Method for operating an electrochemical cell and control unit

Abstract

A method for operating an electrochemical cell for gas separation is proposed. In this method, during a gas separation process, a gas mixture containing the gas to be separated is supplied to the electrochemical cell, and an electrical voltage is applied to the electrochemical cell. During a gas release process, the separated gas is released again by changing the electrical voltage. According to the invention, at the beginning of a gas separation process, the amount of electrical charge required for gas separation is calculated, and to optimize the gas separation process, in particular to reduce energy consumption during the gas separation process, the applied electrical voltage and / or the electrical current density are dynamically adjusted using several calibration curves.The calibration curves describe the current density resulting from the applied electrical voltage as a function of at least one other operating parameter, for example, the current charge state of the electrochemical cell and / or the current composition of the gas mixture. Furthermore, the invention relates to a control unit that is configured to carry out a method or individual steps of a method.

Description

[0001] The present invention relates to a method for operating an electrochemical cell for gas separation, in particular for carbon dioxide separation. Furthermore, the invention relates to a control unit suitable for carrying out the method or individual steps of the method.

[0002] The preferred application area of ​​the invention is electrochemical systems or plants for carbon dioxide separation. State of the art

[0003] Electrochemical cells used for gas separation, particularly carbon dioxide separation, typically have two electrodes that are electrically connected and separated by a separator. Both the separator and the electrodes are usually immersed in or surrounded by an electrolyte, which ensures charge balance within the electrochemical cell. At the first electrode, located on the cathode side, the gas to be separated, for example, carbon dioxide, is captured from a gas stream through an electrochemical process and bound. Gas separation is generally initiated by a change in electrical voltage. The separation process is reversible, meaning that removing or reversing the voltage causes a controlled release of the previously separated and bound gas.In this process, a second electrode on the anode side acts as an electron donor, providing the electrons necessary for the deposition reaction. The gas stream containing the gas to be deposited typically originates from combustion processes or other production processes that generate gas mixtures as exhaust gas. These gas mixtures often contain carbon dioxide.

[0004] In electrochemical cells, the electrical voltage is coupled to the electrical current density. This means that applying an electrical voltage results in a corresponding current density, and vice versa. The relationship between electrical voltage and current density is typically expressed as a voltage-current density curve. The applied electrical voltage is typically varied to adjust the electrical current density. The applied electrical voltage and the resulting current density (or vice versa) significantly influence the efficiency and duration of gas separation, and thus the energy consumption of the electrochemical cell.

[0005] In practice, a difference between the theoretical voltage and the actual voltage required is often observed during gas separation using electrochemical cells. These so-called overvoltages are due to various energy losses within the electrochemical cells. These energy losses can be caused, for example, by the resistance of the electrolyte or by the activation energy of the electrochemical reaction. They cumulatively increase the electrical voltage required to generate a defined current density. The magnitude of the respective overvoltages is not constant, but depends on the specific cell and the applied electrical voltage or current density. Consequently, there is a non-linear and therefore complex relationship between the electrical voltage and the resulting electrical current density.In addition, the voltage-current density curve depends on further operating parameters, such as the state of charge of the electrochemical cell, the concentration of the gas to be separated in the gas stream, or the cell's state of aging. This makes predicting the correlation between electrical voltage and current density more difficult.

[0006] The present invention is concerned with the objective of optimizing the gas separation process, particularly with regard to energy consumption, the avoidance of overvoltages and / or the increase of efficiency.

[0007] To solve the problem, the method with the features of claim 1 is proposed. Advantageous embodiments of the invention are described in the dependent claims. Furthermore, a control unit for executing the method or individual steps of the method is specified. Disclosure of the invention

[0008] A method for operating an electrochemical cell for gas separation is proposed. In this method, during a gas separation process, a gas mixture containing the gas to be separated is supplied to the electrochemical cell, and an electrical voltage is applied to the electrochemical cell. During a gas release process, the separated gas is released again by changing the electrical voltage. According to the invention, at the beginning of a gas separation process, the amount of electrical charge required for gas separation is calculated, and to optimize the gas separation process, in particular to reduce energy consumption during the process, the applied electrical voltage and / or the electrical current density are dynamically adjusted using several calibration curves.The calibration curves describe the current density resulting from the applied electrical voltage as a function of at least one other operating parameter, for example the current state of charge of the electrochemical cell and / or the current composition of the gas mixture.

