhaust stream"), such as an oxygen-enriched air stream.

[0027] To generate steam, water may be supplied to system 200 from water source 50. The water may be deionized (DI) water, deionized to the extent practicable (e.g., <0.1 μS / cm, or at least <1 μS / cm) to prevent and / or minimize scaling during evaporation. In some embodiments, water source 50 may include a deionized bed. In various embodiments, system 200 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, etc., to provide a desired water flow rate to system 200.

[0028] If system 200 includes a water preheater 102, water may be supplied to the water preheater 102 from a water source 50. The water preheater 102 may be a heat exchanger configured to heat water using heat recovered from the oxygen exhaust stream. Preheating the water may reduce the overall power consumption of the system 200 per unit of hydrogen produced. In particular, the water preheater 102 may be configured to recover heat from the oxygen exhaust stream that may not be recovered by the air recuperator 112, as described below. The oxygen exhaust stream may exit the water preheater 102 at a temperature greater than 80°C, such as greater than 100°C, e.g., at a temperature of about 110°C-120°C.

[0029] Water from the water preheater 102 or the water source 50 may be supplied to the steam generator 104. A portion of the water may be vaporized in the water preheater. The steam generator 104 may be configured to heat water that is not vaporized in the water preheater and convert the water into steam. For example, the steam generator 104 may include a heating element to vaporize the water and generate steam. For example, the steam generator 104 may include an AC or DC resistance heating element, or an induction heating element.

[0030] The steam generator 104 may include multiple zones / elements, which may or may not be mechanically separated. For example, the steam generator 104 may include a pre-boiler for heating water to or near the boiling point. The steam generator 104 may also include a vaporizer configured to convert the pre-boiled water into steam. The steam generator 104 may also include a degasser for providing a relatively small steam purge to remove dissolved air from the water prior to bulk vaporization. The steam generator 104 may also include an optional superheater configured to further increase the temperature of the steam generated in the vaporizer. The steam generator 104 may include a device such as a demister pad located downstream of the heating element and / or upstream from the superheater. The demister pad may be configured to minimize liquid water entrainment in the steam discharged from the steam generator 104 and / or supplied to the superheater.

[0031] If the steam product is superheated, heat loss to the ambient environment will discourage condensation downstream of the steam generator 104. Avoiding condensation is preferable because condensed water tends to form slugs of water, which can cause large fluctuations in the mass flow delivered over time. Avoiding excessive superheating can also be beneficial to limit the total power consumption of the system 200. For example, the steam may be superheated by an amount ranging from about 10°C to about 100°C.

[0032] Blowdown from the steam generator 104 can be beneficial for long-term operation because the water will likely contain some mineralization after deionization. Typical liquid blowdown can be on the order of 1%. Blowdown can be continuous or intermittent, for example, 10x steady state flow for 6 seconds every minute, 5x steady state flow for 1 minute every 5 minutes, etc. Pumping the blowdown to the hot oxygen exhaust can eliminate the need for a blowdown stream.

[0033] Steam exiting the steam generator 104 may be supplied to the steam recuperator 108. However, if the system 200 includes the optional mixer 106, the steam may be supplied to the mixer 106 before being supplied to the steam recuperator 108. In particular, the steam may contain small amounts of dissolved air and / or oxygen. Thus, the mixer 106 may be configured to mix the steam with hydrogen gas to maintain a reducing environment within the stack 100, particularly at the fuel electrode 7.

[0034] The mixer 106 can be configured to mix the steam with hydrogen received from the hydrogen storage device 52 and / or with a portion of the hydrogen stream exiting the stack 100. The hydrogen addition rate can be set to provide an amount of hydrogen in excess of the amount of hydrogen required to react with the amount of oxygen dissolved in the steam. The hydrogen addition rate can be fixed, or a constant ratio of water to hydrogen can be set. However, if the steam is formed using fully degassed water, the mixer 106 and / or the addition of hydrogen can optionally be omitted.

[0035] In some embodiments, hydrogen may be supplied by an external hydrogen source during startup and / or steady-state operation of the system. For example, during startup, hydrogen may be supplied from the hydrogen storage device 52, and during steady-state operation, hydrogen may be supplied from the hydrogen storage device 52 and / or by diverting a portion of the hydrogen stream produced by the stack 100 (i.e., the hydrogen exhaust stream) to the mixer 106. In particular, the system 200 may include a hydrogen separator 116, such as a splitter, pump, blower, and / or valve, configured to selectively divert a portion of the produced hydrogen stream to the mixer 106 during steady-state operation.

[0036] The steam recuperator 108 may be a heat exchanger configured to recover heat from the hydrogen stream exiting the stack 100. Thus, the steam recuperator 108 may be configured to increase the efficiency of the system 200. The steam may be heated in the steam recuperator 108 to a range between 600°C and 830°C. In some examples, the steam is heated to within 10°C and 150°C of the stack operating temperature. For example, the stack operating temperature may be 700°C or 750°C, or therebetween, and the steam may be heated in the steam recuperator 108 to at least 600°C, such as 650°C and 740°C. The steam from the steam recuperator 108 is below the average stack operating temperature (e.g., in the range of 10 to 100°C).

[0037] The steam exiting the steam recuperator 108 may be supplied to a steam heater 110 located downstream of the steam recuperator 108, as shown in FIG. 2A. The steam heater 110 may include a heating element, such as a resistance or induction 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 in the range of about 900°C to about 1200°C, e.g., 920°C to 980°C. At lower stack temperatures between 700°C and 750°C, the steam heater outlet temperature may be as low as 700°C. Thus, the stack 100 may be supplied with steam or a steam-hydrogen mixture at a temperature that enables efficient hydrogen production. Heat may also be transferred directly from the steam heater to the stack by radiation (i.e., by radiative heat transfer). In some embodiments, the steam heater 110 is optional and heat is obtained via the air heater 114 .

[0038] In another alternative embodiment, steam heater 110 may include a heat exchanger configured to heat steam using heat obtained from a high-temperature fluid, such as a fluid heated to about 900° C. or higher. This fluid may be supplied from a power plant, such as a solar concentrator farm or a nuclear reactor power plant. Alternatively, if the fluid is high-temperature steam, such as steam supplied from a nuclear reactor power plant, such steam may be supplied to fuel electrodes 7 of stack 100. In this case, water source 50 may include a high-temperature steam source, and one or more of water preheater 102, steam generator 104, steam recuperator 108, and / or steam heater 110 may be omitted.

[0039] In some embodiments, the steam heater 110 may include multiple steam heater zones (divided vertically or circumferentially or both) with independent power levels to enhance thermal uniformity.

[0040] In some embodiments, the operation of the steam recuperator 108 and the steam heater 110 can be combined into a single component. For example, the steam recuperator 108 can include a voltage source configured to apply a voltage to heat exchange fins of the steam recuperator 108, such that the heat exchange fins act as resistive heating elements to heat the steam to a temperature high enough to be supplied to the stack 100. This can be any temperature above the stack operating temperature, for example, a temperature in the range of about 800°C to about 1200°C. The high-temperature steam (or optionally a steam / hydrogen mixture) exiting the steam heater 110 can be supplied to the fuel electrode 7 of the stack 100.

[0041] The oxygen exhaust from the stack 100 may be supplied to an air recuperator 112. The air recuperator 112 may be supplied with ambient air by an air blower 118. The air recuperator 112 may be configured to heat the air using heat obtained from the oxygen exhaust. In some embodiments, the ambient air may be filtered to remove contaminants before being supplied to the air recuperator 112 or the air blower 118.

