Method of operating an electrolysis system, control unit

Abstract

The invention relates to a method of operating an electrolysis system having a plurality of stacks, each of which comprises a plurality of individual cells in a stacked arrangement, where each individual cell has an anode and a cathode that are separated by a membrane. According to the invention, by defining a lower power threshold (Pmid,low) and an upper power threshold (Pmid,high), an average power range in which the ageing rate (AR) of the membranes reaches a maximum is defined, and, in order to reduce membrane ageing, the available electrical power (P) is divided between one or more stacks so as to avoid operation of any individual stack in the average power range. The invention further relates to a control unit for executing steps of the method according to the invention.

Description

[0001] Description

[0002] Method for operating an electrolysis system, control unit

[0003] The present invention relates to a method for operating an electrolysis system with the features of the preamble of claim 1. Furthermore, the invention relates to a control unit for carrying out steps of the method according to the invention.

[0004] A preferred application area of ​​the invention is electrolysis systems for the production of hydrogen.

[0005] State of the art

[0006] The market for equipment and technologies used to produce "green" hydrogen through electrolysis is growing rapidly and steadily. Driven by the goal of decarbonization, this growth will continue to accelerate and increase in importance in the coming years. Currently, plans are underway for large-scale, industrial-scale hydrogen production through electrolysis. The aim is to develop plants capable of operating at capacities exceeding 1 GW.

[0007] The electrochemical reaction for producing hydrogen by electrolysis takes place in an electrolysis cell. This cell has an anode and a cathode, separated by a membrane. An electrolyte, such as water, is supplied to the anode, where it is split into the product gases hydrogen and oxygen. The hydrogen is produced at the cathode, and the oxygen at the anode. To increase gas production, multiple electrolysis cells are stacked on top of each other to form a stack.

[0008] In addition to the stack, an electrolysis system requires other components, in particular power supply equipment, an electrolyte circuit to supply the stack with the electrolyte, equipment for processing the product gases, in particular gas-liquid separators, control and / or regulation equipment, and safety technology.

[0009] Typical system designs comprise several stacks that are combined into a unit, also called a cluster. Each unit usually has its own control unit, which allows the load or electrical power to be distributed across the multiple stacks.

[0010] The present invention is concerned with the objective of reducing the membrane aging of the electrolysis cells during the operation of an electrolysis system comprising several stacks, in order to thereby increase the lifetime of the electrolysis system.

[0011] 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 steps of the method is specified.

[0012] Disclosure of the invention

[0013] A method is proposed for operating an electrolysis system with multiple stacks, each stack comprising a plurality of individual cells in a stacked arrangement, wherein each individual cell has an anode and a cathode separated by a membrane. According to the invention, by defining a lower power threshold and an upper power threshold, a medium power range is defined in which the aging rate of the membranes reaches a maximum. To reduce membrane aging, the available electrical power is distributed among one or more stacks in such a way that operation of a single stack in the medium power range is avoided. The invention is based on the understanding that the aging rate, in particular the rate of chemical aging, of the membranes is a function of the power.This relationship between aging rate and performance is used here to achieve a membrane-aging-optimized power distribution across the multiple stacks of the electrolysis system. A prerequisite for carrying out the procedure is therefore that the electrolysis system comprises multiple stacks.

[0014] Depending on the available electrical power, it should be distributed so that a few stacks are operated above the upper power threshold, rather than distributing the power evenly. If insufficient power is available to operate at least one stack above the upper power threshold, operating at least one stack below the lower power threshold may be an option.

[0015] The proposed method enables a significant reduction in the aging of the membranes of the individual cells in all stacks, with a reduction of up to 30% expected. This results in a correspondingly significant increase in the stack lifetime and thus the lifetime of the electrolysis system. A key metric for assessing system efficiency is the levelized cost of hydrogen (LCOH) over the lifetime of the electrolysis system. An increased lifetime has a positive impact on the LCOH metric.

[0016] The aging rate as a function of performance is assumed to be known. If it is not known, it is preferably determined for all stacks, for example by laboratory measurements or by derivation from literature values.

[0017] Knowing the aging rate, the average performance range can then be defined by setting the lower and upper performance thresholds. This can be done as described below. Preferably, the upper performance threshold is set first. Furthermore, preferably, the upper performance threshold is set to a value for which the following holds for the aging rate (AR): R(Pmid, high) R (Pmid, high / -stacks) where n stacks indicates the number of stacks in the electrolysis system.

[0018] The lower power threshold can then be determined, preferably according to the following equation: in the n stacks This indicates the number of stacks in the electrolysis system. The two threshold values ​​are thus in a defined relationship to each other via the number of stacks.

[0019] Advantageously, the aging of the stacks is monitored during operation of the electrolysis system, and the aging rate is dynamically adjusted. This monitoring can be performed using a "state-of-health monitoring" system to obtain information about the current aging status of each individual stack.

[0020] Furthermore, it is proposed that the available electrical power be distributed to the stack(s) whose aging is least advanced. In this way, an approximately uniform aging of all stacks can be achieved. In particular, variations in aging rates, resulting, for example, from manufacturing tolerances, can be compensated for.

[0021] Alternatively or additionally, it is proposed that the available electrical power be distributed across alternating stacks. This measure also contributes to ensuring that all stacks age as evenly as possible.

