Steam recycle control

Abstract

To provide a solid oxide electrolyzer cell (SOEC) mechanical system, use of steam, and related safety systems.SOLUTION: An SOEC system includes a stack of electrolyzer cells configured to receive water or steam in combination with hydrogen, and a steam recycle outlet configured to recycle a portion of the water or steam.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate generally to solid oxide electrolysis cell (SOEC) mechanical systems, steam applications, and associated safety systems. [Background technology]

[0002] A solid oxide fuel cell (SOFC) can operate as an electrolyzer to produce hydrogen and oxygen, which is called a solid oxide electrolysis cell (SOEC). In SOFC mode, oxygen ions are transported from the cathode side (air) to the anode side (fuel), driven by a chemical gradient of oxygen partial pressure across the electrolyte. In SOEC mode, oxygen ions are transported from the fuel side to the air side when a positive potential is applied to the air side of the cell. Because the cathode and anode are reversed between SOFCs and SOECs (i.e., the SOFC cathode becomes the SOEC anode and the SOFC anode becomes the SOEC cathode), the SOFC cathode (SOEC anode) can be referred to as the air electrode, and the SOFC anode (SOEC cathode) can 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- ions, forming O 2- After transporting through the solid electrolyte, the ions are oxidized (O 2- The open circuit voltage of an SOFC operating with air and a moist fuel (hydrogen, reformed natural gas) is approximately 0.9V to 1V (depending on the water content), so a positive voltage applied to the air electrode in the SOEC mode raises the cell voltage to a typical operating voltage of 1.1V to 1.3V. Summary of the Invention

[0003] Accordingly, the present invention is directed to various steam recirculation controls that substantially eliminate one or more problems resulting from limitations and disadvantages of the related art.

[0004] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and appended claims when taken in conjunction with the appended drawings.

[0005] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

[0006] The accompanying drawings, which are included to provide a further understanding of the invention, and which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a process flow diagram of an SOEC system according to one exemplary embodiment of the present invention. [Figure 2] FIG. 2 is a simplified process flow diagram of an SOEC system according to another exemplary embodiment of the present invention. [Figure 3] FIG. 3 is a graph showing a linear increase in setpoint for both overall utilization and single pass steam utilization with operating current resulting in non-linear steam and recirculation flow commands to the steam / water flow controller and recirculation blower. [Figure 4] FIG. 4 is a diagram illustrating a user control panel according to an exemplary embodiment of the present invention. [Figure 5A] FIG. 5A is a graph illustrating the reduction in voltage fluctuations according to an exemplary embodiment of the present invention. [Figure 5B] FIG. 5B is a graph illustrating the reduction in voltage fluctuations according to an exemplary embodiment of the present invention. [Figure 6] FIG. 6 illustrates a steam blower controller according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References to specific examples and implementations are made for illustrative purposes and are not intended to limit the scope of the embodiments of the invention or the claims.

[0009] Values ​​and ranges may be expressed herein as "about" one particular value and / or to "about" another particular value. When such ranges are expressed, examples include from one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations, by using the prefix "about" or "substantially," it will be understood that the particular value forms another dimension. In some embodiments, a value "about X" may include a value of + / - 1% X or + / - 5% X. It will be further understood that the endpoints of each range are significant both in relation to the other endpoint and independently of the other endpoint. These values ​​and ranges provide examples, and embodiments of the invention are not limited thereto.

[0010] FIG. 1 is an SOEC system 100 according to one exemplary embodiment of the present invention.

[0011] As shown in FIG. 1 , the SOEC system 100 includes an air conduit 105, an air blower 106, an air inlet 107, a steam conduit 110, a recirculated steam inlet 111, a hot box 150, an optional hydrogen conduit 130, an enriched air outlet 123, an enriched air conduit 125, an enriched air blower 126, a steam and hydrogen product outlet 120, a splitter 160, a venturi flow meter 165, a steam recirculation blower 170, and a heat sensor 175.

[0012] According to one exemplary configuration and operation, steam supplied in steam conduit 110 (e.g., supplying on-site or facility steam at various pressures) can have a temperature of approximately 100°C to 110°C (e.g., 105°C) and a pressure of approximately 1 psig. In various embodiments, steam can be supplied to SOEC system 100 from an external source or can be generated locally. In some embodiments, multiple steam inlets can be configured to receive external and local steam, respectively. Alternatively or additionally, water can be supplied to SOEC system 100 and vaporized.

