Method for operating an electrochemical system

Abstract

The invention relates to a method for operating an electrochemical system which comprises a plurality of electrochemical stacks (11; 12; 13; 21; 22; 23; 31; 32; 33) that are electrically and / or hydraulically interconnected. The following steps are carried out: - detecting at least one state parameter of each stack (11; 12; 13; 21; 22; 23; 31; 32; 33), - determining a degree of degradation of each stack (11; 12; 13; 21; 22; 23; 31; 32; 33) using the detected state parameters, - outputting a recommendation for replacing at least one stack (11; 12; 13; 21; 22; 23; 31; 32; 33) depending on the degree of degradation of the stack, wherein the recommendation comprises a degree-of-degradation range that the new stack (11; 12; 13; 21; 22; 23; 31; 32; 33) to be installed should have and a point in time at which the replacement should take place.

Description

[0001] R. 414398

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for operating an electrochemical plant

[0006] The invention relates to a method for operating an electrochemical plant comprising a plurality of electrochemical stacks, and a method for operating an electrochemical plant comprising a plurality of modules, each with several stacks.

[0007] State of the art

[0008] Electrochemical systems are known from the prior art, for example, for the production of hydrogen and oxygen by the electrolytic splitting of water. Such systems comprise at least one electrochemical stack with a plurality of electrochemical cells in which the actual electrochemical reaction takes place. Within each electrochemical cell, two reaction chambers are formed, separated from each other by a semipermeable membrane or another semipermeable barrier. Depending on the type, at least one of the two reaction chambers is filled with water or an aqueous electrolyte solution. An electrical voltage is applied between the reaction chambers, in each of which an electrode is arranged, thereby electrolytically splitting water, with hydrogen being formed in one reaction chamber and oxygen in the other. The reaction gases are removed from the stack and used for further purposes.stored until further use. Such an electrochemical plant is known, for example, from DE 10 2021 214 205 A1.

[0009] The semipermeable membrane of individual electrochemical cells is permeable to certain ions and largely impermeable to all other substances. In so-called PEM electrolyzers, the membrane is permeable only to protons, i.e., IT-Io- R. 414398

[0010] - 2 - ions are permeable, while all other ions cannot pass through the membrane. The membrane is coated with a catalytic layer where the water in the anode compartment, which forms one of the reaction chambers, is split. Driven by the electrical voltage, the IT ions pass through the membrane and recombine in the cathode compartment to form hydrogen gas. The O₂ remaining in the anode compartment... 2The hydrogen ions recombine there to form oxygen gas. For the chemical reaction to proceed, an electrical voltage greater than approximately 1.5 volts and a current corresponding to the desired hydrogen production rate must be applied between the electrodes of the reaction chambers.

[0011] The stack is subject to aging, meaning that the hydrogen production rate and the parameters for optimal stack operation change over time. Essentially, the stack ages due to two processes:

[0012] Firstly, the membrane thins over time because the semipermeable membrane consists of polymers that are subject to aging. Besides its function of allowing only certain ions to pass through, the membrane also serves to reliably seal the two reaction chambers against each other, despite a sometimes considerable pressure difference between them. Due to the membrane thinning, the maximum operating pressure in the cathode chamber must therefore be reduced over time to ensure the membrane remains stable.

[0013] Secondly, the catalytic coating degrades, resulting in reduced efficiency and the need to increase the cell voltage. Furthermore, the minimum operating temperature must then be raised, which also leads to a reduction in startup dynamics.

[0014] To ensure that stacks can still be operated effectively even with a certain degree of degradation, the operating parameters, especially the applied voltage and the pressures within the stack, must be adjusted throughout the stack's lifetime. In larger modules comprising multiple stacks, the stacks are electrically and / or hydraulically interconnected and supplied with water or electrolytic solution and electricity via common lines. If the stacks age with different R. 414398

[0015] - 3 -

[0016] At higher speeds, the entire module can no longer be operated optimally, as it is no longer possible to control each stack with its optimal parameters. This reduces the efficiency of the entire electrochemical plant and thus increases the cost of hydrogen production.

