Electrochemical apparatus

Abstract

The electrochemical apparatus includes at least one electrochemical cell, two fluid lines, a preheating unit for preheating at least one fluid before supplying at least one fluid to the system, a load element for electrically loading at least one electrochemical cell, a temperature sensor, and a pressure sensor for detecting pressure and / or pressure difference. The apparatus includes a control management system. The control management system is configured to maintain a temperature gradient between the inlet and outlet of at least one fluid line below a predetermined system critical temperature gradient and / or to control the minimum and / or maximum temperatures of the entire electrochemical apparatus relative to a predetermined reference temperature, and / or to control the pressure difference between two fluid lines, and / or to control the pressure drop of at least one fluid line, and / or to control at least one maximum and / or at least one minimum pressure of the fluid in the electrochemical apparatus relative to a predetermined reference pressure.

Description

Technical Field

[0001] The present invention relates to an electrochemical device described in the preamble of the independent claim and a method for controlling the electrochemical device.

Background Art

[0002] Controlling the reaction fluid in an electrochemical reactor such as a fuel cell is common. Controlling the pressure difference of the fluid flowing through the reactor is important to prevent failure of components within the electrochemical reactor due to the pressure difference and / or the mixing flow of the fluid flowing through the reactor.

[0003] The pressure difference can be adjusted passively, for example, using a diaphragm, a liquid, a spool valve, an elastic tube, a rigid partition arranged between bellows, or an expansion body / contraction body communicating with one or both of the reactant lines. The advantage of such passive control is, in principle, that it does not require any control logic. As a potential drawback, such passive control may be impossible or undesirable in some applications because it essentially minimizes the pressure difference between the reactants. Therefore, in certain applications, the pressure difference is actively controlled, for example, using a combination of a control valve, a pressure gauge, and specific control logic.

[0004] JP2002-373682A describes controlling the pressure difference of a fuel cell system using an adjustment valve that adjusts the pressure difference between a fuel supply line and an oxidant supply line.

[0005] Also, JP4606038B2 discloses maintaining the outlet oxidant at a low pressure using a controllable oxidant exhaust valve. A similar method is also disclosed in EP2108199B1.

[0006] Specific situations in which exhaust pressure difference control is preferred include when the exhaust flow is used for recycling purposes, as disclosed in EP3432399B1, or when the exhaust flow is supplied to a device located downstream of the reactor for additional fluid processing purposes, to generate an additional pressure drop in the fluid or to generate an attractive force on the outlet side of the reactor, as disclosed in US10727508B2, EP3841635A1, and US2021 / 399318A1.

[0007] Furthermore, it is recognized that feedback from the stack can contribute to improving pressure difference control. EP2075866B1 describes improving the accuracy of the pressure difference based on feedback from the stack voltage and feedback from the leak detection unit. Similar methods are disclosed in JP5231847B2 and EP3432399B1.

[0008] Furthermore, DE102008010711B4 discloses a method for controlling the pressure difference in reactant supply lines by controlling the mass flow rate of each reactant supply line using control logic. This couples the pressure of the fuel-containing fluid and the oxygen-containing fluid so that a change in the mass flow rate of at least one gas does not affect the gas pressure of that gas.

[0009] The above solutions are usually sufficient for electrochemical reactors operating at low temperatures. In contrast, electrochemical reactors operating at high temperatures, such as those based on solid oxide electrochemical cells, also rely on controlling the reactants to maintain the temperature gradient within the reactor within acceptable limits. Such control can be achieved by preheating at least one of the fluids supplied to the reactor. For example, such control can be achieved by preheating an oxygen-containing fluid. In reactors intended to generate electricity from fuel, the oxygen-containing fluid provides an oxidizing agent, electrochemically oxidizing the fuel-containing fluid. In reactors that use electricity to produce a fuel-containing fluid, the oxygen-containing fluid is often used as a sweeping gas to remove oxygen gas produced, for example, at an oxygen electrode.

[0010] Information regarding the effect of thermal gradients on thermal stress in high-temperature electrochemical stacks is described, for example, in WO2021 / 083625A1. This suggests that materials subjected to tensile stress are particularly at risk.

[0011] It has been reported in the literature that the temperature gradient of reactors employing solid oxide batteries is 5–10°C / cm. Exceeding these temperature limits can cause mechanical failure due to the thermomechanical properties of the electroceramics used in the batteries. The reason why it is difficult to protect the temperature limits is that while the temperature gradient may exist in any component of the battery, the control strategy usually relies on information from a limited number of sensors located outside the reactor rather than within the reactor itself.

[0012] When a system is in a transient state, transitioning from one operating state to another, precise control of reactants and heat in a high-temperature reactor becomes more complex, while at the same time, it is necessary to optimally maintain electrical efficiency, thermal efficiency, reactant conversion rate, or electrical losses related to the fluids flowing through the reactor.