[0013] The air supply (e.g., ambient air) in air conduit 105 may be at ambient temperature at local atmospheric pressure, which may be approximately −20° C. to +45° C. The air from air conduit 105 is received at air blower 106, and the air discharged by air blower 106 is at a slightly higher temperature than ambient due to the heat of compression. For example, the temperature of the air discharged by air blower 106 may be approximately 30° C. at 1.0 psig, compared to an ambient air temperature of 20° C. The air supply in air conduit 105 is then received at air inlet 107 of hot box 150.

[0014] Hydrogen from optional hydrogen conduit 130 may be needed only for start-up and transients when hydrogen is not otherwise being produced by SOEC system 100. For example, a separate hydrogen feed stream or hydrogen recycle steam may not be needed at steady state. The pressure of this hydrogen stream is a design option determined at the time of on-site construction and may be between about 5 psig and 3000 psig. The temperature may be near ambient, as it may come from a reservoir.

[0015] The air supply in air conduit 105, the steam supply in steam conduit 110, and the optional hydrogen supply in hydrogen conduit 130 are fed to hot box 150. Hot box 150 also outputs steam and hydrogen product H-H0-G at steam and hydrogen product outlet 120 of hot box 150, where G represents gross. Hot box output H-H0-G can have a temperature of about 100°C to 180°C (e.g., 130°C) and a pressure of about 0.1 psig to 0.5 psig.

[0016] Additionally, the hot box effluent H-H0-G is fed to splitter 160 and split into a vapor recycle stream RECH2OLP (where LP stands for low pressure) and a pure product H-H0-N (where N stands for net) (e.g., effluent for commercial use or storage). Here, the pure product H-H0-N can have a temperature of about 100°C to 180°C (e.g., 130°C) and a pressure of about 0.1 psig to 0.5 psig. The vapor recycle stream RECH2OLP can have a temperature of about 100°C to 180°C (e.g., 130°C) and a pressure of about 0.1 psig to 0.5 psig. The hot box 150 may further discharge enriched air at enriched air outlet 123 via enriched air conduit 125, which may have a temperature of approximately 120°C to 300°C at essentially local atmospheric pressure (e.g., less than 0.5 psig or less than 0.05 psig).

[0017] The steam recycle stream RECH2OLP is supplied to steam recycle blower 170. The resulting recycle steam REC-STM can have a temperature of about 100°C to 180°C (e.g., 140°C, 154°C) and a pressure of about 0.5 psig to 1.5 psig (e.g., about 1 psig) and is supplied to hot box 150 at recycle steam inlet 111. In some embodiments, a recycle hydrogen feed may not be included with the recycle steam.

[0018] As can be seen from FIG. 1 , the inlet steam temperature (e.g., 105° C.) in steam conduit 110 is low compared to SOEC configurations with internal steam generation. In various configurations, multiple recirculation loops can be configured for SOEC systems using both internal and external steam generation. As shown, recirculation steam inlet 111 is configured to receive steam from steam conduit 110. Here, embodiments optionally direct the steam supplied to the facility from steam conduit 110, which is typically saturated and at a temperature of about 105° C., through internal steam generation coils, one or more vaporizers, and / or other heating elements, and use the air exhaust heat (e.g., about 280° C.) to further heat (i.e., superheat) the steam supply before the heat is released in enriched air conduit 125 through optional fan or enriched air blower 126.

[0019] 2 is a simplified process flow diagram of an SOEC system 200 according to another exemplary embodiment of the present invention. The components of SOEC system 200 are similar to the components of SOEC system 100 described in connection with FIG. 1, and the following describes differences and / or additional features between systems 200 and 100.

[0020] In operation, a mixture of hot (e.g., superheated or ultraheated) steam (e.g., above 110°C) and hydrogen flows across the fuel electrode and an electric current / voltage is applied, resulting in an electrochemical reaction in the solid oxide electrolyzer stack in the hot box 150. In some instances, a low percentage of hydrogen (e.g., from the hydrogen product outlet 120 or hydrogen conduit 130) at the fuel electrode inlet is required to prevent oxidation of the fuel electrode (e.g., nickel oxidation).

