Method for operating a stack for gas deposition, and control device

Abstract

The invention relates to a method for operating a stack for gas deposition, in particular for carbon dioxide deposition, which stack comprises a plurality of electrochemical cells to which an electrical voltage is applied during operation. According to the invention, when a voltage is applied, the charging current of at least one individual electrochemical cell and / or cell group is measured, a state of charge and / or capacity of the electrochemical cell and / or cell group is determined therefrom, and the cell and / or cell group is temporarily switched off depending on the state of charge and / or capacity. The invention additionally relates to a control device which is designed to carry out a method or individual steps of a method.

Description

[0001] R. 414340

[0002] - 1 -

[0003] Description

[0004] Method for operating a gas separation stack and control unit

[0005] The present invention relates to a method for operating a stack for gas separation, in particular for carbon dioxide separation. Furthermore, the invention relates to a control unit suitable for carrying out the method or operable according to the method.

[0006] The preferred application area of ​​the invention is electrochemical systems or plants for gas separation, in particular for carbon dioxide separation.

[0007] State of the art

[0008] Electrochemical cells used for carbon dioxide capture typically consist of two coated electrodes that are electrically connected and separated by a membrane. This membrane is permeable to ions, which ensure charge balance within the electrochemical cell. At the cathode-side electrode, carbon dioxide from a gas stream or ambient air is captured through chemical processes. The anode-side electrode, on the other hand, acts as an electron donor, providing the electrons necessary for the capture reaction.

[0009] The coating of the cathode-side electrode usually consists of a polymer that can selectively bind gases, such as carbon dioxide, from a gas stream through temperature, pressure, or electrical control. Typical coatings for these electrodes are polymers from the quinone group. The anode-side electrodes, on the other hand, are coated with materials that can release electrons. A common example is R. 414340.

[0010] - 2 - Ferrocenes represent the material group used for coating these electrons. The gas deposition is reversible, meaning that a change in temperature or pressure back to the initial state, or the removal of the voltage, leads to a controlled release of the bound gases, such as carbon dioxide.

[0011] In practical applications, several of these cells are typically stacked and electrically coupled. To avoid the electrical power losses that occur in parallel circuits, these stacks are connected in series, so that the required voltage increases proportionally to the number of cells. However, scaling the voltage with the number of cells, i.e., applying n times the voltage to n cells, presents several problems, since each cell has a specific voltage for optimal operation due to local inequalities between the cells.

[0012] Applying a suboptimal voltage to electrochemical cells can lead to significantly reduced efficiency and / or lifespan, for example due to overheating. Inconsistencies between individual cells in a stack can arise from, for example, differences in manufacturing tolerances, gas concentrations within the cells, varying degrees of aging, or other influencing factors, and are technically unavoidable.

[0013] The present invention is concerned with the objective of increasing the efficiency and lifetime of the cells in the operation of a stack of electrochemical cells.

[0014] 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 process steps is specified.

[0015] Disclosure of the invention

[0016] A method is proposed for operating a stack for gas separation, in particular for carbon dioxide separation, which includes several R. 414340

[0017] - 3 - comprises electrochemical cells to which an electrical voltage is applied during operation. According to the invention, when a voltage is applied, the charging current of at least one individual electrochemical cell and / or cell group is measured, the charge and / or capacity state of the electrochemical cell and / or cell group is determined from this, and depending on the charge and / or capacity state, the cell and / or cell group is temporarily switched off.

[0018] Differences in charge and / or capacity states can arise due to imbalances between cells and / or cell groups. These can be compensated for by switching individual electrochemical cells and / or cell groups on and / or off. In particular, temporarily switching off cells exhibiting extreme charge and / or capacity states can equalize these states. This improves the stack's efficiency and increases the lifespan of the cells and / or cell groups. Measuring the charging current is necessary to determine the charge and / or capacity state of each individual cell or cell group.

[0019] Preferably, with a voltage applied, the charging current of at least one electrochemical cell and / or cell group is measured. From this, the respective state of charge and / or capacity of the electrochemical cell and / or cell group is determined, and a ranking of the electrochemical cells and / or cell groups is created according to their respective state of charge and / or capacity. Creating this ranking identifies the differences between the electrochemical cells and / or cell groups. Cells and / or cell groups whose state of charge and / or capacity deviates significantly from an average occupy an extreme position within the ranking and can thus be clearly identified.

