Patent Application
20240133065
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2021-067897, filed on Apr. 13, 2021, and International Patent Application No. PCT/JP2021/047525, filed on Dec. 22, 2021, the entire content of each of which is incorporated herein by reference.
The present invention relates to a device for supporting deterioration determination, a device for water electrolysis, and a method for supporting deterioration determination.
In recent years, renewable energy obtained by wind power, sunlight, or the like has attracted attention as energy capable of suppressing carbon dioxide emission in the generation process as compared with energy obtained by thermal power generation. The power generated from the renewable energy is accumulated by a stationary energy storage system, whereby the output power can be smoothed. In recent years, as the stationary energy storage system, water electrolysis modules for producing hydrogen gas by electrolysis of water have been widely used. As the water electrolysis module, for example, as disclosed in Patent Literature 1, a solid polymer water electrolysis module, an alkaline water electrolysis module, a solid oxide water electrolysis module, and the like are known.
In general, a water electrolysis module, which is a component of a device for water electrolysis, tends to deteriorate due to an influence of operation time, temperature, the number of times of starting and stopping, and the like, and hydrogen production efficiency thereof tends to gradually decrease. In order to exhibit a stable function as an energy storage system, it is desirable to grasp the deterioration state of the water electrolysis module. On the other hand, a decrease in hydrogen gas production efficiency can be led by switching the normal operation of the water electrolysis module to an operation for deterioration determination in order to grasp the deterioration state of the water electrolysis module. Therefore, it is required to grasp the deterioration state while continuing the normal operation state of the water electrolysis module. However, since the reaction conditions can change every second during the normal operation, it is difficult to determine the deterioration of the water electrolysis module.
The present invention has been made in view of such a situation, and an object of the present invention is to provide a technique to support deterioration determination for a water electrolysis module during normal operation.
An aspect of the present invention is a device for supporting deterioration determination. The device includes: a first calculating unit that: acquires a dataset including a plurality of reaction condition values and a voltage each of which is measured, or derived from a value measured, in a first period and in a second period after the first period and related to a water electrolysis reaction in a water electrolysis module; and uses the dataset and a predetermined calculation formula to calculate a parameter group of the calculation formula for each period; a second calculating unit that substitutes a predetermined reaction condition value in the calculation formula in which the parameter group is incorporated to calculate a comparison target value for each period; and a third calculating unit that calculates a deterioration degree of the water electrolysis module based on a difference between: a first comparison target value calculated from the calculation formula in which the parameter group in the first period is incorporated; and a second comparison target value calculated from the calculation formula in which the parameter group in the second period is incorporated.
Another aspect of the present invention is a device for supporting deterioration determination. The device includes: a first calculating unit that: acquires a dataset including a plurality of reaction condition values and a voltage each of which is measured, or derived from a value measured, in a first period and in a second period after the first period and related to a water electrolysis reaction in a water electrolysis module; and uses the dataset and a predetermined calculation formula to calculate a parameter group of the calculation formula for each period; and a fourth calculating unit that calculates a deterioration degree of the water electrolysis module based on a difference between: at least one coefficient constituting the parameter group in the first period; and the coefficient in the second period.
Another aspect of the present invention is a device for water electrolysis. The system includes: a water electrolysis module; and the device for supporting deterioration determination according to any of the aspects.
Another aspect of the present invention is a method for supporting deterioration determination. The method includes: acquiring a dataset including a plurality of reaction condition values and a voltage each of which is related to a water electrolysis reaction in a water electrolysis module, in a first period and in a second period after the first period; using the dataset and a predetermined calculation formula to calculate a parameter group of the calculation formula for each period; substituting a predetermined reaction condition value in the calculation formula in which the parameter group is incorporated to calculate a comparison target value for each period; and calculating a deterioration degree of the water electrolysis module based on a difference between: a first comparison target value calculated from the calculation formula in which the parameter group in the first period is incorporated; and a second comparison target value calculated from the calculation formula in which the parameter group in the second period is incorporated.
Any combination of the above components and any modification of the expressions of the present disclosure among methods, apparatuses, systems, and the like are also effective as an aspect of the present disclosure.
Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:
Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. The embodiments are not intended to limit the technical scope of the present invention but are examples, and all features described in the embodiments and combinations thereof are not necessarily essential to the invention. Therefore, the contents of the embodiments can be subjected to many design changes such as changes, additions, and deletions of components without departing from the spirit of the invention defined in the claims. A new embodiment to which a design change is made has the effect of each of the combined embodiments and the modifications. In the embodiments, the contents capable of such a design change are emphasized with notations such as “of the present embodiment” and “in the present embodiment”, but the design change is allowed even in the contents without such notations. Any combination of the above components is also effective as an aspect of the present invention.
The same or equivalent components, members, and processes illustrated in the drawings are denoted by the same sign, and redundant descriptions will be omitted as appropriate. In addition, the scale and shape of each part illustrated in each drawing are set for convenience in order to facilitate descriptions, and are not limitedly interpreted unless otherwise specified. In addition, when the terms “first”, “second”, and the like are used in the present specification or claims, the terms do not represent any order or importance, but are used to distinguish one configuration from another. In addition, in each drawing, some members that are not important for describing the embodiment are omitted.
