Method of operating an electrolysis system and electrolysis system

Abstract

The invention presented relates to a method (100) of operating an electrolysis system (200, 300). The method (100) presented comprises: - maximizing (101) a fill level of a gas-liquid separator (203, 303) of the electrolysis system (200, 300) before an electrolysis activity of the electrolysis system (200, 300) is stopped, - purging (103) at least one cell stack (201, 301) of the electrolysis system (200, 300) with a first fluid and at least one further fluid other than the first fluid before the electrolysis activity of the electrolysis system (200, 300) is stopped.

Description

[0001] Description

[0002] title

[0003] Method for operating a and

[0004] The presented invention relates to a method for operating an electrolysis system and an electrolysis system according to the appended claims.

[0005] State of the art

[0006] An essential element of electrolysis systems is the electrolysis stack or cell stack, which splits water into its components hydrogen (H2) and oxygen (O2) in an electrochemical process, e.g. using electricity.

[0007] There are various types of cell stacks, such as PEM (proton exchange membrane), SOEC (solid oxide electrolysis cell), alkali and AEM (anion exchange membrane) cell stacks, which differ in particular in the type of ion transport across the membrane (H + , OH , O 2 ).

[0008] The cell stacks are usually integrated into an electrolysis system in which the stacks are supplied with water, for example by a pump, which may also be passed through a heat exchanger and a filter. On both sides of a cell in the cell stack - anode and cathode - the product gases (O2 and H2) are produced when a voltage is applied, sometimes with larger amounts of reactant (water). These product gases are usually fed to a gas-liquid separator, in which the respective gas is separated from the liquid, before the hydrogen, in particular, is further processed in any subsequent processes (in particular drying, purification, compression). Since hydrogen can only be considered "green" - i.e.While a system can be described as carbon-neutral if electricity is exclusively generated from renewable energy sources, usually wind and photovoltaics, and less frequently from hydropower or geothermal energy, the operation of an electrolysis system generally cannot be carried out at a constant operating point, but must be based on electricity availability. This results in the requirement that dynamic operation and intermittent downtimes be provided for during the operation of an electrolyzer.

[0009] The energy efficiency of electrolysis systems depends primarily on their power consumption relative to the amount of hydrogen produced or usable. Maintaining energy efficiency as high as possible is challenging given the varying operating conditions and, in particular, the intermittent downtimes caused by standby or extended shutdown periods.

[0010] For safety reasons, when shutting down an electrolysis system, the hydrogen side in particular is usually purged with an inert gas, usually nitrogen (N2). This prevents hydrogen from diffusing to the hydrogen side and reacting there and / or otherwise forming an ignitable gas mixture.

[0011] When restarting an electrolysis system, the problem arises that the produced hydrogen is mixed with N2 and may not meet the required purity for use. To prevent this, a quantity of newly produced gas is discarded for a specified operating period during startup after a shutdown or standby phase. This reduces the hydrogen yield and plant efficiency.

[0012] Disclosure of the invention

[0013] Within the scope of the invention presented, a method for operating an electrolysis system and an electrolysis system are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the electrolysis system according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0014] The invention presented serves in particular to operate an electrolysis system in an energy-efficient manner.

[0015] Thus, according to a first aspect of the invention presented, a method for operating an electrolysis system is presented.

[0016] The presented method comprises maximizing a fill level of a gas-liquid separator of the electrolysis system, in particular of the Fh-side gas-liquid separator and optionally of the Oj-side gas-liquid separator, before an electrolysis activity of the electrolysis system is discontinued, and flushing at least one cell stack of the electrolysis system with a first fluid and at least one further fluid different from the first fluid, for example a second or third fluid, before the electrolysis activity of the electrolysis system is discontinued.

[0017] In the context of the present invention, maximizing the fill level of a gas-liquid separator means increasing the amount of liquid present in the gas-liquid separator or minimizing the gas phase present in the gas-liquid separator. In particular, maximizing the fill level of a gas-liquid separator involves completely filling the gas-liquid separator or filling the gas-liquid separator to a predetermined target level or minimum level.

[0018] The presented invention is based on the principle of predictive operation, in which, on the one hand, safety aspects are met by purging the cell stack or other parts of the electrolysis system with inert gas such as nitrogen, while, at the same time, the effects of the resulting foreign gas ingress are reduced by level control in the gas-liquid separator and a purging procedure with several different fluids. This allows for a reduction in the amount of waste Fh, which significantly improves or maximizes the Fh yield and the energy efficiency of a corresponding electrolysis system, especially during frequent standby and / or shutdown periods.

[0019] The liquid level in the gas-liquid separator directly influences the gas quantity in the separator. The higher the level, the lower the gas quantity. During normal operation, the liquid level is controlled to a constant level to optimize the residence time of a two-phase mixture and thus the outgassing of the respective product gases, H2 or O2.