[0020] Furthermore, preferably at least one individual electrochemical cell and / or cell group is temporarily switched off depending on its position in the ranking. Cells and / or cell groups identified based on the ranking with significant deviations can thus be selectively switched off temporarily to equalize the charge and / or capacity states. R. 414340

[0021] - 4 -

[0022] Preferably, at least one temporarily deactivated electrochemical cell and / or cell group is reactivated upon reaching a predetermined position in the ranking. While one cell and / or cell group is temporarily deactivated, the charge and / or capacity states of the remaining cells and / or cell groups change due to the application of an electrical voltage. This alters the positions of the cells and / or cell groups within the ranking and the differences in their positions and capacities between the cells and / or cell groups during operation. By reactivating temporarily deactivated cells and / or cell groups, the charge and capacity states equalize.

[0023] In a further development of the invention, it is proposed that a constant minimum voltage be applied to at least one temporarily deactivated individual electrochemical cell and / or cell group. If an electrochemical cell is deactivated during operation, the reaction reverses and the already bound gas is released again. This can be prevented by applying a minimum voltage, so that the charge level of temporarily deactivated cells is maintained.

[0024] Advantageously, the electrochemical cells and / or cell groups are switched on in a staggered manner during the commissioning of the stack. This staggered switching has the advantage of reducing the electrical load on the system and achieving greater voltage stability. Preferably, the individual cells and / or cell groups are switched on in one or more stages. Grouping the switching of multiple cells and / or cell groups in stages reduces the complexity of the system and thus leads to lower susceptibility to errors and faster processes, since several cells and / or cell groups can be switched on simultaneously.

[0025] Furthermore, preferably, the charging time required to reach a specific final charge state is determined for each electrochemical cell and / or cell group from previous charging cycles. The charging time is a characteristic property of the individual cell or cell group and thus represents a distinguishing feature compared to other cells and / or R. 414340

[0026] - 5 -

[0027] This represents groups of cells. The final charge state of an electrochemical cell and / or cell group is therefore typically reached at different rates. To minimize this difference, it is proposed as a further measure that the staggered connection of electrochemical cells and / or cell groups is based on their respective charging durations. By taking individual charging durations into account, those electrochemical cells and / or cell groups that reach their final charge state more quickly can be connected later. Conversely, electrochemical cells and / or cell groups that reach their final charge state more slowly can be connected earlier. This staggered connection based on individual charging durations ensures that all electrochemical cells and / or cell groups reach their respective final charge states at essentially the same time, allowing the charging process to be terminated.

[0028] In an advantageous further development of the invention, it is proposed that, to determine the condition, in particular the aging condition, of the electrochemical cell and / or cell group, the charge and / or capacity state is determined over time and / or compared with the charge and / or capacity state of another electrochemical cell and / or cell group. By determining the condition, in particular the aging condition, defective cells can be identified and permanently bypassed. If several electrochemical cells within a stack are defective, a necessary replacement of these cells can be signaled. In this way, unplanned failures, downtime, and efficiency losses can be minimized.

[0029] Furthermore, a control unit is proposed that is configured to execute a method or individual steps of a method according to any of the preceding claims. With the aid of the control unit, the measurement of the charging current and the determination of the charge and / or capacity states can be carried out automatically. Furthermore, the control unit is able to create a ranking from the determined data and update this ranking when the charge and / or capacity states change. The updating of the charge and / or capacity states is described in R. 414340.

[0030] - 6 - particularly important for switching individual cells and / or groups of cells on and off.

[0031] Further measures improving the invention are described in more detail below, together with a description of preferred embodiments of the invention, with reference to the figures. These show:

[0032] Fig. 1 shows a flowchart of a method according to the invention in a first preferred embodiment, in which at least one electrochemical cell and / or cell group is temporarily switched off during operation, and

[0033] Fig. 2 shows a flowchart of a method according to the invention in a further preferred embodiment, in which the switching on of the electrochemical cells and / or cell groups takes place in a staggered manner during commissioning.