The water electrolysis module 2 is an electrolyzer that generates hydrogen by electrolysis of water. The water electrolysis module 2 according to the present embodiment is a solid polymer membrane type device for water electrolysis using a solid ion exchange membrane. The water electrolysis module 2 includes an oxygen generating electrode 12, an oxygen generating electrode chamber 14, a hydrogen generating electrode 16, a hydrogen generating electrode chamber 18, and a membrane 20.
The oxygen generating electrode 12 is an electrode where an oxidation reaction occurs and is defined as a positive electrode (anode). The oxygen generating electrode 12 includes a catalyst layer 12a and a gas diffusion layer 12b. The catalyst layer 12a contains, for example, iridium (Ir) or platinum (Pt) as a catalyst. The catalyst layer 12a may contain other metals or metal compounds. The catalyst layer 12a is disposed in contact with one main surface of the membrane 20. The gas diffusion layer 12b is formed of a conductive porous body or the like. As a material constituting the gas diffusion layer 12b, a known material can be used. The oxygen generating electrode 12 is equipped in the oxygen generating electrode chamber 14. The space excluding the oxygen generating electrode 12 in the oxygen generating electrode chamber 14 constitutes a flow path of water and oxygen.
The hydrogen generating electrode 16 is an electrode where a reduction reaction occurs and is defined as a negative electrode (cathode). The hydrogen generating electrode 16 includes a catalyst layer 16a and a gas diffusion layer 16b. The catalyst layer 16a contains, for example, platinum as a catalyst. The catalyst layer 16a may contain other metals or metal compounds. The catalyst layer 16a is disposed in contact with the other main surface of the membrane 20. The gas diffusion layer 16b is formed of a conductive porous body or the like. As a material constituting the gas diffusion layer 16b, a known material can be used. The hydrogen generating electrode 16 is equipped in the hydrogen generating electrode chamber 18. The space excluding the hydrogen generating electrode 16 in the hydrogen generating electrode chamber 18 constitutes a flow path of water and hydrogen.
The oxygen generating electrode 12 and the hydrogen generating electrode 16 are separated by the membrane 20. The membrane 20 is disposed between the oxygen generating electrode 12 and the hydrogen generating electrode 16. The membrane 20 of the present embodiment is composed of a proton exchange membrane (PEM), which is one type of solid polymer membrane. The PEM is not particularly limited as long as it is a material through which protons (H+) conduct, and examples thereof include a fluorine-based ion exchange membrane having a sulfonate group.
The reaction during water electrolysis in the water electrolysis module 2 is as follows.
2H2O→O2+4H++4e− Anodic reaction during electrolysis:
4H++4e−→2H2 Cathodic reaction during electrolysis:
On the oxygen generating electrode 12, water is electrolyzed to generate oxygen gas, protons, and electrons. The protons move through the membrane 20 toward the hydrogen generating electrode 16. The electrons flow into the positive electrode of the power supply 4. The oxygen gas is discharged to the outside through the oxygen generating electrode chamber 14. On the hydrogen generating electrode 16, hydrogen gas is generated by a reaction between electrons supplied from the negative electrode of the power supply 4 and protons having moved through the membrane 20. The hydrogen gas is discharged to the outside through the hydrogen generating electrode chamber 18.
The power supply 4 is a DC power supply that supplies power to the water electrolysis module 2. When power is supplied from the power supply 4 to the water electrolysis module 2, a predetermined electrolysis voltage is applied between the oxygen generating electrode 12 and the hydrogen generating electrode 16 of the water electrolysis module 2, and an electrolysis current flows. The power supply 4 is supplied with power from a power supply apparatus 21 and supplies power to the water electrolysis module 2. The power supply apparatus 21 of the present embodiment is constituted with a power generation apparatus that generates power using renewable energy, for example, a wind power generation apparatus 22, a solar power generation apparatus 24, or the like. Note that the power supply apparatus 21 is not limited to a power generation apparatus using renewable energy, and may be a system power supply, a power storage apparatus storing power from a renewable energy power generation apparatus or a system power supply, or the like. In addition, a combination of two or more thereof may be used.
The first supply mechanism 6 supplies water to the oxygen generating electrode chamber 14. The first supply mechanism 6 includes a first circulation tank 26, a first circulation path 28, and a first circulation device 30. The first circulation tank 26 stores water that is supplied to the oxygen generating electrode chamber 14 and recovered from the oxygen generating electrode chamber 14. For example, the first circulation tank 26 stores pure water.
The first circulation tank 26 and the oxygen generating electrode chamber 14 are connected through the first circulation path 28. The first circulation path 28 includes a forward path portion 28a to supply water from the first circulation tank 26 to the oxygen generating electrode chamber 14, and a return path portion 28b to recover water from the oxygen generating electrode chamber 14 to the first circulation tank 26. The first circulation device 30 is provided, for example, in the middle of the forward path portion 28a. By driving the first circulation device 30, water flows in the first circulation path 28 and circulates between the first circulation tank 26 and the oxygen generating electrode chamber 14. As the first circulation device 30, for example, various pumps such as a gear pump and a cylinder pump, a natural flow type device, and the like can be used.