[0042] The air exiting the air recuperator 112 may be supplied to an air heater 114. The air heater may include a resistance or induction heating element configured to heat the air 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 air heater 114 may heat the air to a temperature in the range of about 900°C to about 1200°C, such as 920°C to 980°C. At lower stack temperatures, the air heater temperature may be as low as 800°C. Thus, the stack 100 may be supplied with air at a temperature that enables efficient hydrogen production. Heat may be transferred directly from the air heater to the stack by radiation.

[0043] The higher the temperature output from the air recuperator, the less power required for the air heater 114. An increase in pressure drop on either side of the air recuperator 112 can be countered by increasing the power of the air blower 118. Increasing the pressure drop aids in circumferential mass flow uniformity, creating a more uniform heat transfer environment and allowing for a higher temperature of the air inlet flow exiting the air recuperator 112. Increasing the pressure drop also increases the local heat transfer coefficient, thereby increasing the average exit temperature from the air recuperator 112.

[0044] In an alternative embodiment, the air heater 114 may include a heat exchanger configured to heat the air using heat obtained from a high temperature fluid, such as a fluid heated to about 900° C. or higher. This fluid may be supplied, for example, from a solar concentrating farm or a nuclear reactor.

[0045] In some embodiments, the air heater 114 may include multiple air heater zones (divided vertically or circumferentially, or both) with independent power levels to enhance thermal uniformity. In some embodiments, the air heater 114 may be located below the air recuperator 112, or between the stack 100 and the steam recuperator 108, or both. The air heater 114 may include a baffle with different sized slits at different heights along the baffle, allowing the air to exit the air heater 114 approximately uniformly in both temperature and height at all heights along the air heater 114. Air from the air heater 114 is supplied to the air electrodes 3 of the stack 100.

[0046] In some embodiments, the air recuperator 112 and the air heater 114 can be combined into a single component. For example, the air recuperator 112 can include a voltage source configured to apply a voltage to heat exchange fins of a heat exchanger included in the air recuperator 112 combined component, such that the fins act as resistive heating elements to heat the air to a temperature high enough to be supplied to the stack 100. This can be any temperature above the stack operating temperature, for example, a temperature in the range of about 800°C to about 1200°C.

[0047] According to various embodiments, system 200 can include an optional air preheater located outside hot box 300 (not shown, or inside the hot box in FIG. 3A ). In particular, the air preheater can be configured to preheat the air supplied to hot box 300 by air blower 118. The primary purpose of the air preheater is as a cooler for the cathode products. It cools the product H / residual steam to a lower temperature to reduce overall power consumption and to lower the temperature below the maximum temperature of the steam recycle blower (e.g., 180° C. or 200° C.). Although not shown, a steam recycle blower may be located adjacent to the flow leaving splitter 116 (e.g., immediately to the left of the side flow leaving splitter 116).

[0048] In some embodiments, the system 200 can be operated in a thermal neutral configuration, in which a thermal neutral voltage is provided to the stack 100. In particular, the current provided to the stack 100 is I 2 The heat generated by R heating can be varied to balance the (endothermic) heat of reaction, thus minimizing or eliminating the use of steam heater 110 and / or air heater 114 during steady-state thermoneutral operation.

[0049] The hydrogen stream exiting the steam recuperator 108 and optional hydrogen separator 116 at a temperature between 120°C and 150°C can be compressed and / or purified in the hydrotreater 120, which can include a high-temperature hydrogen pump operating at a temperature between about 120°C and about 150°C to remove about 70% to about 90% of the hydrogen from the hydrogen stream. The remaining unpumped effluent from the hydrogen pump is a water-rich stream that has already been fully vaporized. This water-rich stream can be fed to the mixer 106 or a blower for recycling to the steam recuperator 108, eliminating the need for water vaporization in the steam generator 104.

[0050] By increasing the hydrogen pump pressure, for example, to a pressure in the range of about 20-50 psig, steam loss into the hydrogen stream can be minimized. This separation can be done at the electrolyzer module level (e.g., a single hot box), at the system level (e.g., a group of hot boxes (e.g., a group of 3 or 4)), at the stamp level (e.g., a larger group that shares some joint components (e.g., a water source)), or at the site level (all at a given site).

[0051] Condensing the water and compressing the hydrogen stream can consume a significant amount of power. In some embodiments, the air flow to the stack 100 can be reduced or stopped so that the stack 100 outputs pure or nearly pure oxygen gas as the stack exhaust. Additionally, the air and fuel sides of the electrolysis cell 1 can be operated at equal pressures ranging from about 3 psig to about 50 psig. In some embodiments, the air supplied to the stack 100 can be supplied at a minimal flow rate to avoid significant power consumption by an upstream air compressor.

[0052] High pressure operation allows for the elimination of power and equipment associated with the first stage of hydrogen flow compression, can reduce the size of the first condenser stage due to the higher dew point associated with higher pressure, and / or can reduce the physical space required for the flow channels due to the higher density associated with higher pressure.

[0053] According to various embodiments, system 200 may include a controller 122, such as a central processing unit, configured to control the operation of system 200. For example, controller 122 may be wired or wirelessly connected to and control various elements of system 200.

[0054] In some embodiments, the controller 122 can be configured to control the system 200 such that the system 200 can operate in a standby mode in which no hydrogen flow is produced. During the standby mode, the electric heater associated with (i.e., in heat transfer relationship with) the stack 100 can be operated at a minimum power level required to keep the electrolysis cell 1 at a desired standby temperature. The desired standby temperature may differ from the desired production operating temperature and may be affected by the allowable time required to return to the desired operating temperature.

[0055] Recovery from standby mode to steady-state operation may allow hydrogen production to begin at temperatures lower than the standard steady-state operating temperature. At lower temperatures, cell resistance may be higher, which may provide additional heating to bring the stack 100 up to steady-state operating temperature once the system begins to recover from hot standby. The water / steam supply during hot standby may be significantly reduced or eliminated. The addition of hydrogen to the steam in the mixer 106 may also be significantly reduced or eliminated.

[0056] In some embodiments, hydrogen separator 116 can be used to divert hydrogen flow so that hydrogen can be supplied to replace most or all of the steam in system 200 during hot standby. Separator (e.g., valve) 116 can then be closed to maintain a reducing atmosphere within stack 100 without further hydrogen consumption. Air flow to stack 100 can be significantly reduced or eliminated. In some embodiments, there can be a minimum air flow to prevent air heater 114 from overheating.

[0057] System 200 can include a hydrotreater 120 configured to process a hydrogen stream. For example, hydrotreater 120 can be configured to compress the hydrogen stream to a desired pressure, such as about 3000 to about 8000 psig. The compression can include multiple stages, possibly with cooling and water removal between stages.

[0058] During hot standby, the steam heater 110 can be operated at a minimum power level to prevent overheating in the absence of a water / steam supply. The hydrogen stream from stack 100 (i.e., the hydrogen exhaust stream) can be a warm stream containing hydrogen gas and water. The desired product can be high-pressure (e.g., about 500 to about 8000 psig) purified hydrogen. The hydrogen streams from multiple on-site stacks 100 can be combined into a single stream. This combined stream can be cooled as much as practical using, for example, an air cooler or heat exchanger cooled by an on-site cooling water tower, which can be part of the hydrotreater 120. The hydrogen exhaust from hydrotreater 120 can be stored, used (immediately or continuously), or offered for sale as a product.

[0059] In various embodiments, hydrotreater 120 can include at least one electrochemical hydrogen pump, liquid ring compressor, diaphragm compressor, other compression device, or combinations thereof. For example, hydrotreater 120 can include a series of electrochemical hydrogen pumps, which can be arranged in series and / or parallel with respect to the flow direction of the hydrogen stream, to compress the hydrogen stream. Electrochemical compression can be more electrically efficient than conventional compression. The final product from compression can still contain trace amounts of water. Therefore, hydrotreater 120 can optionally include a dehydration device, such as a temperature swing adsorption reactor or a pressure swing adsorption reactor, to remove this residual water. The system can be configured to repurify the residual water (e.g., in a DI bed) and provide the residual water removed from the compressed hydrogen stream to a water preheater.