[0013] Another problem arises if the electrolyte layer used in high-temperature electrochemical reactors is not completely airtight. This can occur when low-cost, easily scaled-up manufacturing techniques are used and defect rates are kept low.

[0014] When oxygen-containing fluids mix with fuel-containing fluids, two problems arise. Firstly, oxygen present in the fuel-containing fluid can irreversibly degrade the electrolytic catalysts responsible for the electrochemical conversion reactions of the fuel-containing fluid, as well as the catalysts in electrochemical cells involved in gas conversion reactions such as water-gas reforming or conversion reactions.

[0015] Secondly, the presence of oxygen in the fuel-containing fluid can degrade the quality of the fuel-containing fluid discharged from the electrochemical battery. This is due not only to the introduction of oxidizers in the fuel-containing fluid, which can cause irreversible damage to the fuel electrodes, but also to the introduction of other chemical elements present in the oxygen-containing fluid (nitrogen, if air is used). For example, if the exhaust flow of the fuel-containing fluid is recycled to the battery inlet for the purpose of high system efficiency, or if there are specific requirements regarding the chemical composition of the exhaust flow of the fuel-containing fluid that is being processed in an electrochemical battery located downstream of the electrochemical battery, such as a hydrogen purification battery or a hydrogen pressurization battery, or used in a catalytic reactor to produce ammonia from nitrogen and hydrogen flows, then altering the fuel-containing fluid by mixing it with an oxygen-containing fluid is particularly undesirable.

[0016] No control method has been proposed to address all of the above-mentioned problems. [Overview of the Initiative] [Problems that the invention aims to solve]

[0017] Therefore, at least one object of the present invention is to overcome the shortcomings of the prior art. At least one object is to provide an electrochemical apparatus with improved control of reactant flow and temperature. Another object of the present invention is to provide a method for controlling an electrochemical apparatus. [Means for solving the problem]

[0018] These objectives are achieved by the subject matter of the independent claims. Preferred embodiments are described with respect to the dependent claims.

[0019] A first aspect of the present invention relates to an electrochemical apparatus. The electrochemical apparatus is An electrochemical cell comprising an anode, a cathode, and a membrane, It comprises two fluid lines, including a fuel supply line and an oxygen supply line, each line including an inlet for supplying fluid to the system and an outlet for removing the treated fluid from the system. A preheating unit for preheating at least one of the fluids before supplying it to the system, A load element for electrically loading at least one electrochemical cell, A temperature sensor for detecting at least one of the fluid inlet temperature and the fluid outlet temperature, The system includes pressure sensors for detecting pressure and / or pressure difference, particularly preferably maximum or minimum pressure relative to a known reference pressure.

[0020] The device further includes a control and management system. The control system is configured to maintain the temperature gradient between the inlet and outlet of at least one fluid line below a predetermined system critical temperature gradient, and / or to control the minimum and / or maximum temperatures of the entire electrochemical apparatus relative to a predetermined reference temperature.

[0021] The term "critical temperature" refers to a temperature at which prolonged operation could cause damage or mechanical failure to the device, and may be a temperature specific to the device.

[0022] Furthermore, the control and management system may be configured to maintain the temperature gradient between the inlet and outlet of both fluid lines below a predetermined critical temperature.

[0023] Additionally or alternatively, the control system is configured to control the pressure difference between the two fluid lines such that the fuel supply line is overpressurized relative to the oxygen supply line. Thus, the pressure can be controlled across the entire battery membrane. The pressure difference is preferably maintained within a preset range, for example, 2 millibars to 30 millibars. In this case, the pressure of the fuel-containing fluid is overpressurized relative to the pressure of the oxygen-containing fluid.

[0024] Additionally or alternatively, the control management system is configured to control the pressure drop of at least one fluid line, preferably both fluid lines, of the electrochemical reactor such that the pressure at the inlet is higher than the pressure at the outlet, and preferably maintain the pressure drop of at least one fluid within a preset range. The preset range is preferably from 0 to 650 millibars. In this way, the losses associated with the fluid flowing through the electrochemical reactor are maintained within an acceptable range.

[0025] Also, the term "pressure drop" means "the pressure difference between the fluid inlet and the fluid outlet", which is different from the pressure difference between two fluid lines.

[0026] Additionally or alternatively, the control management is configured to control at least one maximum pressure and / or at least one minimum pressure of the fluid within the electrochemical device with respect to a predetermined reference pressure. The predetermined reference pressure may be the ambient pressure, for example, the standard pressure of 1 bar. Also, the predetermined pressure may be the pressure within a container within the device. Preferably, at least one maximum pressure and / or at least one minimum pressure is maintained within a preset range. For example, when the reference pressure is the standard pressure of 1 bar, the minimum pressure may be set higher than 1 bar. The maximum pressure may be set, for example, at a level where the reactor can be safely operated or at a level that does not pose an operational risk to the environment, for example, 5 bar.