The first circulation tank 26 also functions as a gas-liquid separator. Since oxygen is generated by the electrode reaction on the oxygen generating electrode 12, the water recovered from the oxygen generating electrode chamber 14 contains gaseous oxygen and dissolved oxygen. The gaseous oxygen is separated from the water in the first circulation tank 26 and taken out of the system. The water from which oxygen is separated is supplied to the water electrolysis module 2 again. A gas-liquid separator may be provided separately from the first circulation tank 26.
The second supply mechanism 8 supplies water to the hydrogen generating electrode chamber 18. The second supply mechanism 8 includes a second circulation tank 32, a second circulation path 34, and a second circulation device 36. The second circulation tank 32 stores water that is supplied to the hydrogen generating electrode chamber 18 and recovered from the hydrogen generating electrode chamber 18. For example, the second circulation tank 32 stores pure water.
The second circulation tank 32 and the hydrogen generating electrode chamber 18 are connected through the second circulation path 34. The second circulation path 34 includes a forward path portion 34a to supply water from the second circulation tank 32 to the hydrogen generating electrode chamber 18, and a return path portion 34b to recover water from the hydrogen generating electrode chamber 18 to the second circulation tank 32. The second circulation device 36 is provided, for example, in the middle of the forward path portion 34a. By driving the second circulation device 36, water flows in the second circulation path 34 and circulates between the second circulation tank 32 and the hydrogen generating electrode chamber 18. As the second circulation device 36, for example, various pumps such as a gear pump and a cylinder pump, a natural flow type device, and the like can be used.
The second circulation tank 32 also functions as a gas-liquid separator. Since hydrogen is generated by the electrode reaction on the hydrogen generating electrode 16, the water recovered from the hydrogen generating electrode chamber 18 contains gaseous hydrogen and dissolved hydrogen. The gaseous hydrogen is separated from the water in the second circulation tank 32 and taken out of the system. The water from which hydrogen is separated is supplied to the water electrolysis module 2 again. A gas-liquid separator may be provided separately from the second circulation tank 32.
The structure of the device 1 for water electrolysis is not limited to that described above. For example, the water electrolysis module 2 may be anion exchange membrane (AEM) type, alkaline type, solid oxide type, or the like. When the water electrolysis module 2 is PEM type, the second supply mechanism 8 can be omitted. In this case, a pipe to take out hydrogen gas to the outside of the system is connected to the hydrogen generating electrode chamber 18. It may be a configuration in which water is not returned from the oxygen generating electrode chamber 14 to the first circulation tank 26 but sent from the oxygen generating electrode chamber 14 to the outside of the system. The water electrolysis module 2 may also include a plurality of cells or a plurality of stacks. In this case, as an example, each of the cells or each of the stacks are arranged in the same direction such that the oxygen generating electrode chamber 14 and the hydrogen generating electrode chamber 18 are arranged in the same direction, and are stacked with an energizing plate interposed between the adjacent cells or stacks. As a result, each of the cells or each of the stacks are electrically connected in series. The energizing plate is made of a conductive material such as metal.
The control device 10 controls the operation of the device 1 for water electrolysis. The control device 10 is realized by an element or a circuit such as a CPU or a memory for computers as the hardware configuration, and is realized by a computer program or the like as the software configuration, and is illustrated as functional blocks realized by cooperation thereof in
Values of various reaction conditions related to the water electrolysis reaction in the water electrolysis module 2 are input to the control device 10 from a sensor 38 provided in the device 1 for water electrolysis. The sensor 38 repeatedly measures values of various reaction conditions at a predetermined timing, and sends measurement results to the control device 10. The control device 10 or the device 40 for supporting deterioration determination described later holds the acquired measurement results in the memory. If necessary, the control device 10 or the device 40 for supporting deterioration determination derives a reaction condition value from the value measured by the sensor 38. The reaction conditions related to the water electrolysis reaction include voltage, current, water temperature, oxygen gas pressure, hydrogen gas pressure, and the like. Hereinafter, in the present disclosure, the values excluding the voltage among these are referred to as “reaction condition value”. In addition, the reaction condition value and the voltage are collectively referred to as “dataset”.
For example, the sensor 38 includes a known voltmeter, measures the potential of the oxygen generating electrode 12 and the hydrogen generating electrode 16 or the voltage of the water electrolysis module 2 (so-called stack voltage or cell voltage), and sends them to the control device 10. The potential of each electrode and the voltage of the water electrolysis module 2 can be detected by a known method. For example, when the sensor 38 detects the potential of each electrode, a reference electrode is provided on the membrane 20. The reference electrode is held at the reference electrode potential. For example, the reference electrode is a reversible hydrogen electrode (RHE). Then, one terminal of the voltmeter is connected to the reference electrode, and the other terminal is connected to the electrode to be detected, and the potential of the electrode with respect to the reference electrode is detected. In addition, when the sensor 38 detects the voltage of the water electrolysis module 2, one terminal of the voltmeter is connected to the oxygen generating electrode 12 and the other terminal is connected to the hydrogen generating electrode 16, and the potential difference between both electrodes, that is, the voltage, is detected. When the sensor 38 detects the voltage, the reference electrode can be omitted.