[0060] The product may also contain traces of nitrogen gas, which may be from air dissolved in the water. Electrochemical compression can essentially remove traces of nitrogen.

[0061] In some embodiments, the condensed water may be recycled to the process feed (feed to the DI bed) in water source 50. The hydrogen added to the steam in mixer 106 may be produced during the first stage or any intermediate stage of the compression train and can be dehumidified as needed. Hydrogen storage device 52 may include a low / medium pressure storage tank for the hydrogen supplied to stack 100 through mixer 106.

[0062] According to various embodiments, the controller 122 may be configured to control the operation of the system 200 based on various site-wide control parameters. For example, the controller 122 may be configured to control the production of hydrogen based on any of the following: the operating limits of each SOEC stack; power availability; instantaneous average electricity cost, including the impact of demand charges at all tiers; instantaneous marginal electricity cost, including the impact of demand charges at all tiers; instantaneous renewable content; available hydrogen storage capacity; stored energy available for use (e.g., thermal or electrical storage); hydrogen production planning (e.g., daily, weekly, or monthly planning); impact on hydrogen production revenue (e.g., sales price, production level adjustments, shortfalls, etc.); maintenance schedule; the relative health of all hot boxes on-site; the mechanical condition of the compression / condensation trains; the availability of water / steam / hydrogen supplies; weather conditions and / or forecasts; other known external constraints, either instantaneous or during a production schedule (e.g., only so much water available per month, only so many megawatt-hours (MW-hr) available per month, etc.); and / or the minimum allowable time to begin producing hydrogen from standby mode (if standby is expected to last several hours, it may be desirable to cool the cells below normal operating temperature).

[0063] 3A is a schematic diagram illustrating the process flow in an alternative electrolyzer system 201, according to various embodiments of the present disclosure. Electrolyzer system 201 may be similar to electrolyzer system 200, so only the differences between them will be discussed in detail.

[0064] 3A , the electrolyzer system 201 can include an optional air preheater 328 located inside the hot box 300. Alternatively, the optional air preheater 328 can be located outside the hot box 300. The air preheater 328 can be a heat exchanger configured to utilize heat obtained from the hydrogen stream exiting the steam recuperator 108 to preheat the air supplied by the air blower 118. The preheated air can then be supplied to the air recuperator 112. In this embodiment, no additional electric or gas heater is required to provide heat to the air preheater 328. The optional air preheater 328 allows the hydrogen / steam stream to the hydrogen separator 116 to be substantially cooler, allowing the hydrogen separator to be made of less expensive materials.

[0065] In some embodiments, a small amount of liquid water (e.g., about 0.5% to about 2% of the incoming water) may be periodically or continuously discharged from the steam generator 104. In particular, the discharged liquid water may contain scale and / or other mineral impurities that may accumulate in the steam generator 104 during the vaporization of water to generate steam. Therefore, this discharged liquid water is undesirable for recirculation into the water inlet stream from the water source 50. This liquid effluent may be mixed with the hot oxygen exhaust stream discharged from the water preheater 102 to the exhaust conduit. The hot oxygen exhaust stream may be at a temperature greater than 100°C, e.g., 110-130°C, e.g., 120°C. Thus, the liquid water effluent may be vaporized by the hot oxygen exhaust stream such that the liquid water does not need to be discharged from the system 201. The system 201 optionally includes a pump 124 configured to pump and regulate the liquid water effluent discharged from the steam generator 104 into the oxygen exhaust discharged from the water preheater 102. Optionally, a proportional solenoid valve can be added in addition to the pump 124 to further regulate the flow of liquid water discharge.

[0066] 3B is a schematic diagram illustrating the process flow in another alternative electrolyzer system 203, according to various embodiments of the present disclosure. Electrolyzer system 203 may be similar to electrolyzer system 201, and therefore only the differences therebetween will be described in detail.

[0067] Referring to FIG. 3B , the electrolyzer system 203 may be configured to provide an improved water and / or steam supply. In particular, the power consumption of the electrolyzer system may depend on the water utilization of the electrolysis cells. In particular, it is believed that increasing water utilization will decrease the power consumption of the system. However, the inventors have discovered that the water preheater may generate steam in addition to the preheated water. As a result, the preheated water discharged from the water preheater may be separated into a water "slug" by the entrained steam. This may lead to uneven output rates of the mass flow of preheated water from the water preheater to the steam generator. Such unevenness reduces the uniformity of steam generation in the steam generator and the water utilization rate of the system, forcing a decrease in the water utilization rate and resulting in an increase in the power consumption of the overall system.

[0068] Thus, the system 203 can include various components to improve the uniformity of steam generation, thereby increasing water utilization and reducing system power consumption. For example, the system 203 can include an auxiliary steam generator 130 in addition to the separate steam generator 104, also referred to as the primary steam generator 104. The auxiliary steam generator 130 generates a portion of the steam supplied to the stack 100 using hot oxygen exhaust to reduce power consumption by the primary steam generator 104. To avoid temporary slagging in the water flow from the auxiliary steam generator 130, the steam may be superheated. Thus, the auxiliary steam generator 130 can also be referred to as a superheated steam generator. In one embodiment, the auxiliary steam generator 130, located within the hot box 300, is located between the air recuperator 112 and the water preheater 102 with respect to the flow direction of the oxygen exhaust from the electrolysis cell stack 100. In an alternative embodiment, the auxiliary steam generator 130 and / or the water preheater 102 can be located outside the hot box 300. In other embodiments, the water preheater 102 may be located upstream of the auxiliary steam generator 130 with respect to the flow direction of the oxygen exhaust.

[0069] In various embodiments, the system 203 may include a water conduit 132, such as a water manifold or pipe, configured to supply separate water flows from the water source 50 to the hot box 300. In particular, the water conduit 132 may be configured to supply a first water flow to the auxiliary steam generator 130 and a second water flow to the water preheater 102. For example, a first valve 134 may be disposed on the conduit 132 and configured to control the flow rate of water to the auxiliary steam generator 130 (i.e., the flow rate of the first water flow), and a second valve 136 may be disposed on the conduit 132 and configured to control the flow rate of water to the water preheater 102 (i.e., the flow rate of the second water flow). The first and second valves 134, 136 may be flow control valves, such as mass flow control valves, and may be operated under the control of the controller 122 or manually. In some embodiments, one of the first valve 134 and the second valve 136 may be omitted, and the flow of water may be controlled by a single valve, such as the first valve 134, in conjunction with controlling the flow rate from the water source 50. Alternatively, the first valve 134 and the second valve 136 may be combined into a single proportional three-way valve. In another alternative embodiment, a splitter may be provided in the water conduit 132 to divide the water in the water conduit 132 into first and second water flows.

[0070] The oxygen exhaust from the air recuperator 112 can pass through the auxiliary steam generator 130 and then through the water preheater 102. Thus, the water preheater 102 is disposed downstream of the auxiliary steam generator 130 with respect to the flow direction of the oxygen exhaust from the air recuperator 112. A first oxygen exhaust conduit 137A fluidly connects the oxygen exhaust outlet of the oxygen exhaust source (e.g., the oxygen exhaust outlet of the air recuperator 112) to the oxygen exhaust inlet of the auxiliary steam generator 130. A second oxygen exhaust conduit 137B fluidly connects the oxygen exhaust outlet of the auxiliary steam generator 130 to the oxygen exhaust inlet of the water preheater 102.