[0027] The above-described device is particularly useful when the fuel-containing fluid discharged from the electrochemical cell is further processed downstream or recirculated towards the inlet of the electrochemical reactor.

[0028] The term "fluid" refers to a liquid or a gas, particularly a gas. The fluid can function as a reactant for generating fuel. Also, for example, in the case of a solid oxide electrolyzer, the fluid may be a sweep gas for removing oxygen generated from the system.

[0029] An electrochemical cell, especially in the case of multiple electrochemical cells, may also be called an electrochemical reactor or simply a reactor. The electrochemical reactor may be a high-temperature electrochemical reactor, preferably a solid oxide cell reactor.

[0030] The oxidizer supply line may contain oxygen in addition to other components. For example, the oxidizer supply line may contain air. The fuel supply line may contain fuel gases such as hydrogen or carbon monoxide and other gases such as water vapor or carbon dioxide.

[0031] The control and management system may be configured to prioritize internal pressure difference limits and / or maximum and / or minimum pressure limits over temperature gradient limits in order to exceed the temperature gradient limit.

[0032] For example, the temperature gradient within the electrochemical reactor is preferably maintained below 75°C. Therefore, the risk of failure of internal components of the electrochemical reactor is reduced. This is demonstrated by model calculations considering local temperature calculations as a function of the maximum electrolyte defect size expected throughout the operating life, as a function of the local pressure difference between the two reaction flows, and is supported by experimental observations. The temperature gradient within the electrochemical reactor is within an acceptable range to prevent harmful failures of the electrochemical cell. If the temperature gradient exceeds this limit, in order to comply with the pressure difference limit, the temperature gradient may rise, for example, to 100°C, at which point corrective measures must be taken until the temperature gradient reaches a maximum of 75°C, while maintaining the pressure difference limit. The maximum temperature limit may be 100°C during a temporary overshoot. Therefore, in a particular case, the optimal value is 75°C as described above, with a 25°C overshoot being possible.

[0033] Surprisingly, it was found that exceeding the temperature gradient limit to comply with the pressure difference limit allowed the system to operate more safely and effectively prevented irreversible degradation of equipment components. This was because it took into account not only the overall temperature and pressure gradient, but also gas crossover in the reactor due to the inevitable presence of hot spots.

[0034] A device employing the proposed control method may include the following elements: The apparatus may include at least one flow controller located in at least one fluid line. The flow controller is connected to or connectable to a control system for controlling the mass flow rate of the fluid. To control the mass flow rate of all fluids, flow controllers may be located in all fluid lines.

[0035] Additionally or alternatively, the apparatus may include a pressure sensor for measuring the pressure in a fluid line, a pressure difference sensor for measuring the pressure difference between fluid lines, or a pressure sensor for measuring the pressure in a fluid line relative to ambient pressure.

[0036] Additionally or alternatively, the apparatus may include a temperature sensor for measuring the temperature of at least one fluid.

[0037] Additionally or alternatively, the apparatus may include sensors for analyzing the composition of at least one fluid entering or leaving the reactor.

[0038] If the device includes a sufficient number of sensors, it may be appropriately controlled by, for example, one or more hysteresis loops. These hysteresis loops can function independently, sequentially, or in a cascaded manner. In the cascaded manner, one hysteresis loop receives feedback from another hysteresis loop.

[0039] Advantageously, the mass flow rate and preheating temperature during fluid operation are based on lookup tables, thermodynamic models that calculate the heat balance according to imposed operating conditions, real-time optimization routines, or data-driven models. This reduces the number of sensors required to control the pressure and pressure difference within the electrochemical reactor.

[0040] For example, data about the current state of the system can be obtained from sensors, and this data can be correlated into a lookup table or model, allowing for adjustment of the operating mass flow rate and preheating temperature to ensure the safe operation of the electrochemical apparatus.

[0041] During operation, the pressure drop in an electrochemical reactor with a planar electrochemical cell is directly proportional to the mass flow rate and kinematic viscosity (i.e., the internal resistance of the fluid to fluid flow under gravity). Kinematic viscosity is proportional to pressure, proportional to the 3 / 2 power of absolute temperature, and depends on the fluid composition. Based on this relationship, one or more lookup tables can be constructed from which the operating mass flow rate and preheating temperature of a target fluid can be determined. The accuracy of at least one lookup table depends on the level of detail included in the calculation. For example, in a simplified state, at least one lookup table may depend on the pressure and temperature measured at the inlet and outlet of the electrochemical stack. In a more advanced state, at least one lookup table may depend, for example, on the average mass flow rate, pressure, and temperature present inside the electrochemical reactor. These depend on the operating state of the reactor, e.g., the rate of fluid conversion by electrochemical reactions occurring during operation, the Joule heat associated with these electrochemical reactions, the heat capacity of the solid materials in the electrochemical stack, the specific heat capacity of the fluid, and the change in fluid composition from inlet to outlet.

