How to control an electrolyzer cell stack

Abstract

The present invention provides a method for controlling an electrolyzer cell stack in a system having a fluid temperature control system, a current control system, a voltage monitoring system, and a fluid inlet and outlet temperature monitoring / control system, by controlling the current to a fixed value, calculating the temperature delta between the fluid inlet and the fluid outlet, and adjusting the fluid input temperature if the delta is greater than a threshold. The present invention also provides a method for determining the operating conditions of the stack when the temperature delta measured as described above is lower than a threshold. The present invention also provides a control device and a computer program capable of performing the method outlined above.

Description

[Technical Field]

[0001] The present invention relates to a method for controlling an electrolyzer cell stack, and more particularly to a method for controlling the operating state of an electrolyzer cell stack in an electrolyzer in order to extend the life of the stack and to detect thermal runaway or failure within the stack. [Background technology]

[0002] An electrolyzer may consist of one or more stacks of electrolyzer cells, commonly known as electrolyzer cells or regenerative fuel cells. An electrolyzer is used to separate a source fluid into its constituent components and therefore requires a power source to supply current and voltage across / through at least one stack of electrolyzer cells. For example, electrolyzers may be used to produce hydrogen and oxygen from water, or carbon monoxide and oxygen from carbon dioxide, respectively, through electrolysis.

[0003] The collection and use of the generated oxygen is important because it can be used for industrial and medical applications, among many other uses. Carbon monoxide is also useful in many chemical processes. The collection and subsequent storage and / or distribution of the generated hydrogen is also important because it is a fuel that can help in the race to achieve decarbonization and net-zero targets. The generated hydrogen can be used as a fuel for combustion or as a fuel for fuel cell systems to recombine hydrogen with oxygen through electrolysis to produce electrical and thermal output. Hydrogen has many other uses as well.

[0004] Combining electrolysis with green energy sources could significantly contribute to the green certification of electrolysis, particularly hydrogen uptake, and is therefore important as it can accelerate the achievement of net-zero and decarbonization targets.

[0005] Given the importance of electrolyzers in achieving net-zero and decarbonization targets, and in industry as a whole, any improvement in the efficiency or lifespan of electrolyzers is considered important and valuable.

[0006] One region where electrolyzer efficiency is known to decrease is as the electrolyzer cell stack approaches the end of its usable life. As the stack begins to fail or degrade, the electrolyzer's operating efficiency decreases. For example, as the electrical resistance of the stack increases, a higher voltage is required to carry the same current. However, degradation itself is not a problem that can be easily avoided, but rather is recognized as inevitable. Therefore, compensating for degradation is an important operational consideration when maintaining useful operating capability from the electrolyzer. However, it is also important to manage the operating condition of the electrolyzer in order to minimize degradation and, consequently, reduce the maintenance or downtime costs of the electrolyzer.

[0007] One known method for managing the operating state of an electrolyzer is to operate it at a fixed voltage. There may be advantages to doing so, as some degradation and failure modes are related to or caused by overpotentialing. Therefore, allowing voltage increases may increase the risk of new failure modes occurring in the short term or early in the electrolyzer's lifespan. However, a drawback of this strategy is that as the stack degrades, the current gradually decreases over time, leading to a decline in the system's hydrogen production rate. As a result, it becomes necessary to compensate for the production capacity lost over time by introducing additional electrolyzer cell modules or stacks or by replacing stacks and incurring downtime, all of which increase costs and interruptions, some of which require changes to infrastructure or more space.

[0008] Other prior art teachings, such as JP2020128576 and W02020201485, consider the relationship between temperature control and voltage control in electrolyzer cells to increase the service life of the electrolyzer cells. WO2018033948 further considers current control, employing either a constant current or a constant voltage, in addition to temperature control. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] This invention aims to further advance these concepts. Therefore, it seeks to improve the stack or extend its service life, thereby maintaining the operational reliability of the electrolyzer over a longer period. The invention also seeks to identify when stack failures occur near the end of their service life. [Means for solving the problem]

[0010] According to the present invention, a method for controlling the electrolyzer cell stack of an electrolyzer in an electrolyzer system, The electrolyzer cell stack comprises a fluid inlet and one or more fluid outlets. The electrolyzer system is A fluid temperature control system for controlling the temperature of the fluid entering the electrolyzer cell stack at the fluid inlet, A current control system for controlling the current supply to the electrolyzer cell stack, A voltage monitoring system for determining the stack operating voltage across an electrolyzer cell stack, An inlet temperature monitoring and / or control system for determining the inlet temperature at the fluid inlet, An outlet temperature monitoring and / or control system for determining the outlet temperature at at least one of one or more fluid outlets, Includes, Controlling the current supply to the electrolyzer cell stack to a fixed input current, Calculating a temperature delta by subtracting the determined inlet temperature from the determined outlet temperature, including, i) If the absolute value of the temperature delta is greater than a threshold value, the following equation: T new = T old + (dT × TΔ) where, T new is the adjusted target input temperature, T old is the current (target) input temperature, dT is an adjustment coefficient less than 1 and greater than 0, TΔ is the calculated temperature delta, A method is provided that includes adjusting the inlet temperature using.

[0011] In some embodiments, the method also ii) If the absolute value of the temperature delta is lower than the threshold value, Determining the operating voltage across the electro-lyzer cell stack, Determining the operating state of the stack depending on whether the determined operating voltage is below a voltage threshold, including further steps.

[0012] In some embodiments, the electro-lyzer cell stack comprises at least one fluid inlet for fuel and at least one fluid inlet for sweep gas.

[0013] In some embodiments, the electro-lyzer cell stack comprises at least one cathode-side fluid outlet and at least one anode-side fluid outlet.

[0014] In some embodiments, the electro-lyzer system includes a fluid entering the electro-lyzer cell stack at a fluid inlet and a fluid temperature control system for controlling the temperature of the fluid entering the electro-lyzer cell stack.

[0015] In some embodiments, the current control system provides or controls the input current that powers the electrolyzer cell stack.

[0016] In some embodiments, the voltage monitoring system includes a voltage sensor for detecting the stack operating voltage across the electrolyzer cell stack.

[0017] In some embodiments, the outlet temperature monitoring and / or control system includes a temperature sensor for detecting the output temperature at at least one of the fluid outlets.