[0071] The auxiliary steam generator 130 may be configured to generate steam by heating a first water stream using heat obtained from the oxygen exhaust discharged from the air recuperator 112. For example, the oxygen exhaust discharged from the air recuperator 112 may be in a range of about 200°C to about 350°C, e.g., about 250°C to about 300°C. Thus, the auxiliary steam generator 130 may generate steam having a temperature in a range of about 120°C to about 160°C, such as, for example, about 130°C to about 150°C. The system 203 may be configured to supply steam generated by the auxiliary steam generator 130 to the mixer 106, which may be located outside the hot box 300.

[0072] The water preheater 102 can be configured to preheat the second water stream to a temperature of less than about 98°C or less than about 95°C, for example, to a temperature in a range of about 95°C to about 60°C, using heat obtained from the oxygen exhaust gas discharged from the auxiliary steam generator 130. For example, the oxygen exhaust gas discharged from the auxiliary steam generator 130 to the water preheater 102 can have a temperature in a range of about 125°C to about 200°C, such as about 135°C to about 165°C, or about 150°C. Accordingly, the preheated water discharged from the water preheater 102 can have a temperature in a range of about 75°C to about 98°C, such as about 85°C to about 97°C, or about 90°C to about 95°C. In other words, because the water is preheated using the oxygen exhaust gas cooled by the air recuperator 112 and the auxiliary steam generator 130, steam generation in the water preheater 102 can be substantially reduced and / or prevented. In other words, the oxygen exhaust may be supplied to the water preheater 102 at a lower temperature than the temperature at which it is supplied to the auxiliary steam generator 130. This may reduce or prevent steam generation in the water preheater 102. This may also reduce or prevent the formation of a "slug" of water exhausted from the water preheater to the primary steam generator 102.

[0073] In various embodiments, system 203 may include a flow restrictor 138 disposed on a steam conduit 140 configured to supply steam from primary steam generator 104 to mixer 106. Steam conduit 140 fluidly connects a steam outlet of primary steam generator 104 to mixer 106. Auxiliary (i.e., superheated) steam conduit 141 fluidly connects a steam outlet of auxiliary steam generator 130 to mixer 106. In particular, flow restrictor 138 is configured to increase backpressure within primary steam generator 104 via steam conduit 140. Flow restrictor 138 may include an opening (e.g., an orifice) or conduit having an inner diameter smaller than the inner diameter of steam conduit 140. For example, flow restrictor 138 may be a portion of steam conduit 140 that has a smaller inner diameter than the remainder of steam conduit 140. In other embodiments, flow restrictor 138 may be a relatively small diameter conduit fluidly connected to steam conduit 140 or may be a relatively small diameter conduit inserted inside steam conduit 140. In other embodiments, flow restrictor 138 may be a plate incorporated into the outlet of primary steam generator 104 with relatively small diameter openings through which steam flows before entering steam conduit 140.

[0074] The flow restrictor 138 may increase the back pressure in the primary steam generator 104. The flow restrictor 138 may also induce a pressure drop in the steam conduit 140 (which may superheat the steam flowing therethrough) to ensure that the steam is discharged from the primary steam generator 104 at a desired temperature and consistent flow rate. Additionally, the flow restrictor 138 may reduce liquid entrainment and / or liquid water slug formation in the steam conduit 140.

[0075] In some embodiments, the system 203 can be configured to control the temperature of the oxygen exhaust by controlling the airflow through the system 203. For example, the controller 122 can be configured to control the air blower 118 to increase or decrease the airflow to the stack 100, thereby increasing or decreasing the flow rate of the oxygen exhaust. In particular, a higher air flow rate to the stack 100 can increase the enthalpy flow of the oxygen exhaust, and a lower air flow rate can decrease the enthalpy flow of the oxygen exhaust. Controlling the oxygen exhaust temperature can provide increased flexibility in achieving desired temperatures for the steam exhausted from the auxiliary steam generator 130 and / or the preheated water exhausted from the water preheater 102.

[0076] In various embodiments, a method of operating system 203 can include generating steam by vaporizing water supplied to auxiliary steam generator 130 using heat obtained from the oxygen exhaust supplied from air recuperator 112 to the auxiliary steam generator, generating preheated water by heating water supplied to water preheater 102 using heat obtained from the oxygen exhaust supplied from auxiliary steam generator 130, generating steam by vaporizing the preheated water in primary steam generator 104, and generating hydrogen exhaust and oxygen exhaust using stack 100 using steam generated by primary steam generator 104 and auxiliary steam generator 130. In one embodiment, the method can also include increasing system backpressure using flow restrictor 138.

[0077] In particular, steam generated by the primary steam generator 104 and the auxiliary steam generator 130 may be supplied to a mixer 106 to form a steam mixture. The steam mixture may be supplied to a steam heater 110 and a steam recuperator 108 before being supplied to the stack 100. The oxygen exhaust supplied to the steam generator 130 may have a higher temperature than the oxygen exhaust supplied to the water preheater 102.

[0078] 3C is a schematic diagram illustrating the process flow in another alternative electrolyzer system 205, according to various embodiments of the present disclosure. Electrolyzer system 205 may be similar to electrolyzer system 203, and only the differences therebetween will be described in detail.

[0079] 3C , the water preheater 102 and the auxiliary steam generator 130 may be fluidly connected in parallel to a source of oxygen exhaust, such as the outlet of the air recuperator 112. For example, the system 205 may include a valve or splitter 135 disposed on the first oxygen exhaust conduit 137A, and a second oxygen exhaust conduit 137B may fluidly connect the valve or splitter 135 to the water preheater 102. The valve or splitter 135 may be configured to divert a portion of the oxygen exhaust to the second oxygen exhaust conduit 137B, such that the water preheater 102 is supplied with oxygen exhaust that does not pass through the auxiliary steam generator 130.

[0080] In system 205 , steam heater 110 may also be located downstream of steam recuperator 108 with respect to the flow direction of the steam / hydrogen mixture from mixer 106 to stack 100 .

[0081] 3D is a schematic diagram illustrating the process flow in another alternative electrolyzer system 207, according to various embodiments of the present disclosure. Electrolyzer system 207 may be similar to electrolyzer system 205, and only the differences therebetween will be described in detail.

[0082] 3D , system 207 can include a combined heat exchanger 131 including an auxiliary steam generator and a water preheater. The combined heat exchanger 131 can receive separate water streams from a water conduit 132 and output preheated water and auxiliary steam. The combined heat exchanger 131 can include separate conduits for water preheating and steam generation and a single oxygen exhaust chamber through which oxygen exhaust flows. The separate preheat and steam conduits can be configured to obtain heat from the oxygen exhaust flowing through the oxygen exhaust chamber. Thus, system 207 can omit the second oxygen exhaust conduit 137B included in system 205.

[0083] Figure 4A is a perspective view of a hot box 300, and Figure 4B is a perspective view of the hot box 300 with the outer shell removed, according to various embodiments of the present disclosure. With reference to Figures 4A and 4B, the hot box 300 can include an outer shell 302 and an inner shell 304 disposed on a base plate 306. The inner shell 304 can include an upper inner shell 304A and a lower inner shell 304B.

[0084] A cover plate 310 may be disposed above the outer shell 302 and the inner shell 304. The base plate 306 may be disposed on a support frame 308. The support frame 308 may include hollow rails that a forklift can access to raise and move the hot box 300. A water inlet conduit 312, a preheated water outlet conduit 314, and an air (e.g., oxygen-enriched air) outlet conduit 316 may extend through the cover plate 310. A central column 320 may also extend through the cover plate 310. The air inlet conduit 322, the preheated water (e.g., steam) inlet conduit 324, and the hydrogen outlet conduit 326 may be disposed on the central column 320.