[0020] According to the method presented, it can be provided, in particular, that when an electrolysis activity of the electrolysis system is planned or foreseeable, the fill level of the gas-liquid separator is continuously increased, for example, with a lead time, in particular between 30 minutes and 60 minutes, in order to achieve a maximum fill level of liquid in the gas-liquid separator, for example, until the cell stack is shut down or the electrolysis system goes into standby, and accordingly to reduce the gas space remaining in the gas-liquid separator to a minimum. In particular, the maximizing and purging can be carried out during a shutdown or while a shutdown procedure is initiated or carried out, so that a corresponding electrolysis system is conditioned for a switched-off state and, in particular, a restart state.

[0021] The increase in the liquid level in the gas-liquid separator can be achieved, for example, by throttling or completely stopping the discharged amount at the water-side outlet of the gas-liquid separator using an outlet valve. In another embodiment, liquid can also be actively added to increase the level particularly quickly, for example.

[0022] The method may further include determining a trigger condition that leads to the cessation of the electrolysis activity of the electrolysis system. Determining the trigger condition may, for example, be the receipt of a shutdown command, the detection of a voltage in a power supply system that is below a predetermined target value, a forecast of available electrical power and its price, for example, on the stock exchange, and / or a report of an expected weather phenomenon according to a predetermined list of weather phenomena.

[0023] Accordingly, the method presented can be used to prepare an electrolysis system for a process to adjust the electrolysis activity of the electrolysis system or for a restart as efficiently as possible.

[0024] It can further be provided that the first fluid comprises nitrogen and the further fluid comprises deionized water.

[0025] By flushing with deionized water or fluid containing deionized water after a flushing process with nitrogen or nitrogen-containing fluid, a nitrogen concentration in the electrolysis system, in particular the cell stack of the electrolysis system, is minimized, so that an amount of fresh Hj-containing gas to be discarded during a restart is also minimized.

[0026] For this purpose, for example, the amount of Fh-containing gas to be discarded can be selected depending on an N2 concentration or an H2 concentration in the gas, or a predetermined period of time for which freshly produced Fh-containing gas is to be discarded can be selected to be correspondingly short, e.g. half as long as in an operation without the presented process.

[0027] It can further be provided that the first fluid and later the further fluid are passed simultaneously over the cell stack, connecting lines and the gas-liquid separator.

[0028] Alternatively, it can be provided that in a first rinsing step the first fluid is initially passed exclusively over the cell stack, then in a second rinsing step the further fluid is passed exclusively over the cell stack, and in a third rinsing step the further fluid is passed via connecting lines and finally over the gas-liquid separator.

[0029] By exclusively flushing the cell stack with the first fluid, safety requirements for the electrolysis system are met and nitrogen concentration in the electrolysis system is minimized

[0030] It can also be provided that the additional fluid is taken directly from the gas-liquid separator or is supplied via a supply line from an external system.

[0031] Since deionized water usually collects in the gas-liquid separators of a respective electrolysis system, this can be used to flush the electrolysis system after flushing with, for example, nitrogen or a nitrogen-containing fluid.

[0032] It can further be provided that the electrolysis system is divided into a plurality of separately flowable rinsing areas by means of at least one valve.

[0033] By having a plurality of separately flowable rinsing areas, the amount of fluid used to rinse a particular rinsing area can be adapted to the volume of a particular rinsing area and minimized accordingly.

[0034] It can further be provided that each flushing area is flowed through with the first fluid and / or the further fluid via a separate supply valve and / or discharge valve.

[0035] By means of a separate supply valve and / or discharge valve for a respective rinsing area, a spatially limited rinsing or a rinsing with a particularly high concentration of, for example, the first fluid can be carried out independently of the other rinsing areas.

[0036] According to a second aspect, the presented invention relates to an electrolysis system. The presented electrolysis system comprises at least one cell stack, at least one gas-liquid separator (usually at least one gas-liquid separator for the anode and cathode gases), a purge system, and a computing unit. The computing unit is configured to carry out a possible embodiment of the presented method.

[0037] It can be provided that the electrolysis system is divided into a plurality of rinsing areas, wherein each rinsing area can be flowed through by the first fluid and the at least further fluid via a separate supply valve and / or discharge valve.

[0038] Advantages provided for the method for operating an electrolysis system according to the first aspect of the invention also apply correspondingly to the electrolysis system according to the second aspect of the invention.

[0039] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

[0040] They show:

[0041] Fig. 1 shows a possible embodiment of the presented method,

[0042] Fig. 2 is a schematic representation of a possible design of the electrolysis system presented,

[0043] Fig. 3 is a schematic representation of another possible embodiment of the electrolysis system presented.

[0044] Description of the embodiments Fig. 1 shows a method 100 for operating an electrolysis system.