[0042] Advantageously, the mass flow rate and preheating temperature during fluid operation are based on an electrochemical or thermomechanical model. Such models can calculate the fluid distribution, the fluid's associated composition and pressure, the temperature distribution inside the electrochemical reactor, and the thermomechanical stresses associated with the material, using operational data provided to the electrochemical reactor and data feedback from the reactor. This allows for a more accurate assessment of the pressure, pressure difference, and temperature inside the electrochemical reactor, enabling more precise monitoring of operational limitations.

[0043] Advantageously, the mass flow rate and preheating temperature during operation are based on real-time optimization routines. In particular, approaches using dynamic models and constraint adaptation are considered practical for real-time control.

[0044] Advantageously, the operating mass flow rate and preheating temperature are based on data-driven models such as artificial neural networks. Once trained using input and output data from physical models or past experimental studies, such data-driven models can estimate the output of the device in response to actual input data without requiring physical equations.

[0045] To predict the performance of an apparatus under conditions where the temperature gradient limit is exceeded while adhering to the pressure difference limit, the apparatus can be trained using data from a physical model that can accurately predict the behavior of the apparatus under those conditions, or the apparatus can be trained using data previously obtained from a representative apparatus that has been tested under those conditions.

[0046] During operation, the pressure drop in the electrochemical reactor is directly correlated with the mass flow rate and kinematic viscosity of the fluid. For example, the pressure drop may be proportional to or unproportionate to the mass flow rate and kinematic viscosity of the fluid.

[0047] Furthermore, it should be understood that the number of sensors that can be reduced using advanced control methods varies from case to case.

[0048] Even with advanced monitoring and control routines, it should be understood that the reactor's response may change during equipment operation and require manual monitoring.

[0049] Preferably, the electrochemical battery is an electrolytic battery or a fuel cell. The electrochemical battery may also be a proton exchange membrane battery, a solid oxide battery, an alkaline battery, or a molten carbonate battery. More preferably, the electrochemical battery is a battery that operates at high temperatures, such as a solid oxide battery or a molten carbonate battery. Even more preferably, an electrochemical reactor employing one or more electrochemical batteries may employ batteries having electrolytes that are not completely airtight, such as a solid oxide battery having a thin film electrolyte thinner than 20 μm, or a battery having an electrolyte that is prone to mechanical failure.

[0050] A pressure control valve can be placed in at least one fluid line, preferably before or after the electrochemical reactor. Alternatively, pressure control valves can be placed in both fluid lines. The pressure control valve can assist or support reliable operation of the pressure control.

[0051] For example, a controllable back pressure valve can be placed at the outlet of a fluid line or in an electrochemical reactor. In this case, the pressure of the fluid involved is controlled in accordance with the pressure drop at both ends of the electrochemical reactor.

[0052] The oxygen supply line may contain an oxygen-containing gas, preferably air. Preferably, an oxygen-containing gas is supplied to the line.

[0053] The present invention is not limited to the above description and can be applied to different configurations. For example, a system employing a preferred control method can classify electrochemical batteries based on their airtightness or tendency for mechanical failure of the electrolyte, and design the battery or group of batteries exhibiting the lowest airtightness or highest failure risk to be used in locations with the lowest risk of, for example, nickel oxidation or oxygen electrode degradation. Such configurations are possible, for example, in systems including stacks operating in cascades, systems including stacks operating at different temperatures, or in stacks where multiple electrochemical batteries, for example two or four batteries, are integrated into each stack repeating element.

[0054] A second aspect of the present invention relates to a method for controlling the electrochemical apparatus described above. The method of the present invention is: a) A step of preheating at least one fluid, b) The step of supplying at least one fluid, preferably two fluids, to an electrochemical cell, c) The procedure includes measuring the inlet temperature of the fluid at the inlet of at least one fluid line and the outlet temperature of the fluid at the outlet of at least one fluid line, maintaining the resulting temperature gradient below a predetermined critical temperature gradient, and / or controlling the minimum and / or maximum temperatures of the electrochemical apparatus with respect to a predetermined temperature or temperature gradient criterion.

[0055] In addition to or instead of step c), the method of the present invention may include the step of measuring the pressure difference between the fuel supply line and the oxygen supply line and adjusting the pressure difference so that the fuel supply line is overpressurized relative to the oxygen supply line.

[0056] In addition to or instead of steps c) and / or d), the method of the present invention may include the steps of e) measuring the pressure drop of at least one fluid flowing through an electrochemical reactor and adjusting the pressure drop so that the inlet pressure is higher than the outlet pressure and / or measuring the maximum and / or minimum pressure of the entire electrochemical cell relative to a predetermined reference pressure and adjusting the pressure to a predetermined range.