[0085] The air recuperator 112 may be located in the upper portion of the hot box 300, and the air heater 114 may be located in the lower portion of the hot box 300. In particular, the outer shell 302 and the upper inner shell 304A may form at least a portion of the air recuperator 112. The air heater 114 may include one or more peripheral heating elements 214 disposed between the lower inner shell 304B and the outer shell 302. The peripheral heating elements 214 may include resistive heating elements powered by an external current or voltage. The peripheral heating elements 214 may extend laterally in a serpentine pattern. However, any suitable coil pattern or configuration may be used. The peripheral heating elements 214 may be held in place by support elements 220. The support elements 220 may be configured to maintain the spacing between the inner shell 304 and the outer shell 302. In some embodiments, the support elements 220 may include brackets formed of a dielectric material capable of withstanding high temperatures, such as a ceramic material.

[0086] 5A is a cross-sectional view of hot box 300 of FIGS. 4A and 4B in accordance with various embodiments of the present disclosure, and FIG. 5B is a cross-sectional view of hot box 300 showing components located inside central column 320. FIG. 5C is a partial perspective view showing elements of steam recuperator 108 and / or air recuperator 112 of hot box 300, and FIG. 5D is a perspective view showing distribution hub 340 of hot box 300.

[0087] 5A and 5B, a hot box 300 can include electrolysis cell stacks 100 arranged in multiple columns around a central column 320. An air recuperator 112 can surround the top of the stack 100. The air recuperator 112 can include an outer chamber 112C1 and an inner chamber 112C2 separated by a separator plate (not shown).

[0088] The air heater 114 may include a peripheral heating element 214 and, optionally, one or more central heating elements 216 and one or more bottom heating elements 218. The heating elements 214, 216, 218 may be, for example, electrical resistance elements or induction heating elements, such as AC or DC heating coils. The peripheral heating element 214 may surround the bottom of the stack 110. The central heating element 216 may surround the central column 320 and may be surrounded by the stack 100. The central heating element 216 may operate to maintain the temperature of the central column 320. The bottom heating element 218 may be disposed below the stack 100.

[0089] In various embodiments, the peripheral heating element 214 can be covered by the insulating layer 318. For example, the peripheral heating element 214 can be disposed in the space between the lower inner shell 304B and the insulating layer 318, or within the insulating layer 318.

[0090] The water preheater 102 may be disposed above the stack 100. In particular, the water preheater 102 may include a coiled water pipe 103 disposed on a cover plate 310. The inlet of the coiled water pipe 103 is fluidly connected to a water inlet conduit 312. The outlet of the coiled water pipe 103 is fluidly connected to a preheated water outlet conduit 314. The preheated water outlet conduit 314 may be fluidly connected to a preheated water inlet conduit 324 in the central water column by extending upward and then inward from the coiled water pipe 103. The air outlet conduit 316 may be disposed above the water preheater 102 such that oxygen (i.e., oxygen-enriched air) exhaust air flows past the coiled water pipe 103 of the water preheater 102 before exiting the hot box 300.

[0091] The steam generator 104 may be disposed within an upper portion of the central column 320. The steam heater 110 may be disposed within a lower portion of the central column 320. In particular, the steam heater 110 may be fluidly connected to the steam generator by a connecting conduit 330.

[0092] The steam generator 104 may include a vaporizer manifold 104M and at least one heating element 104E disposed within or adjacent to the vaporizer manifold 104M. The vaporizer manifold 104M may connect the preheated water inlet conduit 324 to a connecting conduit 330. The heating element 104E may be configured to generate steam by vaporizing water flowing within the conduits of the vaporizer manifold 104M. In some embodiments, the vaporizer manifold 104M may include conduits disposed on the exterior and interior of the heating element 104E such that heat can be obtained from the interior and exterior of the heating element 104E and used to vaporize the water flowing through the vaporizer manifold 104M.

[0093] 5B, steam heater 110 can include a housing 110H having at least one heating element 110E and a steam manifold 110M disposed therein. Steam manifold 110M can surround heating element 110E and be fluidly connected to connecting conduit 330. In some embodiments, steam heater 110 can be configured to superheat steam generated by steam generator 104. In some embodiments, steam manifold 110M can include conduits disposed on the exterior and interior of heating element 110E such that heat can be obtained from the interior and exterior of heating element 110E and used to superheat steam flowing through steam manifold 110M.

[0094] The heating elements 104E, 110E may be electric heating elements as described above. In some embodiments, the heating elements 104E, 110E may be heating coils. In some embodiments, the heating elements 104E, 110E may be physically isolated from the water and / or steam flowing past them to prevent direct contact with the water and / or steam.

[0095] The steam recuperator 108 may be located in the central column 320 and surround the steam heater 110. The steam recuperator 108 is located upstream from the steam heater 110, as shown in Figure 2A.

[0096] In some embodiments, an optional air preheat heat exchanger 328 may be located in the central column 320 and surround the steam generator 104. The air preheat heat exchanger 328 includes at least one air inlet conduit and at least one hydrogen outlet conduit such that the hydrogen outlet stream preheats the air inlet stream.

[0097] As shown in FIG. 5C , steam recuperator 108 and / or air recuperator 112 can include separator plates 108P, 112P, respectively. In some embodiments, separator plates 108P, 112P can be corrugated. Separator plate 108P can be configured to divide steam recuperator 108 into outer chamber 108C1 and inner chamber 108C2. Separator plate 112P can be configured to divide air recuperator 112 into outer chamber 112C1 and inner chamber 112C2. In various embodiments, air preheater 328 can have a similar configuration, with the outer and inner chambers separated by corrugated separator plate 328P shown in FIG. 5A .

[0098] The outer chamber 108C1 of the steam recuperator 108 may be configured to receive hydrogen exhausted from the stack 100, and the inner chamber 108C2 may be configured to receive steam from the steam heater 110. However, in other embodiments, the outer chamber 108C1 may receive steam and the inner chamber 108C2 may receive hydrogen.

[0099] The outer chamber 112C1 of the air recuperator 112 may be configured to receive air from the central column 320, and the inner chamber 112C2 may be configured to receive oxygen exhaust from the stack 100. However, in other embodiments, the outer chamber 112C1 may receive oxygen exhaust and the inner chamber 112C2 may receive air.

[0100] As shown in FIG. 5D , the central column 320 can be disposed on a distribution hub 340. The distribution hub 340 can be configured to fluidly connect the central column 320 to the stacks 100 disposed thereon. Although only two stacks 100 are shown in FIG. 5D , the distribution hub 340 can be fluidly connected to all of the stacks included in the hot box 300. The distribution hub 340 can include a steam distribution conduit 340S and a hydrogen collection conduit 340H. The steam distribution conduit 340S can be configured to distribute steam from the central column 320 to the stacks 100, and the hydrogen collection conduit 340H can be configured to supply hydrogen produced by the stacks 110 to the central column 320.

[0101] 5A-5D , during operation, water may be supplied to the hot box 300 through the water inlet conduit 312. The water from the water inlet conduit 312 may then be circulated through the coiled water pipe 103 of the water preheater 102 such that the oxygen exhaust (i.e., oxygen-enriched air exhaust) flowing past the coiled water pipe 103 preheats the water flowing through the coiled water pipe 103. The preheated water may then be supplied from the coiled water pipe 103 of the water preheater 102 surrounding the central column 320 through the preheated water outlet conduit 314 to the preheated water inlet conduit 324 within the central column 320.

[0102] The preheated water may then flow downward through the central column 320. In particular, the preheated water may flow from the preheated water inlet conduit 324 into the vaporization manifold 104M of the water vaporizer 104. Heat generated by the heating element 104E may be used to vaporize the preheated water in the vaporization manifold 104M to generate steam.