[0017] Advantages of the invention

[0018] The inventive method for operating an electrochemical plant has the advantage that even with progressive degradation of the stacks, largely optimal operation of the electrochemical plant is enabled, thus keeping the efficiency and therefore the costs of hydrogen production or the production of other chemical substances low. Furthermore, the service life of the entire electrochemical plant can be extended in this way. The inventive method for operating the electrochemical plant, which comprises several electrochemical stacks, involves the following steps:

[0019] Capture at least one state parameter of each stack;

[0020] Determining the degradation level of each stack using the captured state parameters,

[0021] Issuing a recommendation to replace at least one stack depending on the degradation level of the stack, wherein the recommendation includes a degradation range that the new stack(s) to be installed should have, and a time at which the replacement should take place.

[0022] State parameters are physical quantities that characterize the state of a stack. Such state parameters can include, for example, the temperature of the stack during operation, the pressure at various points within the stack, the stack impedance, the cell voltage and the voltage of individual cells, as well as the operating hours and the frequency and type of operating cycles. The state parameters can be determined, in particular, using sensors, with these values ​​advantageously being measured and recorded over an extended period. Using calculation algorithms and empirical data, a degree of degradation of the stack can be determined from these quantities, with the degree of degradation providing information about the type of R. 414398

[0023] - 4 - and the extent of degradation makes predictions about the remaining lifespan

[0024] The degree of degradation allows the optimal operating mode for a given stack to be determined based on its current state. This means determining the voltage and pressure at which the stack can be optimally operated to ensure the highest possible yield of the chemical substance to be produced and / or the longest possible service life. If several stacks are present in the electrochemical plant and are supplied with water and / or electricity in parallel or in series, the plant can no longer be operated optimally if the degradation of all stacks is uneven, as at least some of the stacks cannot be supplied with the optimal voltage, pressure, or amount of water.Based on the determined degree of degradation, the invention provides a recommendation to replace certain stacks whose degree of degradation differs significantly from that of the other stacks. The newly installed stack(s) should have a degradation range comparable to that of the other stacks, so that all stacks can operate optimally without further control measures. If replacement is not currently necessary, but it can be estimated when this will be the case, the recommendation also includes a time at which this replacement should be carried out.

[0025] The condition parameters of the stacks can be determined—where possible—by sensors installed in or on the stack, such as temperatures or pressures inside and outside the stack. These measurements are advantageously recorded and stored throughout the stack's entire lifecycle and then serve to precisely determine the operating state and thus the degree of degradation of the stack, as well as to create a forecast for its future development. Some condition parameters can also be determined through a test cycle. For example, the stack voltage is varied and the change in other stack parameters is measured. Or the pressure inside the stack can be changed and the corresponding response of the stack measured to obtain additional information about the stack's condition. Is the current degree of degradation and R. 414398

[0026] - 5 - if the course of which is known from the recorded measurements, a prediction about the future course can be made with good accuracy and thus a time can be determined at which the replacement of one or more stacks should be carried out.

[0027] The state parameters, that is, the physical values ​​that characterize the stack, can be stored and evaluated directly at the stack or the electrochemical plant in a control unit. These measurements can also be sent to a cloud, where the data is stored, evaluated, and the corresponding degradation level of each stack is determined. Advantageously, the degradation level encompasses the type and extent of the degradation. While the degradation level can be a single number, it usually includes a multitude of values ​​that characterize the degradation level of the respective stack and provide information about the type and extent of the degradation. Advantageously, the degradation level also includes the expected remaining lifetime of the stack.

[0028] The evaluation of state parameters can also be advantageously performed using artificial intelligence. For this purpose, such a system is trained with state parameters from known stacks with known degradation, in order to make a statement about the degree of degradation of the individual stacks based on the measured values ​​and without precise knowledge of the physical relationships.