[0057] The term reference pressure can refer to the ambient pressure of the device. Alternatively, the reference pressure may be the internal pressure of the device's vessel, or the internal pressure of another component of the device, such as a fluid line or pipe.

[0058] The method of the present invention can significantly reduce failures caused by excessive pressure by controlling the proper function of the device.

[0059] The method of the present invention is applicable to an electrochemical battery, which is a fuel cell. Furthermore, the method of the present invention is applicable to a battery or electrochemical reactor with reversed polarity. In this case, the fuel is produced by electricity or by any other operation involving the conversion of fluids (especially reactants), an operation in which mixing should be kept as low as possible.

[0060] Advantageously, the process includes, after at least one of steps a) to e), preferably one of steps c) to d), determining pressure drop limits and / or maximum pressure limits and / or minimum pressure limits and temperature gradient limits within and / or between fluid lines, and prioritizing the pressure difference limit to exceed the temperature gradient limit, which is typical in steady-state operation.

[0061] For example, during a temporary overshoot, the maximum temperature gradient limit is 100°C. Therefore, the optimal temperature gradient limit is 75°C, allowing for an overshoot of 25°C.

[0062] During steady-state operation, the pressure difference can be changed to comply with the temperature gradient limits for steady-state operation.

[0063] In relation to the heat balance within the reactor, the temperature gradient can be kept lower than a predetermined system temperature gradient by controlling the mass flow rate and preheating temperature of at least one fluid.

[0064] Preferably, the mass flow rate and preheating of at least one fluid during operation are based on a lookup table, or a thermodynamic model that calculates the heat balance according to imposed operating conditions, or a real-time optimization routine, or a data-driven model.

[0065] During operation, the pressure drop in the electrochemical reactor directly correlates with the mass flow rate and kinematic viscosity of the fluid.

[0066] A third aspect of the present invention relates to the use of the aforementioned electrochemical system for generating electricity and / or reactants and / or heat.

[0067] The present invention will be described in more detail based on the following drawings and graphs. The drawings and graphs show a solid oxide electrolytic device operating with air and a hydrogen-water vapor mixture when a 10-micron defect is present in the electrolyte. The drawings and graphs should not be understood as limiting. [Brief explanation of the drawing]

[0068] [Figure 1] Figure 1A shows the hydrogen partial pressure at the reactor inlet when the fuel overpressure is 20 millibars in the nickel oxidation risk assessment, Figure 1B shows the hydrogen partial pressure at the reactor inlet when the pressure difference is 0 millibars in the nickel oxidation risk assessment, and Figure 1C shows the hydrogen partial pressure at the reactor inlet when the air overpressure is 20 millibars in the nickel oxidation risk assessment. [Figure 2] Figure 2A shows the partial oxygen pressure at the outlet when the fuel overpressure is 20 millibars in the oxygen electrode reduction risk assessment, Figure 2B shows the partial oxygen pressure at the outlet when the pressure difference is 0 millibars, and Figure 2C shows the partial oxygen pressure at the outlet when the air overpressure is 20 millibars in the oxygen electrode reduction risk assessment. [Figure 3] Figure 3A shows the water vapor concentration at the outlet when the air overpressure is 20 millibars, and Figure 3B shows the water vapor concentration at the outlet when the pressure difference is 0 millibars. [Figure 4] Figure 4A shows the effect of gas mixing on the outlet temperature when the pressure difference is +20 millibars, and Figure 4B shows the effect of gas mixing on the outlet temperature when the pressure difference is -20 millibars. [Figure 5]Figure 5A shows the current flowing through the electrochemical reactor, Figure 5B shows the temperature difference within the electrochemical reactor, Figure 5C shows the process air flow supplied to the electrochemical reactor, and Figure 5D shows the pressure difference between the fuel electrode and the oxygen electrode (positive values ​​indicate that the fuel is overpressurized relative to the air, and negative values ​​indicate that the air is overpressurized relative to the fuel). [Modes for carrying out the invention]

[0069] To explain the effects of pressure differences in high-temperature electrochemical monocells or stacks using solid oxide batteries, 2D model calculations were performed to evaluate the effects of pressure differences on the oxidation risk of the fuel electrode and the temperature distribution. As input to the model, leakage rate data of fuel electrode / electrolyte half-cells, including metallic nickel electrodes obtained by pre-reducing the fuel electrode, and material analysis information to evaluate the size of defects causing leakage, as well as the porosity and curvature of the fuel electrode (4) and oxygen electrode (3), were obtained experimentally. This model estimated the flow rate through pinholes, the gas distribution through porous layers, and the temperature distribution within the associated porous structure (2), considering Stefan-Maxwell diffusion and Knudsen diffusion.

[0070] In the analysis, the pressure difference between +20 millibars (overpressurized fuel electrode) and -20 millibars (overpressurized oxygen electrode), and the defect size of the membrane (1) ranging from 1 to 10 microns were examined.