[0103] Steam may be supplied to steam heater 110 from vaporizer manifold 104M through connecting conduit 330. In particular, steam may pass through steam manifold 110M while being superheated by heating element 110E. Steam may exit steam manifold 110M at the bottom of housing 110H. The steam may then flow upward into steam recuperator 108, which surrounds the steam heater.

[0104] The steam may flow downward through the inner chamber 108C2 of the steam recuperator 108 before being supplied to the distribution hub 340. The steam may flow through steam distribution conduits 340S to each of the stacks 100 (e.g., to each column of the stack 100). The steam may then be supplied to the fuel (e.g., cathode) electrodes of the SOECs of the stack 100. Hydrogen vapor generated by the stack 100 (e.g., at the fuel electrodes of the SOECs of the stack 100) may be supplied to the hydrogen collection conduit 340C so that the distribution hub 340 provides a combined hydrogen stream to the central column 320. The hydrogen stream may include unreacted steam exhausted from the stack 100. An oxygen exhaust (i.e., oxygen-enriched air) stream may be supplied from the air (i.e., anode) electrodes of the SOECs of the stack 100 to the air recuperator 112 surrounding the stack 100 columns.

[0105] In some embodiments, hot box 300 may include riser conduits 332 (see also FIG. 11 ) that fluidly connect stacks 100 to steam distribution conduits 340S and hydrogen collection conduits 340C. In particular, riser conduits 332 may include steam conduits for supplying steam to the SOECs of each stack 100 and hydrogen conduits configured to collect hydrogen exhausted by the SOECs of each stack 100. Thus, stacks 100 may be internally manifolded for steam / hydrogen and externally manifolded for oxygen / air.

[0106] The distribution hub 340 can supply the hydrogen stream to the steam recuperator 108, where it can flow upward through the outer chamber 108C1. The hydrogen stream can heat the steam flowing downward through the inner chamber 108C2. The hydrogen stream can exit the steam recuperator 108 and flow up the central column 320 to the air preheater 328. In particular, the hydrogen stream can flow through a first chamber of the air preheater 328 to the hydrogen outlet conduit 326, heating the air inlet stream that flows through a second chamber of the air preheater 328, which is separated from the first chamber by a plate 328P.

[0107] Air may be supplied to the hot box 300 through an air inlet conduit 322. The air may be supplied to a first chamber of an air preheater 328, where it may be preheated by a flow of hydrogen in a second chamber. From the air preheater 328, the heated air may flow through the coils of the water preheater 102 and into the air recuperator 112.

[0108] In particular, air may flow downward through the outer chamber 112C1 of the air recuperator 112 to the air heater 114. The air may be heated as it flows down the hot box 300 through the peripheral heating elements 214, across the bottom of the hot box 300 through the optional bottom heating element 218, and up the central column 320 through the central heating element 216. The heated air may then exit the air heater 114 (e.g., through openings in the top and / or side of the central heating element 216) and flow to the stack 110. The temperature of the air may be adjusted by adjusting the power applied to one or more of the heating elements 214, 216, 218. Air may be provided radially outward from the central plenum 320 to the air (i.e., anode) electrodes of the externally manifolded SOECs of the stack 100. At the air electrode, air combines with oxygen (i.e., oxide) ions diffusing from the fuel (i.e., cathode) side of the SOEC through the SOEC electrolyte. The air and oxygen mixture produced at the air electrode of the SOEC can be supplied from the air (i.e., anode) electrode of the SOEC in stack 100 as an oxygen exhaust (i.e., oxygen-enriched air) stream radially outward from the stack 100 column.

[0109] The oxygen exhaust may flow radially outward from the stack 100 and enter the inner chamber 112C2 of the air recuperator 112. The air recuperator 112 may utilize heat obtained from the oxygen exhaust stream in the inner chamber 112C2 to heat the air (i.e., air inlet) stream in the outer chamber 112C1. The oxygen exhaust stream may then flow through the coiled water pipe 103 of the water preheater 102 before exiting the hot box 300 via the air outlet conduit 316. The oxygen exhaust stream flowing through the water preheater 102 may also further preheat the air stream flowing through a shoulder manifold 334 that fluidly connects the air preheater 328 and the air recuperator 112 and extends adjacent to the water preheater 102.

[0110] FIG. 6 is a cross-sectional perspective view of a central column 320 including a modified steam generator 404 according to an alternative embodiment of the present disclosure. The steam generator 404 can be used in place of the steam generator 104 described above. Referring to FIG. 6, the steam generator 404 can be disposed inside the central column 320. In particular, the steam generator 404 can be surrounded by an air preheater 328. The steam generator 404 can include a heating element 404E and a vaporization conduit 404C disposed inside the superheating element 404E. The heating element 404E can be a resistive heating element or a coil, as described above. In this embodiment, the external preheated water outlet conduit 314 shown in FIGS. 5A and 5B can be replaced by an internal preheated water outlet conduit 314A located inside the central plenum 320.

[0111] During operation, preheated water may be supplied from the water preheater 102 to an internal preheated water outlet conduit 314A located between the air preheater 328 and the vaporization conduit 404C. The water may flow up through the internal preheated water outlet conduit 314A before entering the vaporization conduit 404C through the preheated water inlet conduit 324.

[0112] The voltage applied to the heating element 404E results in resistive heating of the heating element 404E. The heat is then transferred to the water in the vaporization conduit 404C, resulting in the generation of water vapor, e.g., steam. Over time, a small amount of scale may accumulate at the bottom of the steam generator 404 due to contaminants present in the water. Such scale may reduce heat transfer. Therefore, as shown in FIG. 3A, a small amount of preheated water may be drained from the bottom of the steam generator 404 to remove scale and / or other contaminants.

[0113] FIG. 7A is a cross-sectional perspective view of central column 320 and external steam generator 504 according to another alternative embodiment of the present disclosure, and FIG. 7B is an enlarged partial cross-sectional view of steam generator 504 of FIG. 7A. Steam generator 504 can be used in place of steam generators 104, 404 described above. With reference to FIGS. 7A and 7B, steam generator 504 can be located outside central column 320. In some embodiments, steam generator 504 can be located outside hot box 300 and / or mounted externally to the hot box. An outlet of steam generator 504 can be fluidly connected to central column 320 by an insulated steam conduit 408 surrounded by insulation 409.

[0114] 7B, the steam generator 504 may include an internal heating surface 504H, such as a resistive heating element. An inlet 504I of the steam generator 504 may be fluidly connected to the water preheater 102, and an outlet 504O of the steam generator 504 may be fluidly connected to the conduit 330. The steam generator 504 may include a helical baffle 504B disposed inside the outer tube 504T to define a steam flow path 504P.

[0115] As shown in FIG. 7C , the steam generator 504 also includes one or more exhaust ports 504D through which condensed liquid may be discharged from the steam generator 504 to prevent scale buildup in the steam generator 504. The exhaust ports 504D may be fluidly connected to the air outlet conduit 316 (see FIGS. 3, 5A, and 5B ) so that the liquid exhaust is evaporated and carried away in the oxygen exhaust exhaust from the hot box. The drain port 504D may include a valve 506 that can be opened to drain water. The drain port 504D may include the same conduit as the inlet 504I or a different conduit. Locating the steam generator 504 external reduces difficulties in routing wiring, drainage, and piping for the steam generator 504.

[0116] In alternative embodiments, the steam generator 104 may include an immersed steam generator 604, an in-line steam generator 704, or a multi-heater steam generator array 804, as shown in Figures 7D, 7E, and 7F, respectively. Alternatively, a stand-alone steam generator may be used as the vaporizer for the SOEC hot box 300.