[0021] In some operating conditions, when no hydrogen is produced by the electrochemical reaction, the hydrogen required for the fuel electrode is provided by one or more external sources (e.g., from hydrogen conduit 130). However, when the system is in a hydrogen production state, the hydrogen required for the fuel electrode can be provided by recycling a portion of the fuel electrode outlet stream with hydrogen generated by the electrochemical reaction (e.g., hydrogen product outlet 120 and recycled steam inlet 111). Recycling can also increase the overall steam utilization rate by recycling a portion of the unused steam. The overall utilization rate is the ratio of the required steam to the supplied steam (e.g., steam conduit 110). By recycling a portion of the unused steam, the single-pass steam utilization rate is lower than the overall steam utilization rate. The single-pass steam utilization rate is the ratio of the required steam to the sum of the supplied steam (e.g., steam conduit 110) and recycled steam (e.g., steam from hydrogen product outlet 120), as shown in FIG. 2.

[0022] One or more control signals are provided to each of the steam / water flow controllers (not shown) and the recirculation blower (e.g., steam recirculation blower 170) to allow smoothing of the electrochemical voltage while ramping hydrogen production (e.g., from zero to maximum hydrogen production and vice versa). Ramping of hydrogen production occurs during start-up and shutdown, as well as when an alarm occurs that interrupts hydrogen production status, and when hydrogen production status is restored after the alarm is cleared.

[0023] The reduced voltage fluctuations will prevent localized depletion and the appearance of localized hot and cold spots along the electrolysis cells, thereby increasing the lifespan of the stack. Renewable green hydrogen production requires that the hydrogen production rate be ramped up and down to suit the available renewable electricity.

[0024] The amount of steam flow required for the electrochemical reaction to produce hydrogen is proportional to the required hydrogen production rate and inversely proportional to the overall utilization set point, which is directly proportional to the operating current.

[0025] The steam flow set point is calculated as follows:

[0026]

number

[0027] Additionally, the amount of recirculation flow required in the system is calculated as follows:

[0028]

number

[0029] In various embodiments, the calculated (i.e., dynamic) overall utilization and calculated (i.e., dynamic) single-pass utilization set points are used to generate control signals for a steam / water flow controller (not shown) and a recirculation blower (e.g., steam recirculation blower) that reduce voltage fluctuations during ramping.

[0030] FIG. 3 graphically illustrates the linear increase in setpoints for both overall utilization and single-pass steam utilization with operating current, which results in nonlinear steam and recirculation flow commands to the steam / water flow controller and recirculation blower.

[0031] Furthermore, because the steam flow rate set point is directly proportional to the operating current and inversely proportional to the overall utilization rate set point, the dynamically increasing overall utilization rate set point spans a range of currents over which the steam flow rate increases, as shown in Figure 3. This allows for stable operation of the vaporizer (in the internally generated steam unit) for steam generation at the desired temperature. As a result, faster ramping between zero and maximum hydrogen production can be achieved.

[0032] 4 illustrates a user control panel 400 according to an exemplary embodiment of the present invention. In various embodiments, the set points for the overall utilization and single pass utilization can each be ramped to a user-defined final current (e.g., a maximum current or a value less than the maximum current) based on a user-input initial current (e.g., 0 amps or a value greater than 0 amps), as shown in FIG.

[0033] By using calculated overall utilization and calculated single-pass utilization set points, significant reduction in voltage fluctuations during ramp-up and ramp-down (e.g., ramping from zero to maximum hydrogen production and back) is achieved. Figures 5A and 5B graphically illustrate voltage fluctuation reduction according to an exemplary embodiment of the present invention. Figure 5A illustrates a calculated utilization approach, in which segment voltage fluctuations are reduced (i.e., smoothed) throughout ramp-up. In contrast, Figure 5B illustrates a constant utilization approach, in which segment voltage fluctuations increase during ramp-up.

[0034] A calculated total and single-pass steam utilization approach that dictates dynamic nonlinear flow rates of both steam and recirculation during ramping results in lower voltage fluctuations compared to constant utilization, constant flow, or partial constant utilization and partial constant flow approaches.