[0018] In some embodiments, this method is Set a target input temperature at at least one fluid inlet, Controlling the fluid temperature of the fluid entering the electrolyzer cell stack at at least one fluid inlet to a target value which is the target input temperature, In order to operate the electrolyzer cell stack with a constant current, a constant input current is supplied to the electrolyzer cell stack, The voltage monitoring system detects or determines the operating voltage across the electrolyzer cell stack, Includes.

[0019] In other embodiments, the temperature may vary from a target value, or the target value may be a temperature range, or the temperature is set by the supply temperature and heating thereof, and this method maintains a fixed current, a fixed voltage, and a fixed temperature delta, and attempts to adjust the inlet temperature, target value, or temperature range as needed according to the method of the present invention.

[0020] In some embodiments, the outlet temperature monitoring and / or control system detects the output temperature at each fluid outlet.

[0021] In some embodiments, the inlet temperature monitoring and / or control system detects the input temperature at the fluid inlet or at each fluid inlet.

[0022] In some embodiments, various temperature delta thresholds can be set. For example, if the electrolyzer has multiple stacks, each may have a different temperature delta threshold.

[0023] In some embodiments, this method includes setting maximum and minimum stack voltage thresholds for the stack or each stack.

[0024] In some embodiments, different dTs are applied to each stack of the electrolyzer or electrolyzer system. This may be advantageous in ensuring that not only each stack but the system as a whole becomes thermoneutral. Similarly, dTs may be set to provide a “bias” toward the exothermic operation of each (or some) of the stacks. This may be to generate excess heat to compensate for heat losses in the system’s heat exchangers or other inefficiencies in the system.

[0025] In some embodiments, if the absolute value (i.e., coefficient) of the temperature delta is less than the temperature delta threshold, the method includes checking the detected operating voltage against the voltage thresholds of the maximum and / or minimum stacks, and if it exceeds the voltage threshold of either stack, the method includes issuing a warning or alarm, or shutting down the stack by reducing or turning off the input current.

[0026] According to the present invention, in some embodiments, if the determined operating state of the stack is a potential runaway, the method includes either issuing a warning or shutting down the stack, or both.

[0027] In some embodiments, the voltage threshold is related to the optimal voltage for achieving a thermoneutral condition at a given temperature.

[0028] In some embodiments, the voltage threshold is the optimal voltage minus a predefined delta.

[0029] In some embodiments, if either or both of the stack's voltage thresholds are exceeded, this method includes attempting to operate the stack at a constant potential at the thresholds.

[0030] In some embodiments, this method includes setting a maximum inlet temperature threshold and switching the operating mode from constant current to constant potential when the inlet temperature reaches the maximum inlet temperature threshold.

[0031] In some embodiments, the electrolyzer cell stack is a solid oxide type electrolyzer cell stack.

[0032] In some embodiments, the electrolyzer comprises more than one stack. The stacks may be electrically connected in parallel or in series.

[0033] In some embodiments, this method is applied individually to each stack. Alternatively, this method is applied to the entire stack, where the output temperature is the temperature at the fluid outlet of the entire stack, and the input temperature is either the target input temperature of the entire stack or the measured temperature of the entire stack.

[0034] In some embodiments, this method aims to operate the stack in a thermoneutral state such that the temperature within the stack remains substantially constant.

[0035] According to the present invention, when the absolute value of the temperature delta (i.e., the coefficient) is greater than the temperature delta threshold, the adjustment of the target input temperature is applied such that if the temperature delta is positive, the adjustment of the target input temperature is also positive, and if the temperature delta is negative, the adjustment of the target input temperature is also negative. This is counterintuitive, as in the prior art, it is usually desirable for heating stacks to be cooled, while for cooling stacks to be heated. However, the present invention relies on the resistance response to the stack temperature and the interaction between this resistance and the voltage across the stack under constant current conditions. When the input temperature is increased, the stack warms up. This reduces the electrical resistance of the stack and also reduces the voltage across the stack. This decrease in voltage under constant current conditions (i.e., constant current) reduces the power consumption of the stack, and therefore, if it falls below the thermoneutral voltage, the endothermic nature of electrolysis may actually cause the stack to avoid heating by the amount of the increase in input temperature, and may even be cooled. Conversely, when the input temperature is decreased, the stack cools down. This increases the electrical resistance of the stack and also increases the voltage across the stack. An increase in voltage under these constant current conditions (i.e., constant current) increases the power consumption of the stack, and therefore, when it exceeds the thermoneutral voltage, the heat generated by the configuration (due to the increased power input from the constant current source) can actually cause the stack to be heated, thus avoiding cooling by the amount of the input temperature drop.

[0036] Accordingly, the present invention provides tuned internal temperature control of a stack using external fluid temperature control, constant current conditions across the stack, and power consumption characteristics of the stack resulting from voltage fluctuations on either side of the stack's thermoneutral voltage.

[0037] Furthermore, the present invention makes it possible to compensate for the inevitable degradation of the electrolyzer cell. As the cell degrades, its resistance increases, and therefore, power consumption increases (to maintain a constant current). The present invention makes it possible to compensate for the increased power consumption, and ultimately the increase in the operating temperature of the stack, by increasing the input temperature. Thus, the stack can be controlled to maintain a constant current (constant current) condition along with a thermoneutral voltage condition, even if the stack degrades (at least up to the maximum temperature at which constant potential operation is preferable).

[0038] Certain embodiments of the present invention also provide “runaway” protection in the case of vapor electrolysis when a leak begins to occur that could cause hydrogen to mix with oxygen. Even if initially small, such a leak, for example on the output side of the stack, can lead to the combustion of hydrogen and oxygen in hot air or an oxygen-rich sweep flow. This combustion can eventually cause alternative heating of the stack, but initially it causes a short circuit across the stack or faster degradation of the electrolyte or anode or cathode. In other words, a leak that causes internal combustion can result in a balanced temperature change (the temperature drops due to the leak, but rises due to the subsequent combustion), making it difficult to detect such a leak.

[0039] Leaks provide an additional heat source, as the generated hydrogen fuel reacts with oxygen to produce steam, releasing heat in the process. It is desirable to monitor the magnitude of internal leaks within the stack so that a preventative shutdown can be initiated if this increases beyond a certain maximum value. This prevents thermal runaway and allows for the recovery and repair of the stack.