The sensor 38 includes a known ammeter, measures an electric current that flows between the oxygen generating electrode 12 and the hydrogen generating electrode 16, and sends the measurement value to the control device 10. The sensor 38 includes a known thermometer, measures the temperature of water flowing through the water electrolysis module 2, and sends the measurement value to the control device 10. The temperature of water flowing through the water electrolysis module 2 may be fictitiously determined by, for example, the temperature of water in the first supply mechanism 6 such as in the first circulation tank 26, the temperature of water in the second supply mechanism 8 such as in the second circulation tank 32, or an average value thereof.
In addition, the sensor 38 includes a known pressure gauge, measures the pressure of oxygen gas and hydrogen gas generated in the water electrolysis module 2, and sends the measurement values to the control device 10. The pressure of oxygen gas generated in the water electrolysis module 2 is, for example, the pressure of oxygen gas in the oxygen generating electrode chamber 14. The pressure of hydrogen gas generated in the water electrolysis module 2 is, for example, the pressure of hydrogen gas in the hydrogen generating electrode chamber 18.
The control device 10 controls the output of the power supply 4, the driving of the first supply mechanism 6 and the second supply mechanism 8, and the like on the basis of measurement results of the sensor 38. In addition, the control device 10 includes a device 40 for supporting deterioration determination. The device 40 for supporting deterioration determination is realized, in the same manner as the control device 10, by an element or a circuit such as a CPU or a memory for computers as the hardware configuration, and is realized by a computer program or the like as the software configuration, and is illustrated as functional blocks realized by cooperation thereof in
The device 40 for supporting deterioration determination acquires a dataset including a plurality of reaction condition values and a voltage each of which is related to the water electrolysis reaction by using the sensor 38 or the like, and obtains a parameter group by using these datasets and a predetermined calculation formula. A predetermined reaction condition value is substituted into the calculation formula in which this parameter group is incorporated to obtain a comparison target value. The deterioration degree of the water electrolysis module 2 is calculated based on a difference between: a first comparison target value calculated from the calculation formula in which the parameter group in a first period is incorporated; and a second comparison target value calculated from the calculation formula in which the parameter group in a second period after the first period is incorporated. The calculated deterioration degree can be used as an index for determining the deterioration state of the water electrolysis module 2. The predetermined reaction condition value can be appropriately set based on experiments, simulations, and the like. The device 40 for supporting deterioration determination includes a first calculating unit 42, a second calculating unit 44, a third calculating unit 46, a notification unit 48, and a driving support unit 50.
The first calculating unit 42 acquires a dataset including a plurality of reaction condition values and a voltage each of which is measured with the sensor 38 or derived from a value measured therewith. Thereafter, the parameter group is calculated by using the dataset and the predetermined calculation formula.
First, a voltage calculation formula is defined in advance as the predetermined calculation formula. The defined calculation formula is stored in the device 40 for supporting deterioration determination. The calculation formula stored in the device 40 for supporting deterioration determination may be rewritable from the outside. The device 40 for supporting deterioration determination may define the voltage calculation formula.
Therefore, the voltage calculation formula can be expressed as the equation (1). Hereinafter, a voltage calculated by the voltage calculation formula is referred to as a calculated voltage Vsim.
Vsim=u+ηact+ηIR (1)
In the equation (1), only the anodic reaction is considered. In addition, resistance loss caused by components other than the membrane 20 and concentration overvoltage are ignored. The voltage calculation formula may be added with an activation overvoltage term ηact_H2 of the hydrogen generation reaction, a concentration overvoltage term ηconc, a temperature correction term (a difference between the water temperature at the time of circulation and the water temperature at the time of electrode reaction), and the like.
The equilibrium potential u of the water electrolysis reaction can be calculated by, for example, the equation (2), that is, Nernst's equation.
In the equation (2), “1.23” is an equilibrium potential (theoretical electrolytic potential) in the standard state (1 atm and 25° C. in the present disclosure). a is a constant, for example, 0.009. T is the absolute temperature of water flowing through the water electrolysis module 2. “298.15” is the absolute temperature of water in the standard state. R is a gas constant. F is Faraday constant. P_H2 is the pressure of hydrogen gas generated from the water electrolysis module 2. P_O2 is the pressure of oxygen gas generated from the water electrolysis module 2. P_H2O is the saturated vapor pressure of water in the water electrolysis module 2. That is, the equilibrium potential u is calculated by the function of the absolute temperature T of water, the pressure P_H2 of hydrogen gas, the pressure P_O2 of oxygen gas, and the saturated vapor pressure P_H2O of water.
T, P_H2, and P_O2 correspond to a reaction condition value measured by the sensor 38. P_H2O corresponds to a reaction condition value derived from these reaction condition values. The equilibrium potential u may be calculated using a function of other measured values. The equilibrium potential u may be calculated by the equation (3), which ignores the pressure term, or may be a constant as shown in the equation (4).
u=1.23−a(T−298.15) (3)
u=1.23 (4)
The activation overvoltage ηact of the oxygen generation reaction can be calculated, for example, from the equation (5).