[0071] a) Risk of nickel oxidation To assess the risk of nickel oxidation, we investigated conditions in which the reaction fluid temperature was set to 770°C, 10% hydrogen and 90% water vapor were supplied to the fuel electrode (4), and air was supplied to the oxygen electrode (3), near a defect (2) in the electrolyte (1) where the fluid could enter from one electrode to the other. Since the fluid at the fuel electrode contains only 10% hydrogen, this case is considered one of the most extreme cases of nickel oxidation.

[0072] Figure 1 shows hydrogen concentrations from 10%, 7%, 1%, to 0% hydrogen when the defect (2) size is 10 microns. A scale for the amount of hydrogen corresponding to the above percentages is provided on the side of each figure. When the pressure difference is +20 millibars (Figure 1A), fuel flows towards the oxygen electrode (3) (upper part of each graph). When the pressure difference is 0 millibars (Figure 1B), air diffuses towards the fuel electrode (4). When the pressure difference is -20 millibars (Figure 1C, the oxygen electrode is overpressurized), air flows towards the fuel electrode (4), and the risk of nickel oxidation is high over a wide range. The risk range is indicated by a hydrogen concentration of approximately 1 volume% in the fuel-air mixture, but nickel oxidation can occur even below that (down to a hydrogen concentration of 1 ppmv).

[0073] Table 1 summarizes the regions where nickel oxidation can occur in all cases examined. These regions are directly adjacent to the electrolyte and where air penetrates most deeply, and are estimated as a function of the pressure difference for different defect sizes. The affected regions were estimated by isobars (images not shown) indicating a 3 vol% hydrogen partial pressure. Within these regions, the hydrogen partial pressure dropped below this value due to air intrusion. From Table 1, it can be seen that the fuel electrode becomes unstable only when the defect size exceeds 2 microns, under both a pressure difference of -10 millibars and a pressure difference of -20 millibars (air overpressure). When the pressure is constant and the fuel overpressure is 1 millibar, the risk of anode oxidation is small for the maximum defect size of 10 microns. For smaller defect sizes and higher fuel overpressures, no risk of nickel oxidation is observed.

[0074] [Table 1]

[0075] In the most extreme cases, where the maximum pressure difference was -20 millibars and +20 millibars (maximum defect of 10 microns), we investigated the effect of gas contamination on temperature. We found that the temperature rise was greatest when air was mixed into the fuel electrode side, with a maximum temperature difference of 13°C in the target flame.

[0076] b) Risk of reduction in oxygen electrodes To assess the risk of reduction of the oxygen electrode, we investigated conditions in which a hydrogen-water vapor mixture was supplied to the fuel electrode (4) and air to the oxygen electrode (2) near a defect (2) in the electrolyte (1) where fluid could enter from one electrode to the other, with the reactor temperature set to 770°C. We assumed that the hydrogen-water vapor mixture was converted into a mixture consisting of 90% hydrogen and 10% water vapor by electrochemical conversion from water vapor to hydrogen. Since the fluid at the fuel electrode contains 90% hydrogen, this case is considered one of the most extreme cases of oxygen electrode reduction.

[0077] Figure 2 shows the oxygen concentration when the defect (2) is 10 microns in size. When the fuel overpressure is 20 millibars (+20 millibars, Figure 2A), it can be seen that fuel flows to the oxygen electrode (3), causing a decrease in the partial pressure of oxygen. When the pressure is equal (0 millibars, Figure 2B), some fuel diffuses to the oxygen electrode (3), while some air diffuses towards the fuel electrode. When the air overpressure is 20 millibars (-20 millibars, Figure 2C), air flows to the fuel electrode (4).

[0078] Table 2 summarizes the region where oxygen electrode reduction can occur in all cases considered. This region is directly adjacent to the electrolyte and where air penetrates most deeply, and is estimated as a function of the pressure difference for different defect sizes. The affected region was estimated by using a graph showing the region where the oxygen partial pressure is less than 10E-5 atm, which is considered the boundary at which the oxygen electrode of solid oxide batteries, such as many mixed conductive perovskites used in LSCFs, becomes irreversibly unstable. From Table 2, it can be seen that the oxygen electrode becomes unstable at a pressure difference of +20 millibars only when the defect size is 10 microns. For smaller defect sizes and lower fuel overpressures, no risk of oxygen electrode reduction is observed.

[0079] [Table 2]

[0080] Figure 3 shows the water vapor concentration when the defect (2) is 10 microns in size. When the fuel overpressure is 20 millibars (+20 millibars, Figure 3A), it can be seen that the water vapor concentration increases to 45% due to the flow of the hydrogen-water vapor mixture to the oxygen electrode (3). The water vapor is formed by the combustion of hydrogen and mixing from the fuel side. When the pressure is constant (0 millibars, Figure 3B), the fuel diffuses to the oxygen electrode (3), but the water vapor concentration at the oxygen electrode (3) is low.