[0040] Because the control system works to maintain thermoneutrality, the effective stack voltage drops when leakage occurs. This means that the stack voltage can be used as an approximate gauge of the amount of leakage inside the stack. Since no additional measurement system is required and the stack voltage is already being monitored, this could be very practical as a further monitoring mechanism.

[0041] Small leaks or cell failures may not produce a significant temperature delta. In fact, initially, the failure may only be identified by a voltage change across the stack. If this change becomes large, it can trigger a warning or alarm, or even a shutdown of the electrolyzer system.

[0042] Therefore, certain embodiments of the present invention make it possible to avoid missed leak detections that do not exhibit changes in the system's output temperature. The present invention also compensates for such degradation by operating the electrolyzer system at a modified input temperature and a corresponding output temperature, ensuring that both constant current and thermoneutral conditions continue to be observed, thus extending the lifespan of the electrolyzer cell stack and, similarly, maximizing the performance and efficiency of the stack near the end of its lifespan. Furthermore, since constant current and thermoneutral conditions are considered optimal operating conditions for the efficient electrolysis of water (or carbon dioxide), it is possible to use the electrolyzer in a manner that maximizes the amount of hydrogen produced for a given electrical input over a longer period of time.

[0043] Since the method of the present invention is typically performed at set time intervals, the temperature delta over this given period is taken into account, thereby avoiding false detections from instantaneous or periodic spikes. Accordingly, in some embodiments, detecting or determining the operating voltage across the electrolyzer cell stack and / or detecting or determining the output temperature at the fluid outlet with a voltage sensor is performed periodically at predetermined time intervals. For example, time intervals of 10 minutes, 30 minutes, 1 hour, or shorter or longer time intervals. In particular, if a number of persistent problems are detected, i.e., if some data points or readings show a change, the present invention can be triggered to respond by issuing a warning or initiating a shutdown. Thus, a moving average of a series of samples acquired over a specified period can be used to determine temperature measurements while avoiding the influence of out-of-range or erroneous data points. The same or similar process can be applied to voltage measurements.

[0044] Stack voltage can be measured directly or estimated from voltage measurements across a single cell or a sample of cells. Similarly, inlet / outlet temperatures can be measured directly or estimated from sensor measurements upstream / downstream of the inlet / outlet.

[0045] Typically, temperature changes are small, so the threshold temperature delta can be as small as 1, 2, or 5°C. Therefore, in some embodiments, the temperature delta threshold is set to a value within the range of 1 to 5°C.

[0046] In some embodiments, the temperature delta may include an offset (e.g., 1, 5, or 10°C) to allow the stack to generate some excess heat. This makes it possible to eliminate or reduce the use of electric heaters in the system.

[0047] In some embodiments, this method also monitors the output fluid to check, for example, the output volume of hydrogen or oxygen from the stack. Therefore, this method can monitor the output fluid to check the target gas output volume or percentage from the stack. If there is a leak and combustion occurs, the volumes of hydrogen and oxygen will decrease. The water content of the oxygen output may also increase. These can also provide quantitative indicators of failure.

[0048] This method can be configured to trigger an alarm, warning, or shutdown procedure when hydrogen leaks into oxygen, resulting in a failure equivalent to 5 to 10%, by adjusting the voltage delta from a known ideal thermoneutral voltage at a given temperature. The cost of repairing or replacing the cell, as well as the risk of catastrophic failure that may occur if larger leaks are not repaired, can be calculated. This can be done to determine at what point it is best to replace or repair the stack compared to continuing to operate the electrolyzer stack in a state of reduced efficiency. Ultimately, the goal is to maximize the amount of hydrogen produced by the stack relative to its maintenance and operating costs (referred to as the hydrogen "equalization" cost).

[0049] The present invention is particularly applicable to electrolyzers in the fields of medium-temperature and high-temperature electrolyzer cells, and also to electrolyzer cell temperatures at lower temperatures, although still above 100°C, and therefore operating with steam rather than water. However, water-based electrolyzers (operating at temperatures below 100°C) may also benefit from the present invention.

[0050] In some embodiments, at least one electrolyzer cell is a solid oxide type electrolyzer cell, i.e., the electrochemically active region is a solid oxide. Solid oxide type electrolyzer cells (SOECs) typically operate in the temperature range of 400–900°C, and for some chemicals, in the temperature range of 400–700°C, or more specifically, 450–650°C. Such electrolyzer cells may be called medium-temperature solid oxide type electrolyzer cells, or IT-SOECs.

[0051] The advantage of steam-based electrolyzers is that, in steam electrolysis, particularly in medium and high-temperature steam electrolysis above 400°C, the high-temperature environment allows for reduced power requirements compared to the electrolysis of liquid water, thus enabling efficient hydrogen production. Furthermore, the higher the temperature, the relatively higher the reactivity with the electrolyzer compared to liquid water. Therefore, the present invention is very suitable for use in solid oxide type electrolyzer cells (or SOECs) operating at temperatures above 400°C (commonly known as medium-temperature SOECs, or high-temperature SOECs above 750°C).

[0052] Many possible forms of SOEC exist, using various electrochemically active electrolyte chemicals. For example, three well-known electrolyte materials are yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), and gadolinium-doped ceria (GDC or CGO).

[0053] Due to the SOEC temperature (usually exceeding 400°C), the water passing through the electrolyzer cell evaporates and becomes high-temperature steam.

[0054] Alternatively, in some embodiments, the electrolyzer cell system comprises high-temperature electrolyzer cells with a stack operating temperature of 750°C to 1100°C.

[0055] In summary, the present invention enables the gradual increase in the stack temperature to control the stack's performance (i.e., current density) while maintaining constant current and thermoneutral conditions throughout the stack's lifespan, which is achieved by controlling the input fluid temperature when necessary.