[0035] Thus, various embodiments provide control of steam flow rate and recirculation flow rate that significantly reduces voltage fluctuations during ramping. Embodiments provide dynamic overall and single-pass utilization setpoints during ramp-up and ramp-down that establish dynamic steam flow rate and recirculation flow rate setpoints. The use of dynamic setpoints reduces voltage fluctuations while enabling faster ramping from zero to maximum hydrogen production. Furthermore, embodiments protect the stack (i.e., extend its life) during operation for a longer period by reducing fluctuations. Localized depletion and localized hot and cold spots along the stack are prevented. Embodiments further provide faster ramping when the internally generated steam of a solid oxide electrolyzer system is integrated with renewable resources that are intermittent in nature (e.g., solar, wind, hydropower, etc.).

[0036] As described herein, embodiments vary the recirculation flow rate based on the use of calculated set points. One or more controllers (e.g., embedded controllers) may be used. Embodiments improve recirculation performance and maintain a steam recirculation blower (e.g., steam recirculation blower 170) within its optimal temperature and pressure operating range. In various embodiments, the recirculation hardware speed is controlled during the electrolysis process.

[0037] FIG. 6 illustrates a steam blower controller 690 according to an exemplary embodiment of the present invention.

[0038] During operation, information exchange 600 occurs between the controller 690 and a steam recirculation blower (e.g., steam recirculation blower 170). The controller 690 (e.g., an embedded controller in a system enclosure adjacent to the hot box 150) directs the steam recirculation blower to recover unused steam from the electrolysis reaction and return it to a steam inlet (e.g., recirculation steam inlet 111) to maximize overall process efficiency. For example, the controller 690 establishes a flow rate setpoint based on efficiency and performance calculations to meet overall system demand. In some examples, the steam blower controller 690 receives flow rate setpoints from other segments of the embedded controller. Additionally, pressure and temperature sensors are used to calculate a readback (i.e., feedback) flow rate using a venturi flow meter 665 (e.g., venturi flow meter 165). The readback flow rate signal is filtered by a low-pass filter 675 and provided to the steam blower controller 690, which can calculate the appropriate blower speed hardware command.

[0039] In some embodiments, the maximum and minimum allowable blower commands are determined by one or more of a safe temperature upstream of the steam recirculation blower, a minimum speed to avoid steam backflow through the recirculation line, and a maximum speed to avoid an overpressure event.

[0040] During operation, steam blower controller 690 is configured to monitor and control the steam recirculation blower (e.g., steam recirculation blower 170). For example, steam blower controller 690 uses one or more sensors (e.g., pressure sensor on the recirculation line, thermal sensor 175) to identify possible thermal or backflow events and blower readback deviations. If any event or safety event is detected, steam blower controller 690 sends one or more commands to place the system in a safe state to protect the hardware. Thus, efficient and safe control of the SOEC steam recirculation loop is achieved through a combination of flow calculation, speed and flow control, temperature management, and pressure event control.

[0041] Additionally, embodiments provide a control technique that allows active control of the operating temperature upstream of the vapor recirculation blower of a solid oxide electrolysis cell (SOEC). In some embodiments, two temperature limiters, such as a maximum temperature limiter 681 and a minimum temperature limiter 682, are configured to control the temperature range of the recirculation blower controller. These temperature limiters 681, 682 set the maximum and minimum allowable speeds of the recirculation blower and govern its hardware speed. The temperature limiters 681, 682 utilize one or more thermal sensors on the recirculation line. The temperature readback is compared to the operating limits of the blower hardware, and then the maximum and minimum allowable blower commands are set as upper and lower CV (control variable) limits in the vapor blower controller block.

[0042] Here, the controller 690 includes a range of commands from the maximum allowable blower speed and the minimum allowable blower speed. The maximum temperature limit ensures that the blower does not operate in a temperature range that may impair its durability and performance. The minimum temperature limit ensures that the steam blower runs fast enough to avoid condensation of liquid water in the steam recirculation line and to avoid possible damage to the system.

[0043] Using various embodiments reduces or avoids condensation of water downstream of the recirculation blower, prevents condensation from being returned to the hot box (e.g., hot box 150), provides at least a minimum flow rate to the steam recirculation line, and the system shuts down if it cannot guarantee a temperature range (e.g., at thermal sensor 175 downstream of steam recirculation blower 170). Increasing the blower speed circulates more flow, raising the upstream temperature. Similarly, reducing the blower speed, commanding less flow, reduces the temperature in the steam recirculation loop.