[0117] FIG. 8A is a partially transparent perspective view of a portion of the air heater 114 including a peripheral heating element 214 having an alternative structure, according to various embodiments of the present disclosure. Referring to FIG. 8A , the peripheral heating element 214 may have an open coil configuration and may extend laterally. In particular, the peripheral heating element 214 may be annular and stacked vertically parallel to the stacking direction of the electrolysis cells in the stack 100. The peripheral heating element 214 may be secured to a support element 220 disposed between the inner and outer shells 304 and 302 of the hot box. In some embodiments, the support element 220 may be a bracket formed of a dielectric material, such as a ceramic material. The outer shell 302 may be covered by a thermal insulation layer 318.

[0118] 8B is a cross-sectional perspective view of a portion of the air heater 114 including a peripheral heating element 214 and a support element 222 having an alternative configuration, according to various embodiments of the present disclosure. Referring to FIG. 8B, the peripheral heating element 214 may be a coil-shaped heating element extending vertically in the space between the inner shell 304 and the outer shell 302. The peripheral heating element 214 may be disposed within a vertically extending tubular support element 222. In some embodiments, the support element 222 may comprise a heat-resistant dielectric material, such as a ceramic material. The support element 222 may be configured to electrically insulate the peripheral heating element 214 from the inner shell 304 and the outer shell 302. The peripheral heating elements 214 may be electrically connected, for example, in series or in parallel.

[0119] FIG. 8C is a perspective view of a portion of an air heater 114 including a peripheral heating element 214 having an alternative configuration, and FIG. 8D is a cross-sectional perspective view of the air heater 114 of FIG. 8C . Referring to FIGS. 8C and 8D , an insulating layer 318 can be disposed between the inner shell 304 and the outer shell 302. In some embodiments, the insulating layer 318 can be formed of a dielectric, heat-resistant material, such as a ceramic material. The peripheral heating element 214 can extend laterally and can be embedded in the insulating layer 318. Thus, the insulating layer 318 can electrically insulate the peripheral heating element 214.

[0120] 8E is a perspective view of a portion of an air heater 114 including a peripheral heating element 214 having an alternative configuration, according to various embodiments of the present disclosure. Referring to FIG. 8E, the peripheral heating element 214 is cylindrical and can be stacked vertically. The peripheral heating element 214 can include fins 224 to improve heat dissipation. This type of heater configuration can be easier to assemble, as it can be manipulated in situ and manually inserted around the inner shell 304.

[0121] FIG. 8F is a perspective view of a portion of an air heater 114 including a peripheral heating element 214 having an alternative configuration, according to various embodiments of the present disclosure. Referring to FIG. 8F, the peripheral heating element 214 can be arranged on the inner shell 304 in a serpentine pattern. For example, the peripheral heating element 214 can be clamped to the inner shell 304 using support elements 220. The air heater 114 can include guide vanes 226 configured to guide incoming air along the peripheral heating element 214. The guide vanes 226 can include a flat upper surface angled at an angle of 10 to 80 degrees, e.g., 30 to 60 degrees, relative to the vertical airflow direction to impart a radial flow to the air beneath the guide vanes 226. The peripheral heating element 214 can include a metal heating core encased in electrical insulation. Brazing tubes 228 can be brazed to the ends of the heating element 214 core to provide support and electrical insulation. The brazing tube 228 may be welded to a top-hat shaped structure 230 .

[0122] 8A-8F can be applied to the peripheral heating element 214, the central heating element 216, and / or the bottom heating element 218. For example, the central heating element 216 can have a coiled configuration, extend laterally or vertically, have fins, and / or be disposed on a support element such as a ceramic tube or ceramic spacer. In some embodiments, the central heating element 216 can be clamped to the central column 320 by a support element 220, as shown below with respect to FIGS. 9A and 9B.

[0123] Figure 9A is a schematic diagram illustrating an air heater 114 having a zone configuration according to various embodiments of the present disclosure. Figure 9B is a perspective view illustrating the heating elements of the air heater 114 of Figure 9A. With reference to Figures 9A and 9B, the air heater can include a peripheral heating element 214 and a center heating element 216. Although not shown, the air heater 114 can also include a bottom heating element.

[0124] The peripheral heating element 214 may be arranged in two or more zones, such as a first zone 214A and a second zone 214B. The first zone 214A may be arranged above and upstream of the second zone 214B with respect to the direction of air flow through the air heater 114. The central heating element 216 may be arranged in two or more zones, such as a third zone 216A, a fourth zone 216B, and a fifth zone 216C. The third zone 216A may be arranged below and upstream of the fourth zone 216B with respect to the direction of air flow, and the fourth zone 216B may be arranged below and upstream of the fifth zone 216C.

[0125] The air heater 114 may include at least one power supply 240 configured to independently control the voltage and / or current applied to the peripheral heating elements 214 in each of the zones 214A, 214B, 216A, 216B, and 216C. For example, the air heater 114 may include separate power supplies 240 for supplying power to each of the zones 214A, 214B, 216A, 216B, and 216C, respectively, or a single power supply configured to independently control the power supplied to each of the zones 214A, 214B, 216A, 216B, and 216C. The heat output of the peripheral heating elements 214 in each of the zones 214A, 214B, 216A, 216B, and 216C may be selectively controlled so that the air flowing through the air heater 114 has a temperature in a range of about 800°C to about 950°C, e.g., about 825°C to about 875°C, or about 850°C. In particular, the power supplied to the heating elements in each zone 214A, 214B, 216A, 216B, 216C can be independently controlled to provide thermal uniformity to the air flowing through the air heater 114.

[0126] Figure 10A is a cross-sectional view of a central column 320 including a modified steam heating element 110E according to various embodiments of the present disclosure, and Figure 10B is an enlarged portion of Figure 10A. With reference to Figures 10A and 10B, the heating element 110E may be a vertical loop heating coil disposed inside the central column 320. The heating element 110E may include a metal heating core encased in insulation.

[0127] The heating element 110E can be brazed to a brazing tube 210 that includes a weld flange. The weld flange can be welded to the hot box base plate 306 so that the end of the heating element 110E can be positioned below the central column 320. Thus, the exposed terminals of the heating element 110E can be protected from steam exposure, thereby increasing the reliability and cycle life of the heating element 110E.

[0128] During operation, steam from connecting conduit 330 may flow downward through steam recuperator 108 before exiting the bottom of steam recuperator 108 and flowing upward along housing 110H of steam heater 110. In this embodiment, as shown in FIG. 2A , steam recuperator 108 is located upstream of steam heater 110. The steam may then flow upward to the top of housing 110H before entering housing 110H and flowing downward while being heated by steam heating element 110E. The superheated steam may then exit the bottom of steam heater 110 and flow into steam distribution conduit 340S, which may supply superheated steam to the corresponding stack 100.

[0129] 11 is a cross-sectional perspective view showing the airflow through a modified hot box 300A according to various embodiments of the present disclosure. Hot box 300A may be similar to hot box 300, so only the differences between them will be described in detail.

[0130] 11 , air (i.e., the air inlet flow) may enter the hot box 300A through an air inlet conduit 322 and flow through an air preheater 328 and a shoulder manifold 334 before entering the inner chamber of the air recuperator 112. Air exiting the bottom of the air recuperator 112 may flow radially inward into the stack 100. Ceramic side baffles 342 located on the sidewalls of the SOEC stack 100 column maintain the flow of air from the air recuperator 112 to the stack 100.

[0131] The oxygen exhaust exiting the stack 100 may flow radially inward and then along the outer surface of the steam heater 110, where the oxygen exhaust (i.e., the oxygen-enriched air stream) is optionally heated by the central heating element 216 of the air heater 114. Alternatively, the central heating element 216 may be omitted. The heated oxygen exhaust then flows under the stack 100 around the distribution hub 340 and enters the air heater 114. The oxygen exhaust flowing through the air heater 114 may be heated by the peripheral heating element 214. The heated oxygen exhaust enters the outer chamber of the air recuperator 112 and may heat the air entering the inner chamber of the air recuperator 112. The oxygen exhaust may then flow through the water preheater 102, where it may preheat the water flowing through the coiled water pipe 103 and the air flowing through the shoulder manifold 334, before being discharged through the air outlet conduit 316.