[0056] The present invention also relates to a control device for controlling the electrolyzer cell stack of an electrolyzer in an electrolyzer system, A fluid temperature control system for controlling the temperature of the fluid entering the electrolyzer cell stack at the fluid inlet of the electrolyzer cell stack, A current control system for controlling the current supply to the electrolyzer cell stack, A voltage monitoring system for determining the stack operating voltage across an electrolyzer cell stack, An inlet temperature monitoring and / or control system for determining the inlet temperature at the fluid inlet, An outlet temperature monitoring and / or control system for determining the outlet temperature at at least one fluid outlet of an electrolyzer cell stack, Equipped with, The current supply to the electrolyzer cell stack is controlled to a fixed input current. The temperature delta is calculated by subtracting the determined inlet temperature from the determined outlet temperature. Adapted to, i) If the absolute value of the temperature delta is greater than the threshold, then the following formula applies: T new =T old +(dT×TΔ) Here, T new This is the adjusted target input temperature. T old This is the current (target) input temperature. dT is an adjustment factor less than 1 and greater than zero. TΔ is the calculated temperature delta. Provide a control device that is further adapted to adjust the inlet temperature using it.

[0057] In some embodiments, the control device is further adapted to determine the operating voltage across the electro - lyzer cell stack when the absolute value of the temperature delta is lower than a threshold value, and to determine the operating state of the stack according to whether the determined operating voltage is below a voltage threshold.

[0058] According to one aspect of the present invention, there is provided a computer program including instructions that cause a computer to execute the steps of the method according to the above - mentioned aspect when the program is executed by the computer. In particular, this method causes the computer to control the current supply to the electro - lyzer cell stack to a fixed input current when the program is executed by the computer, calculates the temperature delta by subtracting the determined inlet temperature from the determined outlet temperature, and i) when the absolute value of the temperature delta is greater than a threshold value, the following formula: T new =T old +(dT×TΔ) where T new is the adjusted target inlet temperature, T old is the current (target) inlet temperature, dT is an adjustment coefficient less than 1 and greater than 0, TΔ is the calculated temperature delta, and includes adjusting the inlet temperature using it.

[0059] According to one aspect of the present invention, there is provided a non - transitory computer - readable medium storing instructions that execute (or cause a processor to execute) the steps of the method according to the above - mentioned aspect when executed by a processor.

[0060] The control device can further be configured to execute the foregoing method and can be implemented with or within any of the electro - lyzer systems described herein.

[0061] Here, the present invention will be described in more detail, merely as an example, with reference to the attached drawings. [Brief explanation of the drawing]

[0062] [Figure 1] This diagram schematically shows a typical electrolyzer cell that can be stacked in large numbers. [Figure 2] This diagram schematically illustrates an example of an electrolyzer system, which includes an external stream channel on the anode and cathode sides of a stack equipped with a heat exchanger and heater for controlling the input fluid temperature. [Figure 3] This is a flowchart illustrating the general steps of the present invention. [Figure 4] This diagram schematically shows a control device for controlling the electrolyzer cell stack of an electrolyzer in an electrolyzer system. [Modes for carrying out the invention]

[0063] Referring first to Figure 1, the basic structure and operation of a typical electrolyzer cell 11 within the electrolyzer 10 of the electrolyzer system 20 are shown with reference to one fuel / electrolyzer cell 11 in the stack 12. Note that other auxiliary components related to the electrolyzer cell 11 are included in the electrolyzer system 20. These typically include heat exchangers, heaters, valves, and sensors.

[0064] Figure 2 schematically illustrates an example of an electrolyzer system 20 similar to that known from WO2023 / 012456, the entire contents of which are incorporated herein by reference. It shows exemplary auxiliary components such as a heat exchanger, heater, and sensors, which are described in more detail below.

[0065] Figure 2 also shows that the electrolyzer system 20 comprises an electrolysis stack 12 containing a stack of electrolyzer cells 11. As shown in the figure, this example has five such cells, but generally, a stack may have tens or even hundreds of cells in parallel, and multiple stacks 12 may be provided connected electrically in series or parallel.

[0066] Referring back to Figure 1, the electrolyzer cell 11 comprises an anode 33, a cathode 34, and an electrolyte 35. Such a structure of the electrolyzer cell 11 is well known in the art. In this example, the electrolysis of water is described, but other gases can be similarly electrolyzed to decompose them into their constituent components, such as decomposing carbon dioxide into oxygen and carbon monoxide.

[0067] In the electrolyzer system 20, if it is desirable to reduce internal heating of the water, a steam source may be used, in which water in the form of steam 43 from a water supply source is flowed to the cathode 34 via the inlet 41, and hot air 42 is flowed to the anode 33 via the inlet 40. To power the electrolyzer cell, current is applied across the electrolyzer cell 11 via electrical terminals / connections 36, 37 on the anode and cathode sides of the electrolyzer cell 11. These terminals can be arranged adjacent to each other on one side or end of the stack 12 of the cells 11 by stacking the cells in parallel and using busbars to extend one terminal to the other end of the stack 12, for example, as is known in the art.

[0068] As a result of the electric current, an electrolysis reaction occurs across the electrolyte 35, oxygen ions flow from the cathode 34 through the electrolyte 35 to the anode 33, some of the vapor is decomposed into hydrogen on the cathode side of the electrolyzer cell 11, and oxygen is produced on the anode side.

[0069] Oxygen is extracted via an airflow or sweep flow provided by the hot air 42 and is therefore discharged from the off-gas outlet 38 on the anode side of the electrolyzer cell 11. Its output is generally oxygen-rich air (an oxygen-rich hot gas flow). Hydrogen, on the other hand, is extracted on the cathode side of the electrolyzer cell 11 and discharged from another off-gas outlet 39. Since the decomposition of vapor into oxygen and hydrogen usually occurs only with respect to a portion of the supplied vapor, this off-gas typically mixes with the remaining vapor. Thus, the hydrogen is discharged as "wet" hydrogen on the cathode side. Therefore, the vapor exiting the cathode side is hydrogen-rich, and the air exiting the anode side is oxygen-rich.

[0070] These off-gas temperatures are typically similar to the operating temperature of the electrolyzer cell 11. However, the specific delta from the input temperature will depend on the amount of power supplied to the electrolyzer and the internal resistance of the cell.

[0071] Such operational characteristics of electrolyzer cells, including SOECs, are well known in the art.

[0072] The high operating temperature of the electrolyzer cell 11 (i.e., above 100°C for a steam electrolyzer and usually above 400°C for a solid oxide electrolyzer cell (SOEC)) allows the heat of the off-gas from the off-gas outlets 38, 39 to be effectively utilized by the electrolyzer system 20 without being wasted, providing, for example, at least some of the heat for steam generation on the input side of the stack, and similarly for heating the hot air entering the electrolyzer before the inlets 40, 41.