[0045] The method 100 comprises a maximization step 101 in which a fill level of one or both gas-liquid separators of the electrolysis system is maximized before an electrolysis activity of the electrolysis system is discontinued.

[0046] Furthermore, the method 100 comprises a rinsing step 103 in which at least one cell stack of the electrolysis system is rinsed with a first fluid and a further fluid different from the first fluid before the electrolysis activity of the electrolysis system is stopped.

[0047] Fig. 2 shows the hydrogen side of an electrolysis system 200, with a cell stack 201, a gas-liquid separator 203, a purge system with several purge valves 205, 207, 209, 211 and 213 as well as an optional pump 215 and a computing unit 217. In addition, the electrolysis system 200 comprises, not shown here, on the O2 side, another gas-liquid separator and possibly a pump, a heat exchanger and a filter / ion exchanger.

[0048] Fig. 2 shows an example of a cell stack 201. The inventive concept also encompasses electrolysis systems with multiple cell stacks, each connected to a common Fh-side or Oj-side gas-liquid separator.

[0049] The computing unit 217 is configured to control the flushing valves 205, 207, 209, 211 and 213 as well as the pump 215 such that the method 100 according to Fig. 1 runs.

[0050] The fill level of the gas-liquid separator 203 can be adjusted via valve 213. Valves 205, 207, 209, and 211 enable the flushing of lines or sections of lines and the safe disposal of respective fluids. Fig. 3 shows the hydrogen side of an electrolysis system 300, comprising a cell stack 301, a gas-liquid separator 303, a flushing system with several flushing valves 305, 307a, 307b, 309a, 309b, 311, and 313, as well as an optional pump 315 and a computing unit 317. Furthermore, the electrolysis system 399 (not shown here) comprises, on the O2 side, another gas-liquid separator, as well as, if appropriate, a pump, a heat exchanger, and a filter / ion exchanger.

[0051] The computing unit 317 is configured to control the flushing valves 305, 307a, 307b, 309a, 309b, 311 and 313 as well as the pump 315 such that respective flushing areas of the electrolysis system are flushed separately from one another and, if necessary, with a specific concentration of the first fluid or further fluid, and the fluids can be safely discarded.

Claims

Claims 1 . A method (100) for operating an electrolysis system (200, 300), the method (100) comprising: - maximizing (101) a fill level of a gas-liquid separator (203, 303) of the electrolysis system (200, 300) before an electrolysis activity of the electrolysis system (200, 300) is stopped, - Flushing (103) at least one cell stack (201, 301) of the electrolysis system (200, 300) with a first fluid and a further fluid different from the first fluid before the electrolysis activity of the electrolysis system (200, 300) is stopped.

2. Method (100) according to claim 1, characterized in that the maximizing and the purging are carried out for hydrogen-side lines and / or a hydrogen-side gas-liquid separator (203,303).

3. Method (100) according to claim 1 or 2, characterized in that the method (100) further comprises: - Determining a trigger condition that leads to the cessation of the electrolysis activity of the electrolysis system (200, 300).

4. Method (100) according to one of the preceding claims, characterized in that the first fluid comprises nitrogen and the further fluid comprises deionized water.

5. Method (100) according to one of the preceding claims, characterized in that that the first fluid and later the further fluid are passed simultaneously over the cell stack (201, 301), connecting lines and the gas-liquid separator (203, 303).

6. Method (100) according to one of claims 1 to 4, characterized in that in a first rinsing step the first fluid is initially passed exclusively over the cell stack (201, 301), then in a second rinsing step the further fluid is passed exclusively over the cell stack (201, 301), and in a third rinsing step the further fluid is passed via connecting lines and finally via the gas-liquid separator (203, 303).

7. Method (100) according to one of the preceding claims, characterized in that the further fluid is taken directly from the gas-liquid separator (203, 303) and / or is supplied via a supply line from an external system.

8. Method (100) according to one of the preceding claims, characterized in that the electrolysis system (200, 300) is divided into a plurality of separately flowable rinsing areas by means of at least one valve.

9. Method (100) according to claim 8, characterized in that each flushing area is flowed through with the first fluid and / or the further fluid via a separate supply valve and / or discharge valve.

10. Electrolysis system (200, 300), wherein the electrolysis system (200, 300) comprises: - a cell stack (201, 301), - a gas-liquid separator (203, 303), - a flushing system, and - a computing unit (217, 317), wherein the computing unit (217, 317) is configured to carry out a method (100) according to one of claims 1 to 9.

11. Electrolysis system (200, 300) according to claim 10, characterized in that the electrolysis system (200, 300) is divided into a plurality of rinsing regions, wherein each rinsing region can be flowed through by the first fluid and the further fluid via a separate supply valve and / or discharge valve.

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