[0009] Optimizing the gas separation process aims to optimize at least one operational parameter. This can particularly involve energy consumption, where the goal is to reduce energy consumption, e.g.: • Minimizing energy consumption per output variable; the output variable could be, for example, per kWh for combined heat and power plants or per nautical mile for installation in ships. • Minimizing energy consumption while adhering to fixed boundary conditions such as a capture rate.

[0010] Alternatively or additionally, the objective can also be to minimize the TCO (Total Cost of Operation) and / or to maximize the lifespan of the electrochemical cell. Maximizing the lifespan can be achieved, for example, by: • Setting boundary conditions - fixed or dynamic limitation of voltage or current - Limitation of the load per cycle • Targeted optimization: - Minimizing the number of cycles per kg of CO2 while adhering to the defined boundary conditions, - Maximizing service life when influences on service life are quantitatively documented.

[0011] Particularly with regard to the objective of reducing energy consumption, the proposed dynamic adjustment of the applied electrical voltage or current density, using calibration curves, can increase the electrical efficiency and thereby reduce the energy consumption of the electrochemical cell. Determining calibration curves allows for an analysis of the current density resulting from each applied electrical voltage and, using the amount of charge to be transferred, a calculation of an energetically advantageous applied electrical voltage and / or current density. The same procedure can be used for the other objectives mentioned above.

[0012] In electrochemical cells, changes in operating parameters, such as the current charge state of the electrochemical cell and / or the current composition of the gas mixture, cause a shift in the correlation between applied voltage and current density. This necessitates a continuous adjustment of the voltage and current density to reflect changes in the operating parameters. This is achieved through dynamic voltage and current density adjustment. When operating parameters change, the voltage and current density are adjusted to minimize energy consumption.

[0013] Preferably, the amount of electrical charge required for gas separation is calculated from a given quantity of gas to be separated. The quantity of gas to be separated is an important target parameter of the electrochemical cell, which is why the calculated amount of charge is a particularly important boundary condition for the present method for reducing the energy consumption of the electrochemical cell. Furthermore, the calculated amount of charge allows for a prediction of the required electrical energy, enabling its early provision and thus improving the operation of the electrochemical cell.

[0014] Furthermore, calibration curves are preferably used, which are determined before commissioning the electrochemical cell at a defined value of at least one operating parameter. The overvoltages and the correlation between applied electrical voltage and current density are each dependent on the current operating parameters. For this reason, the calibration curves are also determined as a function of at least one value of the operating parameter. This allows for dynamic adjustment of the applied electrical voltage and / or current density during the gas separation process for each defined operating state. In this way, energy consumption can be reduced even with changing operating parameters, thereby increasing the efficiency of the electrochemical cell.

[0015] Advantageously, for each calibration curve, a pair of values ​​consisting of applied electrical voltage and / or electrical current density is determined that, compared to all other pairs of values ​​on the respective calibration curve, reduces energy consumption per required charge quantity most significantly. The calibration curve allows knowledge of the electrical current density resulting from the applied electrical voltage and thus of all possible pairs of values ​​applied to the electrochemical cell. This enables the identification of the pair of values ​​with the lowest energy consumption per required charge quantity. By proactively determining the pair of values ​​with the lowest energy consumption per required charge quantity for all calibration curves, a faster response of the process to changing operating parameters can be achieved. In particular, proactively determining the most energy-efficient pair of values ​​saves computation time.

[0016] In a further development of the invention, it is proposed that at least one calibration curve be selected from the multiple calibration curves for dynamically adjusting the applied electrical voltage and / or the electrical current density. This selected calibration curve was determined at a value of the at least one operating parameter that most closely approximates the current value of the at least one operating parameter. The multiple calibration curves were determined based on defined values ​​of the at least one operating parameter and, as such, are specific to a particular operating state. A deviation from this operating state leads to a change in the correlation between electrical voltage and current density.For this reason, the calibration curve determined for an operating parameter value that most closely approximates the current value of at least one operating parameter most accurately describes the actual correlation between electrical voltage and / or current density. In this way, a very precise dynamic adjustment of the applied electrical voltage and / or current density can be achieved to minimize energy losses.