ηact=f(T,i) (5)
In the equation (5), T is the absolute temperature of water flowing through the water electrolysis module 2. i is a current density flowing through the water electrolysis module 2. That is, the activation overvoltage ηact is an estimated value calculated by the function f of the absolute temperature T of water and the current density i. The current density i is calculated from a current value measured by the sensor 38. The activation overvoltage ηact may be calculated using a function of other measured values or may be a constant.
An example of the function f for calculating the activation overvoltage ηact is a function based on Butler-Volmer equation. The activation overvoltage ηact can be calculated from the equation (6).
In the equation (6), R is a gas constant. T is the absolute temperature of water flowing through the water electrolysis module 2. α is a charge transfer coefficient. F is Faraday constant. arsinh is an inverse hyperbolic function. i is a current density. i0 is an exchange current density. Eexc is the activation energy of electron transfer. α, i0, and Eexc are a coefficient, and can be a component of the parameter group described later. In addition, they can be corrected through a method such as a curve fitting method conducted by the least squares method described later. Note that literature data may be substituted for α, i0, and Eexc.
Another example of the function f for calculating the activation overvoltage ηact is a function based on Tafel equation. The activation overvoltage ηact can be calculated from the equation (7).
In the equation (7), R is a gas constant. T is the absolute temperature of water flowing through the water electrolysis module 2. α is a charge transfer coefficient. F is Faraday constant. i is a current density. i0 is an exchange current density.
The resistance overvoltage ηIR can be calculated, for example, from the equation (8).
ηIR=r(T)i (8)
In the equation (8), r is a resistance value of the membrane 20, T is the absolute temperature of water flowing through the water electrolysis module 2, and i is a current density flowing through the water electrolysis module 2. That is, the resistance overvoltage ηIR is an estimated value calculated based on the resistance value r, which is a function of the absolute temperature T of water, and the current density i. In defining the function of the resistance value r, other measured values may be used, or a constant may be used.
Examples of the equation (8), which calculates the resistance overvoltage ηIR, include the equation (9).
In the equation (9), δ is the thickness of the membrane 20. σ is the proton conductivity of the membrane 20. i is a current density. Epro is a proton transfer activation energy. R is a gas constant. T is the absolute temperature of water flowing through the water electrolysis module 2. σ and Epro are a coefficient, and can be a component of the parameter group described later. In addition, they can be corrected through a method such as a curve fitting method conducted by the least squares method described later. Note that literature data may be substituted for σ and Epro.
The denominator on the right side in the equation (9) represents a proton conductivity, which contributes to the membrane resistance. In the equation (9), the portion is represented by Arrhenius equation, but can be represented by the formula (10) as another example.
In the formula (10), a, b, and c are unique coefficients determined according to the material of the membrane 20 and the like. When the material of the membrane 20 is unknown and the values of a, b, and c cannot be specified, these coefficients can be a component of the parameter group described later. In addition, λ represents the water content of the membrane 20. λ is a coefficient, and can be a component of the parameter group described later. In addition, a, b, c, and λ can be corrected through a method such as a curve fitting method conducted by the least squares method described later. Note that literature data may be substituted for a, b, c, and λ.
In addition, the resistance overvoltage ηIR can also be expressed as the equation (11) with the resistance value r as a constant independent of temperature.
ηIR=r×i (11)
In the equation (11), i is a current density. r is the resistance value of the membrane 20 and is a constant. The resistance value r is determined by actual measurement or the like.
The first calculating unit 42 acquires a plurality of datasets for each period from output values of the sensor 38. This dataset includes, as components, various reaction condition values to be substituted into the calculation formula and a measurement voltage Vobs measured by the sensor 38. Since the above-described voltage calculation formula is used in the present embodiment, examples of the reaction condition values include current, water temperature, hydrogen generation pressure, oxygen generation pressure, and the like. The first calculating unit 42 calculates the calculated voltage Vsim by substituting the reaction condition values in a plurality of datasets into the voltage calculation formula, and corrects the parameter group so that the calculated voltage Vsim is close to the measurement voltage Vobs.
In the present embodiment, the first period is a period where the water electrolysis module 2 presumably has not been deteriorated. This makes it possible to more precisely determine the life of the water electrolysis module 2. For example, a predetermined period immediately after the water electrolysis module 2 starts to be used can be presumed as the period where the water electrolysis module 2 has not been deteriorated. The period where the water electrolysis module 2 has not been deteriorated can be appropriately set based on experiments, simulations, and the like. The second period is a period where the water electrolysis module 2 is intended to be measured for its deterioration state.