[0073] As shown in Figure 2, this can be achieved via heat exchangers 22, 50, and 62. Heaters 36, 52, and 58 can also be provided where needed to raise the temperature of the fluid through the flow lines 54, 56, 18, 24, and 28 between the components of the system 20 when necessary.

[0074] To control this, sensors 64, 66, 68, 70, 72, 74, and 76 may be provided along the flow lines 54, 56, 18, 24, and 28. These will allow control of the flow rates of the respective fluids through the heat exchangers 22, 50, and 62 or through the heaters 36, 52, and 58, for example, the flow rate of air 42 or water 16, or, in this case, the flow rate of off-gas from the stack outlets 46, and 48 connected to the outlets 38, and 39 of cell 11. Thus, the flow rate and / or temperature of the input fluid at the two stack inlets 14, and 44 connected to the inlets 40, and 41 of cell 11 can be controlled as needed, as described later.

[0075] A flow line or channel represents a flow through one or more pipes or lines from one location to another. Therefore, it defines a fluid connection or communication between points.

[0076] Figure 2 shows a sweep gas supply channel 18. This is a sweep gas supply pipe or line 18 that provides fluid communication from the sweep gas supply section 16 (usually air) to the anode-side stack inlet 14.

[0077] Stack 12 also includes an anode-side stack outlet 46, from which anode-side exhaust products (off-gas, usually oxygen-rich air) are typically discharged outside of system 20 for use in any one or more of the various possible purposes, although the heat generated can be effectively utilized within system 20, as will be described later.

[0078] An external fluid stream 26 also flows into the electrolyzer system 20. The external fluid stream 26 is a stream generated separately from the process of the electrolyzer system 10. The external fluid stream 26 can be a high-temperature flow of fluid or gas, for example, an external heat source.

[0079] The external fluid stream 26 is assumed to be exhaust gas from another process and may have low-grade heat (e.g., around 200°C), but various heat sources can be used to provide higher or lower-grade heat to the external fluid stream 26.

[0080] The external fluid stream 26 forms an external stream channel 28. The external stream channel 28 passes through the first heat exchanger 62. The first heat exchanger 62 is located in the sweep gas supply channel 18 between the sweep gas supply unit 16 and the anode inlet 14. Therefore, both the external stream channel 28 and the sweep gas supply channel 18 pass through the first heat exchanger 62 and exchange heat in the first heat exchanger 62.

[0081] Figure 2 also shows that the anode outlet channel 24 from the anode-side stack outlet 46 exits the first discharge section 88 after passing through the second heat exchanger 22 (for example, to be collected and used elsewhere later). This second heat exchanger 22 is also located in the sweep gas supply channel 18. In this embodiment, the second heat exchanger 22 is located in the sweep gas supply channel 18 between the first heat exchanger 62 and the anode inlet 14. Thus, the anode outlet channel 24 and the sweep gas supply channel 18 exchange heat in the second heat exchanger 32.

[0082] During the operation of system 10, the exhaust gas may contain high-quality heat (for example, approximately 550°C in the case of the SOEC electrolyzer system). Therefore, the heat from the exhaust gas can be used to heat the sweep gas supply channel 18 in the second heat exchanger 32. This is beneficial for supplying high-temperature sweep gas at the anode inlet 14 to increase the efficiency of the electrolysis reaction in stack 12.

[0083] A first heater 36 is provided in the sweep gas supply channel 18. In this embodiment, it is located between the second heat exchanger 32 and the anode inlet 14. The first heater 36 is used to heat the sweep gas supply 16 in the sweep gas supply channel 18 when needed. The first heater 36 can be an electric heater or a combustion heater as needed.

[0084] The first heater 34 is also called a trim heater because it provides a small amount of heat to fine-tune the temperature at the anode inlet 14 to ensure a consistent and efficient electrolyzer reaction in the stack 12.

[0085] It is shown that the bypass channel 30 is connected to the sweep gas supply channel 18. The bypass channel 30 is connected at its first end 78 to a point on the sweep gas supply channel 18 between the sweep gas supply unit 16 and the first heat exchanger 62. Thus, the first end 78 is upstream of the first heat exchanger 62. The bypass channel 30 is connected at its second end 80 to a point between the second heat exchanger 22 and the first heater 62. Thus, the second end is downstream of the second heat exchanger 22.

[0086] The bypass channel 36 bypasses the first heat exchanger 30 and the second heat exchanger 32. This allows the sweep gas supply channel 18 to avoid heat exchange with the heat exchangers. This may be beneficial when the thermal energy in the external stream channel 28 and / or anode outlet channel 24 is at a level that is not required for the sweep gas supply channel 18. Such situations may include startup, when the channels may be cold, or cooling, when heat transfer to the sweep gas supply channel 18 is no longer needed and the sweep gas supply 16 is used to cool the system 10.

[0087] The bypass channel 36 can be operated by a control valve 82 or the like. The control valve may be a mechanical or electric control valve set to specific settings for opening or closing, or it may be operated automatically by a controller which may include a processor and memory that can be programmed to operate the control valve manually or, as needed, in specific situations.

[0088] For example, to control flow rate and temperature, one or more of these flow lines may be equipped with one or more sensors 66, 72, 74, 76, and a controller may be connected to these sensors and potentially to a heater and further flow valves or bypasses.

[0089] While the above is presented as shown in Figure 1, it is emphasized that specific variations can be created. In particular, the presence of the first heat exchanger 62, the second heat exchanger 22, the first heater 36, and the bypass channel 30 can be modified as needed for the function of system 10. For example, in some situations, such as when the external fluid stream 26 is high-grade heat, the second heat exchanger 22 may not be required. Further heaters, such as a third heater 58 on the illustrated anode outlet channel 24, can also be provided and controlled to operate when needed.

[0090] Next, referring to the cathode side of the system, a water supply unit 84 is provided, which is connected to the cathode-side stack inlet 44 of the electrolysis stack 12 via a water or steam supply channel 56. The cathode-side stack inlet 44 is connected to a steam inlet 41 on the cathode side of each electrolyzer cell 11 of the electrolysis stack 12. The water supply channel 56 provides a flow, pipe, or line for water or steam to flow into the electrolyzer 10.