[0017] When selecting from several calibration curves, the one used to adjust the applied electrical voltage and / or current density is preferred, as its pair of values ​​most significantly reduces energy consumption per unit of charge required. Multiple calibration curves are selected when the defined values ​​of the corresponding operating parameters of the calibration curves are all essentially equally close to the current operating parameters of the electrochemical cell and thus equally suitable for dynamic adjustment. From these, the calibration curve whose pair of values ​​most significantly reduces energy consumption per unit of charge required is then selected.

[0018] The energy consumption of an electrochemical cell can be reduced not only during gas separation, but also during the reverse process, i.e., during gas release.

[0019] In a further development of the invention, it is therefore proposed that, during a gas release process, the applied electrical voltage and / or the electrical current density are dynamically adjusted using several calibration curves to reduce energy consumption per required charge. The calibration curves describe the electrical current density resulting from the applied electrical voltage as a function of the gas release rate and the current charge state of the electrochemical cell. In this way, the aforementioned advantages can also be applied to gas release using several calibration curves. By dynamically adjusting the applied electrical voltage and / or the electrical current density, the influence of at least one changing operating parameter can be compensated for, thus increasing efficiency and decreasing energy consumption.

[0020] Advantageously, at least one of the several calibration curves is recalculated, interrupting the operation of the electrochemical cell to determine this curve. The calibration curves depend not only on the operating parameters but also on the condition of the electrochemical cell. In the case of wear or aging processes, the correlation between electrical voltage and current density changes. For this reason, recalculating the calibration curves leads to better dynamic adaptation and thus higher efficiency of the electrochemical cell. Interrupting the operation of the electrochemical cell during the calibration process is necessary to record the calibration curve at a defined operating parameter and to avoid fluctuations in this parameter.The calibration curves determined in this way exhibit higher accuracy, thereby improving the dynamic adjustment of the applied electrical voltage and / or current density.

[0021] In a further development of the invention, the condition, in particular the aging state, of the electrochemical cell is determined based on the calibration curves and / or the change in the calibration curves over time. By determining the condition, especially the aging state, an impending defect can be identified and a necessary cell replacement detected. In this way, unplanned failures, downtime, and efficiency losses can be minimized.

[0022] Furthermore, a control unit is proposed. This unit is designed to execute the inventive method or individual steps thereof. In particular, the control unit can be used to control and monitor the dynamic adjustment of the applied electrical voltage and / or the electrical current density.

[0023] The invention and its advantages are explained in more detail below with reference to the accompanying figure. This figure shows an exemplary flowchart of a method according to the invention for operating an electrochemical cell for gas separation. Detailed description of the drawing

[0024] In the method illustrated by the figure, the applied electrical voltage and / or current density are dynamically adjusted using several calibration curves to reduce energy consumption per required amount of charge.

[0025] In the first process step 10, the boundary conditions of the process are defined. These include, for example, the amount of gas to be separated and the maximum voltage and current density that are technically feasible. Furthermore, values ​​are defined for at least one operating parameter, at which the calibration curves are recorded.

[0026] In a subsequent step 11, these calibration curves are determined as a function of the operating parameter values. This determination is performed for the first time before the electrochemical cell is commissioned – not shown here – and in all subsequent determinations in step 11. For each calibration curve, the value of at least one associated operating parameter is set, and the resulting current density from each applied voltage is determined. The voltage and current density are varied only within the technically feasible boundary conditions, up to a maximum voltage and current density.In step 11, when re-determining one or more of the calibration curves, the operation of the electrochemical cell is interrupted, the values ​​of at least one operating parameter are set, and the electrical voltage and current density are recorded again. In a subsequent step 12, the amount of charge required for gas separation is calculated from the amount of gas to be separated. This calculation can also be performed using a planned separation rate and the duration of the gas separation.

[0027] In a further step 13, for each determined calibration curve, the pair of values ​​for electrical voltage and electrical current density is calculated which, compared to all other pairs of values ​​for the respective calibration curve, exhibits the lowest energy consumption per unit of transferred charge. This yields an energetically advantageous operating point for each calibration curve. In a subsequent step 14, the current value of at least one operating parameter of the electrochemical cell is measured and compared with the defined values ​​of the at least one operating parameter for which the calibration curves were determined. The at least one calibration curve whose value of the at least one operating parameter is closest to the currently measured value of the operating parameter is then selected, as this calibration curve most accurately describes the actual correlation between electrical voltage and current density.If only one calibration curve is selected, step 16 is performed next. However, multiple calibration curves can also be selected, for example, several calibration curves that differ only in their charging rate. In this case, step 15 compares the calculated energy consumption of the calibration curves and selects the one with the lowest energy consumption per transferred charge. Step 15 is then also followed by step 16.