Coefficients in each of the calculation formulas may change as the water electrolysis module 2 deteriorates. That is, since the coefficient in the calculation formula is a physical property value for each configuration of the water electrolysis module 2, the appropriate value can change according to the state of the water electrolysis module 2. For each period, the first calculating unit 42 corrects the coefficients included in each calculation formula so that the calculation voltage Vsim is close to the measurement voltage Vobs. The correction is only required to be performed on at least one coefficient. Specifically, when, for example, the equation (6) is used for the term of the activation overvoltage ηact, any one of α, i0, and Eexc may be corrected, the rest being substituted with a literature data. Specifically, when, for example, the formula (9) is used for the term of the resistance overvoltage ηIR, any one of σ and Epro may be corrected, the rest being substituted with a literature data. When a coefficient is calculated in the first period, a literature data may be used as the initial value of the coefficient.
For example, the dataset acquired in each period includes a combination of reaction condition values at a plurality of times and the measurement voltage Vobs at the times. The first calculating unit 42 corrects the coefficient of the voltage calculation formula using the combination of a plurality of reaction condition values and the measurement voltages Vobs. The correction of the coefficient can be performed by a known correction method such as curve fitting by the least squares method. As a result, the first calculating unit 42 calculates a parameter group including the corrected coefficient as a component for each period. When only some coefficients are corrected, the parameter group also includes coefficients as literature data or the like.
The second calculating unit 44 substitutes a predetermined reaction condition value into each of two calculation formulas in which the parameter group in each period is incorporated, thereby calculating a comparison target value for each period. The predetermined reaction condition value is not a value included in the dataset but a value that can be appropriately set based on an experiment, simulation, or the like. Examples of the comparison target value include the calculated voltage Vsim, the activation overvoltage ηact, and the resistance overvoltage ηIR.
The third calculating unit 46 calculates a deterioration degree based on a difference between: a first comparison target value calculated from the calculation formula in which the parameter group in the first period is incorporated; and a second comparison target value calculated from the calculation formula in which the parameter group in the second period is incorporated. This deterioration degree corresponds to the progress of the deterioration state of the water electrolysis module 2 in the second period based on the deterioration state of the water electrolysis module 2 in the first period. As another embodiment, without using the comparison target value, the fourth calculating unit (not illustrated) may calculate a deterioration degree by directly comparing at least one of the coefficients constituting the parameter group for each period with each other.
When the calculated voltage Vsim is used as the comparison target value, a calculated voltage Vsim1 is calculated from the calculation formula in which the parameter group in the first period is incorporated. In addition, a calculated voltage Vsim2 is calculated from the calculation formula in which the parameter group in the second period is incorporated. Then, a first deterioration degree d1 is calculated based on the difference between the two calculated voltages Vsim.
Specifically, the second calculating unit 44 substitutes a predetermined reaction condition value into the voltage calculation formula in which the parameter group in the first period is incorporated to calculate the calculated voltage Vsim1. In addition, the voltage calculation formula in which the parameter group in the second period is incorporated is substituted with the same reaction condition value, thereby the calculated voltage Vsim2 is calculated. Then, the third calculating unit 46 calculates the first deterioration degree d1 using, for example, the formula (12).
d1=(Vsim2−Vsim1)/Vsim1 (12)
In addition, the second calculating unit 44 of the present embodiment calculates an activation overvoltage ηact1 in the first period and an activation overvoltage ηact2 in the second period using the parameter group in each period. The third calculating unit 46 calculates a second deterioration degree d2 of the water electrolysis module 2 based on the difference between the two activation overvoltages ηact.
Specifically, the second calculating unit 44 substitutes a predetermined reaction condition value into the term of the activation overvoltage ηact in the voltage calculation formula in which the parameter group in the first period is incorporated to calculate the activation overvoltage ηact1. In addition, the term of the activation overvoltage ηact in the voltage calculation formula in which the parameter group in the second period is incorporated is substituted with the same predetermined reaction condition value, thereby the activation overvoltage ηact2 is calculated. Then, the third calculating unit 46 calculates the second deterioration degree d2 using, for example, the formula (13).
d2=(ηact2−ηact1)/ηact1 (13)
The deterioration state of the catalyst layer 12a of the oxygen generating electrode 12 can be determined by calculating the second deterioration degree d2 as described above. Therefore, the deterioration state of the water electrolysis module 2 can be estimated in more detail.
In addition, the second calculating unit 44 of the present embodiment calculates a resistance overvoltage ηIR1 in the first period and a resistance overvoltage ηIR2 in the second period using the parameter group in each period. The third calculating unit 46 calculates a third deterioration degree d3 of the water electrolysis module 2 based on the difference between the two resistance overvoltages ηIR.
Specifically, the second calculating unit 44 substitutes a predetermined reaction condition value into the term of the resistance overvoltage ηIR in the voltage calculation formula in which the parameter group in the first period is incorporated to calculate the resistance overvoltage ηIR1. The term of the resistance overvoltage ηIR in the voltage calculation formula in which the parameter group in the second period is incorporated is substituted with the same reaction condition value, thereby the resistance overvoltage ηIR2 is calculated. Then, the third calculating unit 46 calculates the third deterioration degree d3 using, for example, the formula (14).
d3=(ηIR2−ηIR1)/ηIR1 (14)
The deterioration state of the membrane 20 can be determined by calculating the third deterioration degree d3 as described above. Therefore, the deterioration state of the water electrolysis module 2 can be estimated in more detail.