[0022] In a further development of the invention, it is proposed that the available electrical power be temporarily stored in a battery when it is insufficient to operate a single stack above the upper power threshold. The battery can absorb power and thus load peaks, both upwards and downwards, thereby further reducing membrane aging. Furthermore, other situations are conceivable in which temporary storage is advantageous. For example, the discharge from the battery can be designed to optimize membrane aging. The battery can be located anywhere between the power source and the electrolysis system. This means that the battery is not necessarily part of the electrolysis system.

[0023] The proposed operating strategy can lead to frequent switching on and off of the stacks if the available electrical power fluctuates around the lower or upper power threshold. Various measures can be implemented to avoid such "toggling".

[0024] A first measure stipulates that a holding period is observed before a stack is switched on or off. Switching a stack on and off can be carried out using a predictive model that forecasts the available electrical power. Based on this forecast, a suitable power distribution can then be selected. The predictive model could, for example, be one that takes into account information from a primary energy supplier, in particular information about cloud movement, sun position, wind direction, wind speed, and / or other weather data.

[0025] Other possible measures include using a battery as an intermediate storage device and / or temporarily limiting the available electrical power.

[0026] Furthermore, a control unit for an electrolysis system is proposed. The control unit is configured to execute steps of a method according to the invention. In particular, the control unit can be used for power distribution according to the method of the invention. The invention and its advantages are described in more detail below with reference to the accompanying drawings and figures. These show:

[0027] Fig. 1 a) and b) Diagrams illustrating different trends in aging rates,

[0028] Fig. 2 shows a diagram illustrating an aging rate (AR) as a function of electrical power (P) and

[0029] Fig. 3 is a diagram illustrating the expected reduction in membrane aging when using the method according to the invention.

[0030] Detailed description of the drawings

[0031] There is a relationship between chemical membrane aging, i.e., the thinning of a membrane, and the current density of the electric current applied to an electrolysis cell. This relationship can be seen by way of example in Figures 1a) and 1b), which show the aging rate profiles of different membranes (A, B, C, D, E).

[0032] In Figures 1a) and 1b), FRRA is the rate at which a portion of the membrane is washed out. In this case, it is fluorine contained in the membrane's ionomer. FRRA can therefore be equated with the aging rate AR. The x-axis represents the current density. This enters the power equation quadratically, since power is the product of current and voltage, and voltage is linearly dependent on current. The investigated membranes all exhibit similar behavior.

[0033] The aging rate AR can therefore be defined as a function of the electrical power P.

[0034] Based on this finding, the inventive method proposes a membrane-aging-optimized operating strategy for a multi-stack electrolysis system. Instead of a uniform power distribution across all stacks, this strategy involves operating individual stacks outside a medium power range, as the aging rate reaches a maximum in the medium power range. By avoiding stack operation in the medium power range, membrane aging can thus be reduced. As illustrated by way of example in Figure 2, the medium power range can be defined by a lower power threshold Pmid.iow and an upper power threshold Pmid.high. The two power thresholds are set such that the aging rate AR is the same as a function of the power P, and the following condition is also met:

[0035] As illustrated in the figure, the proposed operating strategy can reduce the aging rate AR by approximately 30%.

Claims

Claims 1. A method for operating an electrolysis system with multiple stacks, each comprising a plurality of individual cells in a stacked arrangement, wherein each individual cell has an anode and a cathode separated by a membrane, characterized in that by setting a lower power threshold (Pmid.iow) and an upper power threshold (P m id,hi g h) a medium power range is defined in which the aging rate (AR) of the membranes reaches a maximum, and in order to reduce membrane aging, the available electrical power (P) is distributed among one or more stacks in such a way as to avoid operating a single stack in the medium power range.

2. Method according to claim 1, characterized in that the aging rate (AR) is determined as a function of the power (P) for all stacks, for example by measuring in the laboratory or by deriving from literature values.

3. Method according to claim 1 or 2, characterized in that the upper power threshold (P m id,hi g h) is set to a value such that the aging rate (AR) is: R(Pmid, high) R (Pmid,high / -stacks) where n stacks indicates the number of stacks in the electrolysis system.

4. Method according to one of the preceding claims, characterized in that the lower power threshold (Pmid.iow) is determined according to the following equation PMID, high ' mid, low ~~~ ''■stacks in the n stacks indicates the number of stacks in the electrolysis system.

5. Method according to one of the preceding claims, characterized in that the aging of the stacks is monitored during operation of the electrolysis system and the aging rate (AR) is dynamically adjusted.

6. Method according to one of the preceding claims, characterized in that the available electrical power (P) is distributed to the stack(s) whose aging is least advanced.

7. Method according to one of the preceding claims, characterized in that the available electrical power (P) is distributed among alternating stacks.

8. Method according to one of the preceding claims, characterized in that the available electrical power (P) is temporarily stored in a battery when it is required for the operation of a single stack above the upper power threshold (P). m id,hi g h) is too small.

9. Method according to one of the preceding claims, characterized in that a holding time is observed before a stack is switched on or off.

10. Control unit for an electrolysis system, wherein the control unit is configured to perform steps of a method according to one of the preceding claims.

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