[0081] Water vapor present in oxygen electrodes has been reported to destabilize typical oxygen electrode materials such as LSCF. For example, water vapor in oxygen electrodes may be involved in the elution of strontium cations. However, water vapor is unlikely to destabilize oxygen electrodes to the extent that they become dysfunctional.

[0082] Figure 4 shows the effect of gas contamination on temperature in the most extreme cases, where the maximum pressure difference is +20 millibars (Figure 4A) and -20 millibars (Figure 4B) (where the defect at the electrolytic cell outlet is a maximum of 10 microns). According to Figure 4, the temperature rise was greatest when fuel was mixed into the oxygen electrode (3), with a maximum temperature difference of 43°C relative to the nominal temperature of the target flame of 770°C. This temperature is considerably higher than the temperature difference observed at the electrolytic cell inlet, indicating a correlation between the defect and a large local temperature gradient.

[0083] Therefore, it is thought that the control of the feed flow and its associated temperature and pressure differences is not based solely on the overall temperature and pressure gradients obtained from sensor measurements as the feed flows into and out of the reactor, but more importantly, on the inevitable presence of hot spots due to gas contamination within the reactor. The presence of these hot spots is typically overlooked or ignored in the prior art.

[0084] Table 3 summarizes the temperature overshoot (°C) near the defect for all pressure differences examined. In all cases, a temperature increase was observed, with the highest temperature increase occurring when the maximum fuel overpressure was +20 millibars and the maximum defect size was 10 microns.

[0085] [Table 3]

[0086] Based on the above findings and experimental observations from a solid oxide reactor subjected to a maximum fuel overpressure of 20 millibars at an operating temperature of approximately 750°C, the hypothesis was derived that solid oxide stacks may be more tolerant of temperature gradients during operation than is generally understood from thermal cycling experiments between the operating temperature and ambient temperature. As a result, the inventors proposed and experimentally verified a control scheme that prioritizes pressure difference control over temperature control. This scheme reduces the competition between temperature control and reactant control by allowing the reactor to exceed the temperature gradient limits typical of steady-state operation during system transients while optimally maintaining system performance. This results in the advantage of improved operability of the apparatus.

[0087] c) Application of the present invention The four graphs in Figure 5 illustrate the practical use of the control strategy. From top to bottom, the following parameters are shown for a specific time frame during the operation of the electrochemical reactor: the current flowing through the electrochemical reactor (fuel cell mode or electrolysis mode) (Figure 5A), the temperature difference within the electrochemical reactor, e.g., the difference between the temperature of the outflow fluid and the temperature of the inflow fluid (Figure 5B), the flow rate of process air supplied to the electrochemical reactor (Figure 5C), and the pressure difference between the fuel electrode and the oxygen electrode (positive numbers indicate that the fuel is overpressurized relative to the air, and negative numbers indicate that the air is overpressurized relative to the fuel) (Figure 5D).

[0088] The control strategy is further clarified by four graphs. These graphs consider two cases. First, we describe the reactor response when pressure difference is not prioritized over temperature. This is shown by a curve that becomes dashed when it reaches the second vertical dashed line.

[0089] Next, we will describe the reactor response when pressure difference is prioritized over temperature. This is shown by a curve that remains continuous even after reaching the second or third vertical dashed line.

[0090] In the first case, assuming that the fuel supply to the fuel electrode, the oxygen supply to the oxygen electrode, and the associated temperatures are constant, we can see the reactor's response when the current flowing through the reactor is increased from the initial setpoint to a new setpoint. This is shown by vertical dashed lines 1 and 2.

[0091] Temperature graph 5B shows that the reactor temperature rises because the reactor generates more heat. Due to the reactor's thermal inertia, the reactor generates heat immediately after the current increases.

[0092] To suppress the temperature rise inside the reactor, the airflow is increased using a feedback loop that responds to the reactor temperature, as shown in the third graph 5C. As a result, the air pressure increases and the pressure difference decreases. This causes the air to become overpressurized relative to the fuel (i.e., the pressure difference decreases).

[0093] Once the new current setting (vertical dashed line 2) is reached, it can be freely increased (as shown by vertical dashed line 3) until the airflow stabilizes, and as a result the pressure difference drops further until it falls below the minimum allowable pressure difference, the reactor temperature becomes level.

[0094] In the second case disclosing the proposed control method, the airflow rate is adjusted at the point where the pressure difference reaches the minimum allowable pressure difference (in the graph, this point is reached just before vertical dashed line 2), or at a safety margin (not shown) exceeding the minimum allowable pressure difference. This causes a temperature overshoot.

[0095] To compensate for the reactor temperature, the pressure difference is increased by adjusting the back pressure to a value that allows for a safe increase in airflow, and then the airflow adjustment is released (shown by the shaded beam). This further increases the airflow, and it can be confirmed that the reactor temperature reaches a safe steady temperature. The increased airflow causes another decrease in the pressure difference, but at this point it still reaches a level that adheres to the minimum allowable pressure difference (shown in the graph when it reaches vertical dashed line 4), or a value that maintains a safety margin above the minimum allowable pressure difference (not shown).