The third calculating unit 46 can quantitatively determine the progress of deterioration of the water electrolysis module 2 based on each of the first deterioration degree d1, the second deterioration degree d2, and the third deterioration degree d3, based on a combination of two or more, or based on both. For example, for each of the first deterioration degree d1 to the third deterioration degree d3, threshold values d10 to d30 for deterioration degree to give a standard whether or not the water electrolysis module 2 should be replaced are set in advance and stored in the device 40 for supporting deterioration determination. The threshold values d10 to d30 can be appropriately set based on experiments, simulations, and the like. The third calculating unit 46 can calculate remaining life td of the water electrolysis module 2, in other words, the replacement time of the water electrolysis module 2, using the formula (15).
In the formula (15), t1 is a time at the center of the first period. t2 is a time at the center of the second period.
The notification unit 48 notifies the user that the replacement time of the water electrolysis module 2 has come when at least one of the first deterioration degree d1 to the third deterioration degree d3 exceeds the threshold. The notification method is not particularly limited, and a known method such as generating a notification sound and lighting a notification lamp can be adopted. The notification unit 48 may notify the user when two or more of the first deterioration degree d1 to the third deterioration degree d3 exceed the threshold, or when all the deterioration degrees exceed the threshold. When the device 1 for water electrolysis includes a plurality of the water electrolysis modules 2, the first deterioration degree d1 to the third deterioration degree d3 for each water electrolysis module 2 can be calculated to individually determine the replacement time of each water electrolysis module 2. The notification unit 48 can be omitted.
The driving support unit 50 compares the ratio (d2/d20) of the second deterioration degree d2 to the threshold value d20 with the ratio (d3/d30) of the third deterioration degree d3 to the threshold value d30. For example, in the case of d2/d20>d3/d30, the control device 10 is given an instruction on operating conditions to avoid operation causing deterioration of the catalyst layer 12a of the oxygen generating electrode 12. For example, in the case of d3/d30>d2/d20, the control device 10 is given an instruction on operating conditions to avoid operation causing deterioration of the membrane 20. A constant C may be added to the ratio (d3/d30) of the third deterioration degree d3 to the threshold value d30 to obtain d3/d30+C. Thus, the life of the water electrolysis module 2 can be prolonged. The operation method for suppressing deterioration of the catalyst layer 12a or the membrane 20 can be appropriately set based on experiments, simulations, and the like. The driving support unit 50 can be omitted.
Next, a dataset in the first period is acquired (S103). The dataset is provided by the sensor 38. If a calculation formula is defined (Y in S101), the calculation formula-defining process is skipped, and the dataset in the first period is acquired. Subsequently, a parameter group in the first period is calculated using the defined calculation formula and the acquired dataset (S104). The parameter group in the first period is provided by the device 40 for supporting deterioration determination. The fact that the first period has been reached, in other words, the calculation timing of the parameter group in the first period may be given as an instruction by the user or the like from the outside, or may be given by a program set in advance in the device 40 for supporting deterioration determination.
Subsequently, it is determined whether the second period, in which the deterioration state of the water electrolysis module 2 is desired to be measured, has been reached (S105). If the second period has not been reached (N in S105), the determination process (S105) as to whether the second period has been reached is repeated. If the second period is reached (Y in S105), a dataset in the second period is acquired (S106). The dataset is provided by the sensor 38 and the device 40 for supporting deterioration determination. Subsequently, a parameter group in the second period is calculated using the defined calculation formula and the acquired dataset (S107). The parameter group in the second period is provided by the device 40 for supporting deterioration determination. The fact that the second period has been reached, in other words, the calculation timing of the parameter group in the second period may be given as an instruction by the user or the like from the outside, or may be given by a program set in advance in the device 40 for supporting deterioration determination.
Subsequently, the first comparison target value and the second comparison target value are calculated using the calculation formula in which the parameter group in the first period is incorporated and the calculation formula in which the parameter group in the second period is incorporated (S108). Then, the deterioration degree of the water electrolysis module 2 is calculated based on the difference between the first comparison target value and the second comparison target value (S109). The deterioration degree is provided by the device 40 for supporting deterioration determination. The calculated deterioration degree is notified to the user. Accordingly, the user can grasp the replacement time of the water electrolysis module 2. Further, operation control of the water electrolysis module 2 according to the deterioration degree is executed.
Subsequently, it is determined whether the water electrolysis module 2 has been replaced (S110). If the water electrolysis module 2 has been replaced (Y in S110), this flow ends. Then, the flow of the method for supporting deterioration determination is newly executed for the replaced water electrolysis module 2. In the new flow, the calculation formula defined in the previous flow is diverted (Y in S101). Note that the calculation formula may be redefined for each execution of the flow, or may be redefined at an arbitrary timing. If the water electrolysis module 2 has not been replaced (N in S110), the process of determining whether the second period has been reached (S105) to the process of calculating deterioration degree (S109) are repeated. The water electrolysis module 2 is replaced by the user. The device 40 for supporting deterioration determination determines whether or not replacement is performed.