[0132] 12 is a cross-sectional perspective view showing the airflow through a modified hot box 300B according to various embodiments of the present disclosure. Hot box 300B may be similar to hot box 300, so only the differences between them will be described in detail.

[0133] Referring to FIG. 12 , air can enter the hot box 300B through an air inlet conduit 322, flow through an optional air preheater 328, and then enter an internal air recuperator 112 disposed around the periphery of the central column 320. For example, the internal air recuperator 112 can surround the steam heater 110. The internal air recuperator 112 can include inner and outer chambers 112C1 and 112C2, as shown in FIG. 5C , through which air and oxygen exhaust flow. In particular, the internal air recuperator 112 can be configured to heat the air supplied to the central column 320 by obtaining heat from the oxygen exhaust exhausted from the stack 100. The air can also be heated by excess heat generated by the steam heater 110. The air can exit the air recuperator 112, flow radially outward around a distribution hub 340 beneath the stack 100, and then flow upward into the air heater 114. The air may be heated by peripheral heating elements 214 before exiting the air heater 114 and flowing radially inward into the stack 100 .

[0134] The oxygen exhaust exiting stack 100 may flow radially inward into the outer chamber of air recuperator 112 to heat the air entering the inner chamber of air recuperator 112. The oxygen exhaust may then flow upward, radially outward through water preheater 102, and then be exhausted from hot box 300B through air outlet conduit 316.

[0135] 11 and 12, the disclosed hot box configuration allows the incoming air to be heated by the oxygen exhaust. This allows the central heating element 216 to be omitted from the air heater 114. Thus, the air heater 114 can include only the peripheral heating elements 214 and can be serviced without entering the hot boxes 300A, 300B. The flow of water and steam through the hot boxes 300A, 300B can be the same as that described with respect to the hot box 300.

[0136] The previous 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 general principles defined herein may be applied to other aspects without departing from the scope of the present 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.

Claims

1. A central column configured to receive air and steam; a stack of solid oxide electrolysis cells surrounding the central column and configured to receive steam and air discharged from the central column and to discharge a hydrogen exhaust and an oxygen exhaust; a water preheater configured to preheat water using heat obtained from the oxygen exhaust; a primary steam generator configured to generate steam provided to the central column by vaporizing the water preheated by the water preheater; and 1. An electrolyzer system comprising: an electric air heater configured to heat air supplied from the central column to the stack, the electric air heater comprising a central heating element disposed on an outer surface of the central column and a peripheral heating element surrounding the stack.

2. an auxiliary steam generator configured to generate steam supplied to the stack by vaporizing water using heat obtained from the oxygen exhaust; a first oxygen exhaust conduit fluidly connecting an oxygen exhaust outlet of an oxygen exhaust source to an oxygen exhaust inlet of the auxiliary steam generator; and 10. The electrolyzer system of claim 1, further comprising a second oxygen exhaust conduit fluidly connecting an oxygen exhaust outlet of the auxiliary steam generator to an oxygen exhaust inlet of the water preheater.

3. 3. The electrolyzer system according to claim 2, wherein the water preheater is disposed downstream of the auxiliary steam generator in a flow direction of the oxygen exhaust gas such that the oxygen exhaust gas supplied to the water preheater has a lower temperature than the temperature of the oxygen exhaust gas supplied to the auxiliary steam generator.

4. the oxygen exhaust source includes a heat exchange air recuperator configured to obtain heat from the oxygen exhaust to preheat air supplied to the stack; 3. The electrolyzer system of claim 2, wherein the auxiliary steam generator is configured to receive the oxygen exhaust discharged from the air recuperator via the first oxygen exhaust conduit.

5. water conduits fluidly connecting a water source to the auxiliary steam generator and the water preheater, respectively; and 3. The electrolyzer system of claim 2, further comprising a first valve on the water conduit configured to control the flow of water through the water conduit to the auxiliary steam generator.

6. 6. The electrolyzer system of claim 5, further comprising a second valve on the water conduit configured to control the flow of water through the water conduit to the water preheater.

7. 3. The electrolyzer system of claim 2, further comprising a flow restrictor configured to increase backpressure in the primary steam generator.

8. 3. The electrolyzer system of claim 2, further comprising a combined heat exchanger, wherein the auxiliary steam generator and the water preheater are disposed within the combined heat exchanger, the combined heat exchanger including an oxygen exhaust chamber and separate conduits configured to generate the preheated water and auxiliary steam by obtaining heat from oxygen exhaust flowing through the oxygen exhaust chamber.

9. a mixer fluidly connected to the primary steam generator and the auxiliary steam generator and configured to receive the steam generated by the primary steam generator and the steam generated by the auxiliary steam generator; and 3. The electrolyzer system of claim 2, further comprising a steam heater fluidly connected to the mixer and configured to superheat steam exiting the mixer and supply the superheated steam to the stack or to a steam recuperator fluidly connected to the stack.

10. An air blower configured to supply air to the stack through the central column; and 10. The electrolyzer system of claim 9, further comprising a controller configured to control the air blower to control the enthalpy flow of the oxygen exhaust.

11. a mixer configured to receive the steam from the primary steam generator and the steam from the auxiliary steam generator and to output a steam mixture; a steam recuperator configured to utilize heat obtained from the hydrogen exhaust to heat the steam mixture; and 3. The electrolyzer system of claim 2, further comprising a steam heater configured to superheat the heated steam mixture discharged from the steam recuperator.

12. 12. The electrolyzer system of claim 11, wherein the mixer is configured to mix hydrogen with the steam received from the primary steam generator and the auxiliary steam generator at least during a start-up mode.

13. An electrolytic cell system as described in claim 1, wherein the electric air heater further comprises a bottom heating element positioned below the stack.

14. The central heating element is disposed in a first zone, a third zone, and a second zone located between the first zone and the third zone; 2. The electrolyzer system of claim 1, wherein the electric air heater comprises a power supply configured to independently control the central heating element in each of the first zone, the second zone, and the third zone.

15. The peripheral heating elements are arranged in a first zone and a second zone arranged below the first zone; 2. The electrolyzer system of claim 1, wherein the electric air heater includes a power supply configured to independently control the peripheral heating elements in the first zone and the second zone.

16. The method of claim 15, further comprising: a hot box including an inner shell and an outer shell surrounding the inner shell; the hot box houses the central column and the stack; 2. The electrolyzer system of claim 1, wherein the peripheral heating element is disposed between the inner shell and the outer shell.

17. The electrolytic cell system of claim 1, wherein the central column further comprises an air preheater configured to preheat air supplied to the central column by obtaining heat from the hydrogen exhaust.

18. The method of claim 17 further comprising: a heat exchange air recuperator surrounding the stack and configured to heat preheated air received from the air preheater by obtaining heat from the oxygen exhaust; 18. The electrolyzer system of claim 17, wherein the air heater is configured to heat heated air exiting the heat exchange air recuperator.

19. The system further comprises a heat exchange air recuperator disposed within the central column; the heat exchange air recuperator is configured to heat the preheated air received from the air preheater by obtaining heat from the oxygen exhaust; 18. The electrolyzer system of claim 17, wherein the electric air heater is configured to heat heated air exiting the heat exchange air recuperator.

20. An electrolytic cell system as described in claim 1, further comprising a steam heater disposed in the central column and configured to superheat steam supplied to the stack.

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