[0091] The electrolysis stack 12 also includes a cathode outlet 48, which is the outlet from the cathode of the electrolysis stack 12, and the cathode outlet 48 is connected to the vapor outlet 39 of each electrolyzer cell 11. The cathode outlet 48 is connected to a second discharge section 86 by a cathode outlet passage 54. Wet hydrogen is the exhaust gas on this side of the electrolyzer 10 and can be collected for downstream treatment and use.

[0092] A third heat exchanger 50 is provided in the water supply channel 56 between the water supply section 42 and the cathode inlet 44. The cathode outlet channel 54 passes through the third heat exchanger 50 located between the cathode outlet 48 and the second discharge section 86 of the cathode outlet channel 54. Therefore, heat is exchanged between the cathode outlet channel 54 and the water supply channel 56.

[0093] Products generated in stack 12 and output at cathode outlet 48, such as wet hydrogen, can have high thermal energy (e.g., approximately 550° in the case of an SOEC system). Therefore, this thermal energy can be used to heat the water supply channel 56. This can be beneficial because steam is preferably supplied for the electrolyzer reaction. Thus, in the third heat exchanger 50, thermal energy from the cathode outlet channel 54 can be transferred to the water supply channel 56. This heat exchanger 50 can be called a recovery heat exchanger.

[0094] The product, for example, wet hydrogen, may also be beneficial in the second discharge section 86, as it preferably has lower thermal energy for transfer to other processes and storage. Therefore, heat transfer from the product is beneficial.

[0095] A second heater 52 is provided in the water supply channel 56 to heat the flow path. The second heater 52 is positioned between the third heat exchanger 50 and the cathode inlet 44. Thus, the second heater 52 is downstream of the water supply section 84. The second heater 52 is similar to the first heater 36 in that it can be an electric heater or a combustion heater as needed. The second heater 52 provides further heating to the water supply channel 56 as needed. For this purpose, sensors 64, 68, 70 and a control system can also be provided.

[0096] When high heat is transferred through the third heat exchanger 50, the amount of thermal energy supplied by the second heater 52 can be reduced. On the other hand, when low heat is transferred through the third heat exchanger 50, for example during startup, the amount of thermal energy supplied by the second heater 52 can be increased. This may be beneficial during startup when the system 10 is not yet warm.

[0097] The second heater 52 is also called a trim heater for the same reasons as the first heater 34, as it provides a small amount of heat to fine-tune the temperature at the cathode inlet 44 to ensure a consistent and efficient electrolyzer reaction in the stack 12, but both can also be used for startup heating.

[0098] Therefore, as described above, it is possible to control the input temperature of the fluid entering the electrolyzer 10, particularly the electrolyzer cell stack 12, and thus the electrolyzer cells 11 within it.

[0099] Here, we will further explain the underlying concepts of the present invention by referring again to Figure 1 and then to Figure 3.

[0100] As mentioned above, the off-gas temperature is usually similar to the operating temperature of the electrolyzer cell 11. However, the specific delta from the input temperature depends on the amount of power supplied to the electrolyzer and the internal resistance of the cell. According to the present invention, the stack is powered with a constant current. Therefore, the stack operates under constant current conditions. The electrical resistance of the stack governs the voltage applied across the stack, and therefore, as the resistance changes, the power consumption of the stack changes.

[0101] By reducing the amount of external heat supplied to the system via a fluid temperature control system, the operating efficiency can be optimally improved. For example, if external heat is provided free of charge as a waste product of another industrial process, that external heat can be effectively utilized without cost, i.e., financial efficiency is provided. However, if there are costs associated with that external heat, it would be better to improve the operating efficiency instead. This invention achieves this by employing a thermoneutral voltage across the stack to avoid heat waste in the stack, using a constant current condition in the stack, i.e., a constant current (constant ampere), and under thermoneutral conditions, the electrolyzer is in an adiabatic state, i.e., energy is balanced, meaning that virtually no heat is consumed or released.

[0102] For example, energy input and output are defined as follows: Energy input at thermoneutrality = P stack =V stack ·I

number

number

[0103] Therefore, the thermoneutral voltage of the stack (V TN ) will be as follows:

number

[0104] This assumes ideal insulation, where there is no heat loss or leakage. In reality, neither of these is true, and the energy balance in the real world is as follows:

number

[0105] The inventors of the present invention, LEAK,TOT and Q heat loss We recognized that it is uncontrolled and difficult to measure. Furthermore, these change over time as the stack degrades, and therefore it is very difficult to predict how much actual thermoneutral voltage will be needed. For these reasons, Q heat release V such that = 0 stack Solving the above equation for this is difficult.

[0106] Furthermore, continuously using both a constant voltage and a constant current is impractical, as this leads to other inefficiencies due to fluctuations in the stack's temperature and changes in the stack's electrical resistance over time due to the stack's degradation.

[0107] In the prior art, it is known that either a constant voltage or a constant current is used in the stack, and then the current or voltage is controlled, respectively, to maintain the stack in a substantially thermoneutral condition. This avoids overcooling or overheating of the stack. When the voltage is low (constant current stack, i.e., constant current), the stack exhibits endothermic characteristics, thus cooling the fluid (and the operating temperature of the stack as well), resulting in a fluid output temperature lower than the fluid input temperature. On the other hand, when the voltage is high (constant current stack, i.e., constant current), the stack exhibits exothermic characteristics, thus heating the fluid (and the operating temperature of the stack as well), resulting in a fluid output temperature higher than the fluid input temperature.

[0108] The present invention still uses a constant current condition for the stack, but varies as needed between thermoneutral, overvoltage, and undervoltage conditions in response to input fluid temperature control aimed at maintaining the fluid input temperature equal to the fluid output temperature. This involves measuring the temperature at the inlet and outlet of the stack, and therefore Q heat loss and I LEAK,TOT This is done because the inventors realized that even if we don't know the actual extent of Q, it is relatively easy to automatically control the thermoneutral voltage to a voltage that satisfies the above equation. Under these conditions, Q heat loss = 0, and the fluid input temperature (TstkIn) = the fluid output temperature (TstkOut).

[0109] In other words, the present invention aims to minimize the temperature delta between the fluid output temperature from the stack and the fluid input temperature of the stack, striving for zero delta. This allows for long-term use of the stack under constant current conditions, along with thermoneutral voltage conditions, even if the stack or one or more of its cells degrade, although it is necessary to recognize that there will come a point when the degradation becomes too great and requires an alarm or shutdown of the stack.