[0029] The degradation level of the stacks advantageously also includes a recommendation regarding a possible future use or alternative operating mode for the stack to be removed. If a stack is subject to degradation, its use in the original electrochemical plant may no longer be economically viable. However, it is possible that such a stack could still be operated economically in another plant, for example, in a plant that can only be operated intermittently due to infrequent availability of electrical energy. This information in the degradation level can then be used for a different purpose. R. 414398

[0030] - 6 -

[0031] In a further method according to the invention for operating an electrochemical plant, the plant comprises several modules, each module comprising several electrochemical stacks that are electrically and / or hydraulically interconnected within the module. For this purpose, state parameters of each stack are recorded, and a degradation level of each stack is determined using these recorded state parameters. Depending on these degradation levels, a recommendation is issued for exchanging the stacks between the modules. If the stacks in the different modules degrade at different rates, the stacks can be reassembled according to their degradation levels within the modules, so that stacks with the most uniform degradation levels possible can be interconnected within the modules.This allows the modules to be operated effectively with individually adapted operating parameters, and the electrochemical plant can continue to operate efficiently without the need to install new stacks. The recommendation preferably also includes a preferred operating mode for the stacks to be arranged in this module.

[0032] Stacks removed from the electrochemical plant due to their degree of degradation can be stored according to their degradation level if they are not currently needed. Stacks from this storage can then be installed and reused when their degradation at a future date meets the requirements for a replacement stack.

[0033] The drawing shows an electrochemical plant with multiple stacks to illustrate the process according to the invention. It shows:

[0034] Fig. 1 schematically represents an electrochemical plant with a multitude of modules and stacks,

[0035] Fig. 2 shows a representation of a single stack as it can be used in such a system and

[0036] Fig. 3 illustrates the time course of stack degradation. R. 414398

[0037] - 7 -

[0038] Description of the exemplary implementations

[0039] Figure 1 shows an electrochemical plant, specifically an electrolyzer, a device used to electrolytically split water into hydrogen and oxygen. This electrochemical plant comprises three modules 10, 20, and 30, each containing three stacks: the first module 10 contains stacks 11, 12, and 13; the second module 20 contains stacks 21, 22, and 23; and the third module 30 contains stacks 31, 32, and 33. The individual modules are supplied with water or—depending on the type of electrolyzer—with an aqueous electrolytic solution via a water line 100. Since water is supplied in every case, the term "water line" will be used for simplicity. Supply lines 101, 102, and 103 branch off from the water line 100, supplying the individual modules 10, 20, and 30 with water. As already mentioned, each module comprises 10, 20, 30; here, three stacks are shown as examples.Each of these stacks 11, 12, 13 comprises a multitude of electrochemical cells, each having two reaction chambers, which are not shown in detail here, as such electrochemical cells are well known from the prior art.

[0040] The two reaction compartments of an electrochemical cell are also called the anode compartment and the cathode compartment, whereby either only the anode compartment or – depending on the type of electrolyzer – also the cathode compartment is filled with water. The two reaction compartments are separated from each other by a semipermeable membrane, which in the case of a PEM electrolyzer (proton exchange membrane) is only open to hydrogen. + -ions are permeable. A direct current voltage can be applied between the two reaction chambers to enable the desired chemical reaction. Due to a catalytic coating in the anode chamber, water molecules are split there, and the resulting H +-Ions diffuse - driven by the applied electrical voltage - through the membrane into the cathode compartment, where the H + -ions recombine to form H₂ gas, which is flushed out of the cathode compartment along with water. The oxygen remaining in the anode compartment is also flushed out with the water as chlorine gas. The water mixed with the respective gases R. 414398

[0041] - 8 - passes via a hydrogen drain line 200 or an oxygen drain line 300 into - not shown here - gas-water separators, where the gases are separated from the water.

[0042] The stacks within modules 10, 20, and 30 are hydraulically connected in parallel, meaning that the first supply line 101 within the module supplies all stacks 11, 12, and 13 with water in parallel. Simultaneously, all stacks 11, 12, and 13 are electrically connected in series, meaning that the current flows through all stacks 11, 12, and 13 sequentially. For the stacks to operate optimally, each must be supplied with the required amount of water and with the correct voltage and current. Optimization can be performed with regard to lifespan and hydrogen production rate.

[0043] During operation, the stacks degrade, and this degradation can be divided into two categories:

[0044] 1) Membrane thinning: The membrane of the individual electrochemical cells consists of polymers that lose material over time, which is slightly soluble in water. This is primarily due to the highly acidic environment within the membrane, caused by the IT ions. This results in a number of changes, such as reduced mechanical stability, which decreases the possible pressure differential between the reaction chambers and lowers the maximum operating pressure. Furthermore, the ion conductivity increases, resulting in slightly better efficiency at low to medium operating pressures compared to stacks without such degradation.