[0034] Detailed description of the drawings

[0035] As already mentioned, Figure 1 shows a flowchart of a process according to the invention in a first preferred embodiment, in which at least one electrochemical cell and / or cell group is temporarily switched off during operation. The cells and / or cell groups form a stack for the separation of carbon dioxide from a gas or gas mixture.

[0036] In a first step 10, the charging current of at least one cell and / or cell group is measured while a voltage is applied to the electrochemical cells and / or cell groups. In a further step 11, the state of charge and / or capacity of the at least one electrochemical cell and / or cell group is determined from the charging current. Steps 10 and 11 are preferably performed for several, ideally for all, cells and / or cell groups. In a step 12, a ranking of the cells and / or cell groups is created from the states of charge and / or capacity. Based on the ranking, those cells and / or cell groups that occupy an extreme position in the ranking can be identified because their charge- R. 414340

[0037] - 7 - and / or capacity states deviate most significantly from an average charge and / or capacity state. In step 13, at least one cell and / or cell group occupying an extreme position in the ranking is temporarily switched off. This equalizes the charge and / or capacity states of the cells and / or cell groups. In step 14, a minimum voltage is applied to the at least one temporarily switched-off cell and / or cell group. This counteracts a reversal of the electrochemical reaction and thus a release of already bound carbon dioxide. During the temporary switch-off of the at least one electrochemical cell and / or cell group, its position in the ranking is continuously updated by repeating steps 10-12.If the previously occupied marginal position in the ranking is left, in step 15 at least one temporarily deactivated cell and / or cell group is reactivated.

[0038] As already mentioned, Figure 2 shows a flowchart of a method according to a further preferred embodiment of the invention, in which the electrochemical cells and / or cell groups are switched on in a staggered manner during commissioning. In step 20, charging and / or capacity data of the electrochemical cells and / or cell groups are collected during a first charging cycle. In step 21, the respective charging time of the electrochemical cells and / or cell groups required to reach a final charging state is determined from the data collected in step 20. In step 22, based on the determined charging times, the electrochemical cells and / or cell groups are switched on in a staggered manner, so that essentially all cells and / or cell groups reach their final charging state simultaneously.

Claims

R. 414340 - 8 - Claims 1. Method for operating a stack for gas separation, in particular for carbon dioxide separation, comprising several electrochemical cells to which an electrical voltage is applied during operation, characterized in that, when a voltage is applied, the charging current of at least one individual electrochemical cell and / or cell group is measured, a charge and / or capacity state of the electrochemical cell and / or cell group is determined from this, and depending on the charge and / or capacity state, the cell and / or cell group is temporarily switched off.

2. Method according to claim 1, characterized in that, with applied voltage, the charging current of at least one individual electrochemical cell and / or cell group is measured, the respective charge and / or capacity state of the electrochemical cells and / or cell groups is determined from this, and a ranking of the electrochemical cells and / or cell groups is created according to their respective charge and / or capacity state.

3. Method according to claim 2, characterized in that at least one individual electrochemical cell and / or cell group is temporarily switched off depending on its position in the ranking.

4. Method according to claim 2 or 3, characterized in that at least one temporarily deactivated individual electrochemical cell and / or cell group is reactivated upon reaching a predetermined position in the ranking.

5. Method according to any of the preceding claims, R. 414340 - 9 - characterized in that a constant minimum voltage is applied to at least one temporarily switched-off electrochemical cell and / or cell group.

6. Method according to one of the preceding claims, characterized in that, when the stack is put into operation, the electrochemical cells and / or cell groups are switched on in a staggered manner, preferably in one or more stages.

7. Method according to one of the preceding claims, characterized in that the charging time required to reach a specific final charging state is determined from previous charging cycles for each electrochemical cell and / or cell group, wherein preferably the time-staggered switching on of electrochemical cells and / or cell groups takes place depending on the respective charging time.

8. Method according to one of the preceding claims, characterized in that, in order to determine a state, in particular an aging state of the electrochemical cell and / or cell group, the charge and / or capacity state is determined over time and / or compared with the charge and / or capacity state of another electrochemical cell and / or cell group.

9. Control unit configured to execute a method or individual steps of a method according to any of the preceding claims.

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