[0110] Referring to Figure 3, the method of the present invention operates by checking the fluid output temperature (TstkOut) from the stack and comparing it to the fluid input temperature. Normally, this is the actual input temperature (TstkIn) obtained from a sensor at the input end of the stack, but it may be the target input temperature (TstkInEst). As shown in Figure 3, in this example, the actual input temperature (TstkIn) will be the same as the target input temperature (TstkInEst), since the fluid temperature control system should be able to match the actual temperature to the target temperature. However, this is not always the case, especially if there are changes in the temperature of the source fuel (usually vapor or carbon dioxide) or even the sweep gas.

[0111] This temperature detection can be performed over / after a set period of time, i.e., periodically, for example, every 10 minutes, every 30 minutes, or every hour, or at longer or shorter intervals (in other words, there is a dwell time). This is to avoid one-off measurement reactions that may occur due to accidental peaks or troughs in the data. In fact, the present invention can be carried out almost continuously, and in practice this may involve generating a moving average over a given time or even over several hours to reduce the effects of mismeasurement.

[0112] Therefore, the temperature delta (TstkOut-TstkIn) is calculated and compared with the temperature delta threshold (TstkDeltaDvt).

[0113] If the absolute value of the temperature delta (i.e., the coefficient) is greater than the temperature delta threshold (i.e., |TstkOut-TstkIn|>TstkDeltaDvt), the present invention adjusts the target input temperature using the following formula to maintain the minimum temperature delta: T new =T old +(dT×TΔ) Here, T new This is the adjusted target input temperature (i.e., this becomes TstkIn), Told is the current, now old, target input temperature, dT is an adjustment coefficient less than 1 and greater than zero, TΔ is the calculated temperature delta (TstkOut - TstkIn).

[0114] The method then returns to the next detection cycle (and dwell time).

[0115] Instead, if the absolute value of the temperature delta (i.e., the coefficient) is less than the temperature delta threshold (i.e., |TstkOut - TstkIn| < TstkDeltaDvt), instead, the present invention checks the detected operating voltage against the voltage threshold of the minimum stack. This is set as a given delta from the optimal voltage determined beforehand to achieve thermoneutral conditions at a given temperature, or more generally, at a selected temperature. Depending on whether the stack is operating below or within this voltage range, the operating state of the stack can be diagnosed.

[0116] This is shown in FIG. 3 as VPwRDcStkTN - VPwRDcStkDvt < VPwRDcStkAct. VPwRDcStkTN is the thermoneutral voltage under adiabatic conditions (meaning "Voltage - PoweR" "Direct - current" "Stack" "Thermal Neutral"), and in the case of water to hydrogen, it is typically approximately 1.28 V per cell. VPwRDcStkDvt is the maximum allowable deviation from VPwRDcStkTN (meaning "Voltage - PoweR" "Direct - current" "Stack" "Deviation"). This can be different for voltage increases and voltage decreases (+ and -). VPwRDcStkAct is the actually measured voltage (meaning "Voltage - PoweR" "Direct - current" "Stack" "Actual"). In other words, the actual voltage (VPwRDcStkAct) needs to exceed the ideal value (VPwRDcStkTN), but a certain deviation (VPwRDcStkDvt) is allowed. In one example, the allowable deviation is up to 30 mV.

[0117] This threshold acts as protection against runaway events (e.g., the occurrence of progressive leaks) and other problems (e.g., signal or cell failures, or fluid flow path failures).

[0118] If the determined stack voltage threshold falls below the minimum threshold (as shown in Figure 3, "No"), this indicates a potential runaway leak, and the system may be prompted to issue a warning or alarm, or it may be possible to initiate a shutdown of the stack, for example, by reducing or turning off the input current. Otherwise, the loop returns to the next read.

[0119] Next, Figure 4 shows a control device 400 for controlling the electrolyzer cell stack of the electrolyzer in the electrolyzer system.

[0120] The control device 400 includes an input device 402 for receiving input from a sensor 404 to determine the stack operating voltage across the electrolyzer cell stack, the inlet temperature at the fluid inlet, and the outlet temperature at the fluid outlet. Thus, the control device includes a voltage monitoring system 406 for determining the stack operating voltage across the electrolyzer cell stack, an inlet temperature monitoring and / or control system 408 for determining the inlet temperature at the fluid inlet, and an outlet temperature monitoring and / or control system 410 for determining the outlet temperature at at least one fluid outlet of the electrolyzer cell stack. These systems may use sensors and data transmission devices or wiring. The control device receives sensor data associated with each of these measurements. A appropriately programmed processor 412 and associated memory 414 are provided to process such inputs.

[0121] The inlet temperature monitoring and / or control system 408 of the control device may include an output device for controlling the temperature of the fluid entering the electrolyzer cell stack at the fluid inlet. A current control system 416 is also provided for controlling the supply of current to the electrolyzer cell stack. As previously mentioned, during normal operation, this is adapted to supply a constant current to the electrolyzer cell stack, but the current can be reduced or turned off to automatically shut down the stack.

[0122] In this way, the controller 400 is adapted to control the electrolyzer cell stack of the electrolyzer in the electrolyzer system in the manner described above with reference to Figure 3.

[0123] Figures 2 and 3 show how this can be done with a single electrolyzer cell stack, but it can also be one of several stacks in the system, each stack equipped with temperature sensors at its input and output, and this control method may be operated independently.

[0124] As described above, the present invention is particularly applicable to electrolyzers in the field of medium-temperature and high-temperature electrolyzer cells. In some embodiments, at least one electrolyzer cell in the stack is a solid oxide type electrolyzer cell, i.e., the electrochemically active region is a solid oxide. Solid oxide type electrolyzer cells (SOECs) typically operate in the temperature range of 400 to 900°C, and in the case of some chemicals, in the temperature range of 400 to 700°C, or more specifically, 450 to 650°C. Such electrolyzer cells may be called medium-temperature solid oxide type electrolyzer cells, or IT-SOECs.