[0045] 2) Catalyst Degeneration: The membrane facing the anode compartment is coated with a catalytic layer that enables or facilitates the splitting of water. This coating deteriorates over time and reduces the catalytic effect. This decreases efficiency and leads to an increase in the required cell voltage between the anode and cathode compartments, which correspondingly increases the ohmic resistance of the membrane. The required minimum operating temperature also increases, thus reducing the start-up dynamics. R. 414398

[0046] - 9 -

[0047] To determine the degree of degradation, which indicates the type and extent of degradation, state parameters of stacks 11, 12, 13, 21, 22, 23, 31, 32, 33 are recorded or measured. These state parameters can include a wide range of physical quantities, such as temperature in or at the stack, pressure within the stack (both in the anode and cathode circuits), the electrical impedance of the stack as a whole, the voltage at the stack and at the individual cells during operation, the operating hours of the respective stack, and the number of start-up cycles (i.e., how often the stack has been brought from a standby state to an operating state).

[0048] These condition parameters, such as operating hours or startup cycles, can be easily recorded using a clock or counter. For pressure and temperature, these values ​​must be measured and recorded continuously during operation using sensors to obtain the most accurate picture of the stack's condition. However, it may also be useful to determine parameters such as impedance through a test cycle in which different voltages are applied and the stack's response is measured. Figure 2 shows a single stack with a supply line 101 for water or an electrolytic aqueous solution, connecting lines 201 and 301 for hydrogen and oxygen, respectively, and electrical lines 401 and 402 to provide an electrical voltage between the electrodes. A temperature sensor 500 and a pressure sensor 501 are shown as examples on stack 11 and within stack 11.Of course, multiple pressure and temperature sensors can also be used to obtain the most accurate possible picture of the stack's condition. The sensors are connected to an evaluation unit that reads sensor values ​​at regular intervals and stores them for later analysis.

[0049] A degradation level is calculated from the operating parameters using algorithms or artificial intelligence. The degradation level indicates the extent and type of degradation of the individual stacks. From this, it can then be determined which operating parameters are suitable for the R. 414398.

[0050] - 10 -

[0051] It must be operated in a stack to work optimally and have the longest possible remaining lifespan.

[0052] By determining the degree of degradation of the stacks in the electrochemical plant, deviations of individual stacks from the degradation of the other stacks can be identified. For the plant to operate effectively as a whole, all stacks must exhibit approximately the same degree of degradation. Based on the determined degradation levels, individual stacks can now be identified for replacement. The new stack should have a degree of degradation that corresponds to that of the other stacks within certain tolerance ranges. This can be a newly manufactured stack, but also a previously used stack if its degradation is within the acceptable range. After replacing the "deviating" stack, the electrochemical plant can be operated again in such a way that the stacks produce the maximum possible quantity of the desired substance (e.g., hydrogen).

[0053] Figure 3 qualitatively illustrates a possible degradation profile of several stacks. The ordinate, denoted by G, represents the health status of the stacks (i.e., the larger G, the lower the degradation), while the abscissa represents the operating time t of the stacks. The degradation profile is illustrated here for three stacks, a, b, and c, each with its own curve. At time t = 0, all stacks exhibit a health normalized to 1. If the degradation of the stacks is determined at a later time h, a high degree of similarity can be observed between stacks a and b in this example, while stack c shows greater degradation. If this difference is already significant at time h, a recommendation is made to replace stack c with another stack exhibiting similar degradation to stacks a and b.

[0054] If the difference between the stacks at time h is still insignificant, all stacks can continue to operate in one module for the time being. However, based on the degradation profile, which is predicted from the current degradation and the recorded measurements, a time t2 can be determined at which the degradation of stack c will deviate so significantly from that of stacks a and b that it should be replaced with another stack exhibiting similar degradation to stacks a and b. This R. 414398

[0055] - 11 -

[0056] The timing is included in the recommendation so that arrangements for the replacement can be made early, e.g., a suitable time window can be set when the electrolyzer has to be switched off for maintenance work anyway.