Claims

1. An electrochemical apparatus, An electrochemical cell comprising an anode, a cathode, and a membrane, It comprises two fluid lines, including a fuel supply line and an oxygen supply line, each line including an inlet for supplying fluid to the system and an outlet for removing the treated fluid from the system. A preheating unit for preheating at least one of the fluids before supplying it to the system, A load element for electrically loading the at least one electrochemical cell, A temperature sensor for detecting at least one of the fluid inlet temperature and the fluid outlet temperature, It includes a pressure sensor for detecting pressure and / or pressure difference, The aforementioned device includes a control and management system, The aforementioned control management system is It is configured to maintain the temperature gradient between the inlet and outlet of at least one fluid line below a predetermined system critical temperature gradient, and / or to control the minimum and / or maximum temperatures of the entire electrochemical apparatus relative to a predetermined reference temperature, and / or The system is configured to control the pressure difference between the two fluid lines such that the fuel supply line is overpressurized relative to the oxygen supply line, and / or The system is configured to control the pressure drop of at least one fluid line, preferably to maintain the pressure drop of at least one fluid within a preset range, such that the pressure at the inlet is higher than the pressure at the outlet, and / or An electrochemical apparatus, preferably configured to maintain at least one maximum pressure and / or at least one minimum pressure within a preset range, in order to control at least one maximum pressure and / or at least one minimum pressure of the fluid in the electrochemical apparatus with respect to a predetermined reference pressure.

2. The apparatus according to claim 1, wherein the control management system is further configured to take precedence over the pressure difference limit and / or maximum pressure limit and / or minimum pressure limit within the apparatus over the temperature gradient limit, in order to exceed the temperature gradient limit.

3. The apparatus includes at least one flow controller located in at least one fluid line, The apparatus according to claim 1 or 2, wherein the flow controller is connected to or connectable to the control management system for controlling the mass flow rate of the fluid.

4. The apparatus according to any one of the preceding claims, wherein the mass flow rate and preheating temperature of the fluid during operation are based on a lookup table, or on a thermodynamic model that calculates the heat balance according to imposed operating conditions, or on a real-time optimization routine, or on a data-driven model.

5. The apparatus according to any one of the preceding claims, wherein the electrochemical battery is an electrolytic battery or a fuel cell.

6. The apparatus according to any one of the preceding claims, wherein a pressure control valve is located before and / or after the electrochemical reactor.

7. The apparatus according to any one of the preceding claims, wherein the oxygen supply line includes an oxygen-containing gas, preferably air.

8. A method for controlling an electrochemical apparatus according to claims 1 to 7, a) A step of preheating at least one fluid, b) The step of supplying at least one fluid to an electrochemical cell, c) Measuring the inlet temperature of the fluid at the inlet of at least one fluid line and the outlet temperature of the fluid at the outlet of at least one fluid line, and maintaining the resulting temperature gradient below a predetermined critical temperature gradient and / or controlling the minimum and / or maximum temperatures in the electrochemical apparatus with respect to a predetermined temperature or temperature gradient criterion, and / or d) Measuring the pressure difference between the fuel supply line and the oxygen supply line, and adjusting the pressure difference so that the fuel supply line is overpressurized relative to the oxygen supply line, and / or e) A method comprising the steps of measuring a pressure drop of at least one fluid in the entire electrochemical reactor and adjusting the pressure drop such that the pressure at the inlet is higher than the pressure at the outlet, and / or measuring the maximum and / or minimum pressure of the entire electrochemical cell relative to a predetermined reference pressure and adjusting the pressure to a predetermined range.

9. The method according to claim 8, further comprising, after at least one of steps a) to e), determining pressure drop limits and / or maximum pressure limits and / or minimum pressure limits and temperature gradient limits within and / or between fluid lines, and prioritizing the pressure difference limit to exceed the temperature gradient limit.

10. The method according to claim 9, wherein the maximum temperature gradient limit during a temporary overshoot is 100°C.

11. The method according to claims 8 to 10, wherein the pressure difference is changed during steady-state operation in order to comply with the temperature gradient limit of the steady-state operation.

12. The method according to claims 8 to 11, wherein the temperature gradient is kept lower than a predetermined system temperature gradient by controlling the mass flow rate and preheating temperature of at least one fluid.

13. The method according to claim 12, wherein the mass flow rate and preheating of the at least one fluid during operation are based on a lookup table, or on a thermodynamic model that calculates the heat balance according to imposed operating conditions, or on a real-time optimization routine, or on a data-driven model.

14. Use of the electrochemical system according to claims 1 to 7 for the generation of electricity and / or reactants and / or heat.

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