As described above, the device 1 for water electrolysis according to the present embodiment includes the water electrolysis module 2 and the device 40 for supporting deterioration determination. The device 40 for supporting deterioration determination includes the first calculating unit 42, the second calculating unit 44, and the third calculating unit 46.
According to the present embodiment, the progressively deteriorated water electrolysis module 2 is quickly replaced and the operation state is controlled according to the degree of deterioration, which can stabilize the water electrolysis module in hydrogen production efficiency to stabilize the function as an energy storage system. The deterioration of the water electrolysis module 2 can be grasped based on the electrolysis voltage, which increases along with the deterioration. Therefore, in conventional deterioration determination methods, the reaction conditions (temperature and current) of the water electrolysis module 2 are fixed to specific conditions, and the deterioration is determined from the voltage at that time. However, the operation of measuring the voltage while fixing the reaction conditions of the water electrolysis module 2 is different from the operation during the normal operation of the water electrolysis module 2, which may prevent the water electrolysis module 2 from producing hydrogen. Therefore, a method for determining the deterioration of the water electrolysis module 2 without disturbing normal operation of the water electrolysis module 2 is desired.
In contrast, in the present embodiment, a dataset during normal operation of the water electrolysis module 2 is acquired over time. This dataset includes a reaction condition value to be substituted into the calculation formula and the measurement voltage Vobs to be used for correcting the coefficient. Subsequently, the coefficient included in each calculation formula is corrected so that the calculated voltage Vsim obtained by substituting the reaction condition value into the calculation formula is close to the measurement voltage Vobs, and the parameter group in each period is obtained. Subsequently, the first comparison target value and the second comparison target value are calculated using the parameter group in the first period and the parameter group in the second period. Then, the deterioration degree of the water electrolysis module 2 is calculated based on the difference between the first comparison target value and the second comparison target value.
The comparison target value calculated by the above-described method includes information on the deterioration state of the water electrolysis module 2 in the period. The comparison target value does not depend on the operating condition of the water electrolysis module 2. Therefore, it is possible to more precisely estimate the deterioration state of the water electrolysis module 2 while keeping the normal operation of the water electrolysis module 2 without performing a special operation for deterioration determination. Therefore, the device 40 for supporting deterioration determination and the method for supporting deterioration determination according to the present embodiment can support the deterioration determination of the water electrolysis module 2 during the normal operation. In addition, since the replacement time of the water electrolysis module 2 can be more precisely grasped, an increase in labor and cost due to unnecessary replacement can be suppressed.
The water electrolysis module 2 of the present embodiment includes the oxygen generating electrode 12, the hydrogen generating electrode 16, and the membrane 20 separating these electrodes. The calculation formula used for calculating the parameter group is a formula for calculating the calculated voltage Vsim by adding the equilibrium potential u of the water electrolysis reaction, the activation overvoltage ηact of the oxygen generating reaction, and the resistance overvoltage ηIR of the membrane 20.
The embodiments may be identified by the items described below.
A device (40) for supporting deterioration determination, the device including:
The device (40) for supporting deterioration determination according to item 1, wherein
The device (40) for supporting deterioration determination according to item 2, wherein
A device (40) for supporting deterioration determination, the device including:
The device (40) for supporting deterioration determination according to any one of items 1 to 4,
A device (1) for water electrolysis, comprising:
A method for supporting deterioration determination, the method including:
A renewable energy fluctuation absorbing system including the device (1) for water electrolysis according to item 6.
A maintenance system for a water electrolysis module (2), the maintenance system including:
A driving support system for a water electrolysis module (2), the driving support system including:
Hereinafter, Examples of the present invention will be described, but Examples are merely an example for suitably describing the present invention, and do not limit the present invention at all.
A water electrolysis operation test was performed for 3 days using a PEM type water electrolysis module of 3 Nm3/h.
In the voltage calculation formula, the equation (6) was used for the term of the activation overvoltage ηact. Among the coefficients related to the activation overvoltage ηact, the coefficient to be corrected was the exchange current density i0. For the charge transfer coefficient α and the activation energy of electron transfer Eexc, literature data were substituted, which means α=0.7, and Eexc=53,000 J/mol. The equation (9) was used for the term of the resistance overvoltage ηIR. Among the coefficients related to the resistance overvoltage ηIR, the coefficient to be corrected was the proton conductivity σ. For the proton transfer activation energy Epro, literature data was substituted, which means Epro=10,000 J/mol.
Predetermined reaction condition values were substituted in the voltage calculation formula in which the generated parameter group for each period was incorporated, thereby calculating the voltage Vsim (V1_ST,sim), the activation overvoltage ηact (V2_ST,sim), and the resistance overvoltage ηIR (V3_ST,sim) in each period. A current of 1200 A, a water temperature of 30° C., a hydrogen generation pressure of 0.6 MPaG, and an oxygen generation pressure of 0.595 MPaG were substituted for the predetermined reaction condition values. The first deterioration degree d1, the second deterioration degree d2, and the third deterioration degree d3 were calculated based on the obtained calculated voltage Vsim, activation overvoltage ηact, and resistance overvoltage ηIR. The results are shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-067897 | Apr 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/047525 | 12/22/2021 | WO |