[0057] The replaced stack c can potentially be used in another module with other stacks of the same degradation level. It may also be used for a different purpose where the current degradation of stack c is acceptable. However, if the stack eventually reaches a degradation level Geoi that marks the end of its lifespan, continued operation is no longer economically viable, and the stack must be decommissioned—if only for safety reasons. The representation shown here is simplified, as the actual degradation level can include further parameters, particularly the type of degradation.

[0058] If the electrochemical plant comprises several modules, each with a multitude of stacks, the stacks can be advantageously exchanged between the modules. Depending on the determined degree of degradation, individual stacks can be swapped between modules so that their degradation levels are uniform within a specific tolerance range. Stacks whose current degradation level is too low for practical use in a module can also be stored and later reinstalled in a module when the degradation level of the remaining stacks has progressed.

[0059] Depending on the degree of degradation, depleted stacks can also be advantageously used for other purposes. If the electrochemical plant is, for example, an electrolyzer used to produce hydrogen by electrolytically splitting water, a stack may no longer be suitable for use in this plant due to its degradation, but may still be suitable for another application, such as offshore wind power generation. With the method according to the invention, such an application can also be identified in this case, and the stack in question can then be used for that purpose.

Claims

R. 414398 - 12 - Claims 1. Method for operating an electrochemical plant comprising several electrochemical stacks (11; 12; 13; 21; 22; 23; 31; 32; 33) which are electrically and / or hydraulically interconnected, characterized by Capture at least one state parameter of each stack (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33), Determining a degradation level of each stack (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) using the acquired state parameters, issuing a recommendation to replace at least one stack (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) depending on the degradation level of the stack, wherein the recommendation includes a degradation level range that the new stack (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) to be installed should have, and a time at which the replacement should take place.

2. Method according to claim 1, characterized in that the state parameters of the stacks (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) comprise one or more of the following physical quantities: The stack's operating hours to date, - The impedance of the stack (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33), temperature of the water or electrolytic solution in the stack during operation, electrical voltage of the entire stack or of the individual cells during operation, number of start-up cycles.

3. Method according to claim 2, characterized in that at least some of the state parameters are determined by sensors (500) installed in or on the stack (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33). R. 414398 - 13 - 4. Method according to claim 2 or 3, characterized in that at least some of the state parameters are determined by a test cycle.

5. Method according to one of claims 3 or 4, characterized in that the state parameters comprise the course of the underlying physical quantities over the entire or at least over part of the lifetime of the stacks (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33).

6. Method according to any one of claims 1 to 5, characterized in that the degree of degradation includes the type of degradation and the extent of the degradation.

7. Method according to claim 6, characterized in that, in addition to the existing degree of degradation, the expected course of the degree of degradation of the stacks (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) is output.

8. Method according to one of claims 1 to 7, characterized in that the degree of degradation is determined from the state parameters using artificial intelligence.

9. Method according to one of claims 1 to 8, characterized in that the recommendation includes a possible future use and / or operating mode for the stack (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) to be expanded.

10. Method according to one of claims 1 to 9, characterized in that the recorded state parameters are transferred to a cloud and evaluated by a central computer connected to the cloud.

11. Method for operating an electrochemical plant with several modules (10; 20; 30), wherein each module (10; 20; 30) comprises several electrochemical stacks (11; 12; 13; 21; 22; 23; 31; 32; 33) which are electrically and / or hydraulically interconnected, characterized by R. 414398 - 14 - Capture at least one state parameter of each stack (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33), Determining the degradation level of each stack using the captured state parameters, Issuing a recommendation to exchange the stacks (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) between the modules depending on the degradation level of the stacks (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) and a time at which this exchange should take place.

12. Method according to claim 11, characterized in that the recommendation comprises arranging stacks (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) with similar degrees of degradation in each module (10; 20; 30).

13. Method according to claim 12, characterized in that the recommendation includes a preferred operating mode with which the stacks (11 ; 12; 13; 21 ; 22; 23; 31 ; 32; 33) to be arranged in this module (10; 20; 30) should be operated.

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