[0044] The minimum temperature control action increases the recirculation blower speed to avoid liquid water in the steam recirculation line, while the maximum temperature control action decreases the blower speed to avoid temperature regions that could damage the blower.

[0045] In each of the various embodiments described herein, one or more sensors or detectors can be used to detect safety events. For example, one or more pressure detectors and one or more heat detectors can be used. One or more pressure detectors can be placed along the supply hydrogen conduit to detect underpressure (e.g., less than 5 PSI) and overpressure. If a pressure detector trips, the system (i.e., hot box 150) shuts down. Additionally, one or more heat detectors can be placed within the hot box cabinet to detect excessive heat (e.g., greater than 230°C). Cabinet ventilation is provided and maintained, for example, by enriched air blower 126. If a heat detector trips, the system (i.e., hot box 150) shuts down.

[0046] The SOEC system (e.g., 100) stops receiving hydrogen when the SOEC system is operating at steady state or upon detection of a safety event. Additionally, the stack of electrolysis cells in the hot box 150 can be configured to receive hydrogen during startup, shutdown, or when the SOEC system is not producing hydrogen or is not producing enough hydrogen.

[0047] Thus, various embodiments provide an SOEC mechanical system and associated safety systems. To operate an SOEC, mechanical systems and components are required to provide water, air, and starting fuel. Safety systems also protect the system from fire and other damage to the environment and nearby personnel. Operating an SOEC with the necessary safety systems prevents harm and danger resulting from hydrogen leaks and / or other failures. Other SOEC systems may include hazardous location equipment or dual containment of fuel components.

[0048] It will be apparent to those skilled in the art that various modifications and variations can be made in the steam recirculation control of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1. a stack of electrolysis cells configured to receive the steam in combination with hydrogen; a hot box having a stack of electrolysis cells disposed therein; a steam recycle outlet configured to recycle a portion of the steam; a hydrogen conduit located outside the hot box and fluidly connected to the stack of electrolysis cells; Controller and 1. A SOEC system comprising: the hydrogen conduit is configured to supply external hydrogen to the stack of electrolytic cells upon start-up of the SOEC system, and the controller is configured to send a command to the SOEC system to stop supplying the external hydrogen to the stack of electrolytic cells when the SOEC system is operating in a steady state or when the SOEC system detects a safety event. SOEC system.

2. 10. The SOEC system of claim 1, wherein a flow of hydrogen and steam exhaust is recycled back to the stack.

3. 3. The SOEC system of claim 2, further comprising a splitter that supplies a portion of the hydrogen and steam exhaust to a steam recycle blower.

4. The SOEC system of claim 3 , wherein the vapor recirculation blower is controlled by the controller.

5. 4. The SOEC system of claim 3, wherein the steam recirculation blower is controlled by the controller, the controller being integrated into the hot box.

6. The SOEC system of claim 4 , wherein commands to the steam recirculation blower are established according to one or more set points.

7. The SOEC system of claim 4 , wherein commands to the steam recirculation blower are determined according to one or more pressure sensors.

8. The SOEC system of claim 1, wherein the controller is further configured to send a command to the SOEC system so that the stack of electrolytic cells receives the external hydrogen when the SOEC system is shut down or when the SOEC system is not producing hydrogen.

9. The SOEC system of claim 1, wherein the controller is further configured to send a command to the SOEC system so that the stack of electrolytic cells receives hydrogen when the SOEC system is using a renewable energy source.

10. The SOEC system of claim 1 , wherein the safety event is detected by a pressure detector or a thermal detector.

11. 10. The SOEC system of claim 1, wherein the steam discharged by the steam recycle outlet is mixed with hydrogen and the combination of steam and hydrogen is provided to the recycle steam inlet.

12. A method of operating an SOEC system, comprising: receiving steam in combination with hydrogen in a stack of electrolysis cells disposed within the hot box; recirculating a portion of the steam at a steam recycle outlet; supplying external hydrogen to the stack of electrolysis cells from outside the hot box during start-up of the SOEC system; During steady-state operation of the SOEC system, stopping the supply of external hydrogen to the stack of electrolysis cells; when the SOEC system detects a safety event, stopping the supply of hydrogen to the stack of electrolysis cells; A method of operating an SOEC system, comprising:

13. The SOEC system of claim 1, wherein the hydrogen and steam exhaust streams recycled back to the stack are maintained at a temperature of 100°C or greater.

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