[0028] In step 16, it is also checked whether the current value of at least one operating parameter exceeds a defined deviation from the value of the at least one operating parameter for which the calibration curve was recorded. If this is the case, step 14 is repeated, and the calibration curves are selected again based on the proximity of the value of their respective at least one operating parameter to the current value of the operating parameter. This selection of the most energy-efficient calibration curve with the most energy-efficient value pair, as well as the dynamic adjustment or iteration based on the calibration curves, ensures that the efficiency of the electrochemical cell is increased and energy consumption is minimized.

[0029] The process steps described above with reference to the figure during a gas separation process are also applicable analogously to a gas release process. The at least one operating parameter can be, in particular, the release rate or the loading state in discharge mode. For this purpose, the process steps from step 10 onwards for the gas release process are simply repeated after completion of a gas separation process.

[0030] Depending on key performance indicators, such as operating time or achieved efficiency, recalculating the calibration curves can be advantageous. In this case, the operation of the electrochemical cell is interrupted in step 16, and step 11 is repeated to calculate the calibration curves. This may be necessary, for example, because electrochemical cells are subject to natural wear and aging, which also affect the calibration curves. After this recalculation of the calibration curves, the aging state of the electrochemical cell is calculated in step 17, which is inserted between steps 11 and 12. This can be determined by comparing and, in particular, observing changes in the calibration curves and serves to identify an impending defect and detect a necessary replacement of the electrochemical cell in order to avoid unplanned failures, downtime, and efficiency losses.After calculating the state of aging, the procedure continues with step 12 as described.

Claims

[1] Method for operating an electrochemical cell for gas separation, wherein during a gas separation process the electrochemical cell is supplied with a gas mixture containing the gas to be separated and an electrical voltage is applied to the electrochemical cell and wherein during a gas release process the separated gas is released again by changing the electrical voltage, characterized by, that at the beginning of a gas separation process the amount of electrical charge required for gas separation is calculated and, in order to optimize the gas separation process, in particular to reduce energy consumption during the gas separation process, the applied electrical voltage and / or the electrical current density is / are dynamically adjusted using several calibration curves, wherein the calibration curves determine the current density resulting from the applied electrical voltage as a function of at least one other operating parameter, for example - the current state of charge of the electrochemical cell and / or - describe the current composition of the gas mixture. [2] Method according to claim 1, characterized by , that the amount of electrical charge required for gas separation is calculated from a given amount of gas to be separated. [3] Method according to claim 1 or 2, characterized by, that calibration curves are used which were determined before commissioning the electrochemical cell at a defined value of at least one operating parameter. [4] Method according to any one of the preceding claims, characterized by , that for each calibration curve a pair of values ​​of applied electrical voltage and / or electrical current density is determined which, compared to all other pairs of values ​​of the respective calibration curve, reduces the energy consumption per required amount of charge the most. [5] Method according to any one of the preceding claims, characterized by , that from the several calibration curves at least one calibration curve is selected for the dynamic adjustment of the applied electrical voltage and / or the electrical current density, which has been determined at a value of the at least one operating parameter that is closest to the current value of the at least one operating parameter. [6] Method according to claim 5, characterized by , that when selecting several calibration curves, the one used to adjust the applied electrical voltage and / or electrical current density is the one whose pair of values ​​reduces the energy consumption per required amount of charge the most. [7] Method according to any of the preceding claims, characterized by , that during a gas release process, in order to reduce energy consumption per required charge quantity, the electrical voltage and / or the electrical current density applied during the gas release process is / are dynamically adjusted using several calibration curves, wherein the at least one calibration curve describes the current density resulting from the applied electrical voltage as a function of the gas release rate and the current charge state of the electrochemical cell. [8] Method according to any one of the preceding claims, characterized by, that at least one of the several calibration curves is recalculated, whereby the operation of the electrochemical cell is interrupted to determine the at least one calibration curve. [9] Method according to any one of the preceding claims, characterized by , that a condition, in particular an aging condition of the electrochemical cell, is determined based on the calibration curves and / or the change of the calibration curves over time. [10] Control unit configured to execute a method or individual steps of a method according to any of the preceding claims.

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