[0125] The present invention also preferably operates in an electrolyzer that converts vapor into hydrogen and oxygen. The advantage of a vapor-based electrolyzer is that, in vapor electrolysis, particularly in medium and high-temperature vapor electrolysis at temperatures above 400°C, the high-temperature environment reduces the power requirements for electrolyzing water molecules from vapor compared to the electrolysis of liquid water, thus enabling efficient hydrogen production. Furthermore, these temperatures result in lower resistance in the cell. Moreover, the higher the temperature, the relatively higher the reactivity with the electrolyzer compared to liquid water. Therefore, the present invention is very well suited for use in solid oxide type electrolyzer cells (or SOECs) operating at temperatures above 400°C (commonly known as medium-temperature SOECs, or high-temperature SOECs when above 750°C).

[0126] Furthermore, as mentioned above, there are many possible forms of SOEC using various electrochemically active electrolyte chemicals. For example, three well-known electrolyte materials are yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), and gadolinium-doped ceria (GDC or CGO).

[0127] Due to the SOEC temperature (usually exceeding 400°C), liquid water passing through the electrolyzer cell evaporates into high-temperature steam. However, a fluid temperature control system, which controls the temperature of the fluid entering the electrolyzer cell stack, typically ensures that the liquid water is already converted to superheated steam before entering the stack.

[0128] Alternatively, in some embodiments, the electrolyzer cell system comprises high-temperature electrolyzer cells with a stack operating temperature of 750°C to 1100°C.

[0129] As briefly mentioned above, instead of steam and water, carbon dioxide may be used as the fuel, and instead of hydrogen and oxygen, carbon monoxide and oxygen may be produced.

[0130] The present invention is described above merely as an example. Further modifications to the present invention can be made within the scope of the appended claims.

Claims

1. A method for controlling the electrolyzer cell stack of an electrolyzer in an electrolyzer system, The electrolyzer cell stack comprises a fluid inlet and one or more fluid outlets, The electrolyzer system is A fluid temperature control system for controlling the temperature of the fluid entering the electrolyzer cell stack at the fluid inlet, A current control system for controlling the supply of current to the electrolyzer cell stack, A voltage monitoring system for determining the stack operating voltage across the electrolyzer cell stack, An inlet temperature monitoring and / or control system for determining the inlet temperature at the fluid inlet, An outlet temperature monitoring and / or control system for determining the outlet temperature at at least one of the one or more fluid outlets, The method includes, The current supply to the electrolyzer cell stack is controlled to a fixed input current, The temperature delta is calculated by subtracting the determined inlet temperature from the determined outlet temperature, Includes, i) If the absolute value of the temperature delta is greater than the threshold, the following formula applies: T ｎｅｗ =T ｏｌｄ +(dT×TΔ) Here, T ｎｅｗ This is the adjusted target input temperature. T ｏｌｄ This is the current (target) input temperature. dT is an adjustment factor that is less than 1 and greater than zero. TΔ is the calculated temperature delta. A method comprising adjusting the inlet temperature using

2. ii) If the absolute value of the temperature delta is lower than the threshold, Determining the operating voltage across the electrolyzer cell stack, The operating state of the stack is determined based on whether the determined operating voltage is below a voltage threshold, The method according to claim 1, including the method described in claim 1.

3. The method according to any one of the claims, wherein the electrolyzer comprises more than one stack.

4. The method according to claim 3, wherein the method is applied individually to each stack.

5. The method according to any one of the claims, wherein the operation voltage across the electrolyzer cell stack is determined by a voltage sensor, and the output temperature at the fluid outlet is determined periodically at predetermined time intervals.

6. The method according to any one of the claims, wherein the temperature delta threshold is set to a value within the range of 1 to 5°C.

7. The method according to any one of the claims, wherein the temperature delta includes an offset.

8. The method according to any one of the claims, wherein the method also monitors the output fluid in order to check the target gas output volume or percentage from the stack.

9. The method according to any one of the claims, wherein the electrolyzer cell stack is a medium-temperature or high-temperature electrolyzer cell stack.

10. The method according to any one of the claims, wherein the electrolyzer cell stack is a solid oxide type electrolyzer cell stack.

11. The method according to any one of the claims, wherein the electrolyzer is a vapor electrolyzer.

12. The method according to any one of the claims, comprising issuing a warning or shutting down the stack if the determined operating state of the stack is a potential runaway state, or both.

13. The method according to any one of the claims, as dependent on claim 2, wherein the voltage threshold relates to the optimal voltage for achieving a thermoneutral condition at a given temperature.

14. The method according to claim 13, wherein the voltage threshold is the value obtained by subtracting a predefined delta from the optimal voltage.

15. The method according to any one of the claims, further comprising setting a maximum inlet temperature threshold and switching the operating mode from constant current to constant potential when the inlet temperature reaches the maximum inlet temperature threshold.

16. A control device for controlling the electrolyzer cell stack of an electrolyzer in an electrolyzer system, A fluid temperature control system for controlling the temperature of the fluid entering the electrolyzer cell stack at the fluid inlet of the electrolyzer cell stack, A current control system for controlling the supply of current to the electrolyzer cell stack, A voltage monitoring system for determining the stack operating voltage across the electrolyzer cell stack, An inlet temperature monitoring and / or control system for determining the inlet temperature at the fluid inlet, An outlet temperature monitoring and / or control system for determining the outlet temperature at at least one fluid outlet of the electrolyzer cell stack, Equipped with, The current supply to the electrolyzer cell stack is controlled to a fixed input current. The temperature delta is calculated by subtracting the determined inlet temperature from the determined outlet temperature. Adapted to, If the absolute value of the temperature delta is greater than the threshold, then the following equation applies: T ｎｅｗ =T ｏｌｄ +(dT×TΔ) Here, T ｎｅｗ This is the adjusted target input temperature. T ｏｌｄ This is the current (target) input temperature. dT is an adjustment factor that is less than 1 and greater than zero. TΔ is the calculated temperature delta. A control device further adapted to adjust the inlet temperature using the following:

17. The control device according to claim 16, further adapted to determine an operating voltage across the electrolyzer cell stack if the absolute value of the temperature delta is lower than a threshold, and to determine the operating state of the stack depending on whether the determined operating voltage is below a voltage threshold.

18. A control device according to claim 16 or 17, further configured to perform the method described in any one of claims 1 to 15.

19. A computer program that includes instructions causing a computer to perform a step of the method according to any one of claims 1 to 15 when the program is executed by the computer.

20. A non-temporary computer-readable medium containing instructions that, when executed by a processor, perform steps of the method according to any one of claims 1 to 15.

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