Method for compressing hydrogen and compressor assembly

Abstract

The invention relates to a compressor assembly and a method for compressing hydrogen produced by means of an electrolysis cell, in which hydrogen is compressed to an intermediate pressure (20) by means of a first liquid ring machine (15), and in which hydrogen is compressed from the intermediate pressure (20) to a discharge pressure by means of a second liquid ring machine (25, 35, 41, 42, 43, 44, 45). A pressure equalization between the outlet side (21) and the inlet side (22) of the first liquid ring machine (15) is permitted by the bypass line (16). The input pressure (18) on the inlet side (22) of the first liquid ring machine (15) is kept constant by changing the cross-section of the bypass line (16) by means of an adjustable valve (17). The hydrogen is compressed from the intermediate pressure (20) to the discharge pressure without keeping the intermediate pressure (20) constant.

Description

Technical Field

[0001] This invention relates to a method for compressing hydrogen gas generated by an electrolyzer and a compressor assembly. Background Technology

[0002] Hydrogen produced by electrolysis is typically highly compressed for storage or transport, for example, to pressures between 600 and 700 bar above atmospheric pressure. This invention relates to initial compression from the pressure at which the hydrogen leaves the electrolyzer up to a discharge pressure that is higher and, for example, on the order of 5 to 10 bar above atmospheric pressure. To achieve significantly higher final pressures, additional compression stages may be subsequently applied, such as reciprocating compressors.

[0003] For trouble-free operation of the electrolyzer, it is advantageous to keep the input pressure constant at which hydrogen is delivered from the electrolyzer to the compressor assembly.

[0004] Advantageously, components made of liquid ring compressors are used for the initial compression of hydrogen. Liquid ring compressors are well-suited for conveying aqueous mixtures discharged from electrolyzers and are less expensive to manufacture than, for example, reciprocating compressors. However, liquid ring compressors have historically had poor energy efficiency, especially when operating at partial loads, which is common in electrolyzers used to utilize solar or wind power. There are often prolonged operating phases during which the electrolyzer's power output is significantly below maximum. Summary of the Invention

[0005] This invention is based on the objective of providing a method and compressor assembly for compressing hydrogen produced by an electrolyzer, thereby avoiding these drawbacks. This objective is achieved by means of the features of the independent claims. Advantageous embodiments are given in the dependent claims.

[0006] In the method according to the invention for compressing hydrogen generated by an electrolyzer, the hydrogen is compressed to an intermediate pressure using a first liquid ring compressor. The hydrogen is then compressed from the intermediate pressure to the discharge pressure using a second liquid ring compressor. Backflow from the output side to the inlet side of the first liquid ring compressor is permitted via a bypass line. The input pressure on the inlet side of the first liquid ring compressor is kept constant by changing the cross-section of the bypass line using an adjustable valve.

[0007] In one embodiment, hydrogen is compressed from the intermediate pressure to the discharge pressure without maintaining a constant intermediate pressure. The input pressure of the first liquid ring compressor is regulated by adjusting an adjustable valve in the bypass line. Since the second liquid ring compressor is not equipped with a bypass regulating device and therefore cannot respond quickly to changes in intermediate pressure, the intermediate pressure drops when the bypass valve of the first liquid ring compressor opens. During operation of the compressor assembly, the fluctuation of the intermediate pressure can be greater than 0.1 bar, preferably greater than 0.2 bar, and more preferably greater than 0.5 bar. The fluctuation of the intermediate pressure refers to the difference between the highest and lowest values ​​of the intermediate pressure during continuous operation of the compressor assembly composed of the first and second liquid ring compressors. This fluctuation is particularly a consequence of the fluctuating volumetric flow supplied from the electrolyzer to the compressor assembly.

[0008] This invention departs from conventional practices, where pressure on the input side of the liquid ring compressor is regulated via a bypass line even when the pressure on the output side remains constant. In two liquid ring compressors connected in series, this typically means that the second liquid ring compressor also has a bypass line, through which backflow from the output side of the second liquid ring compressor to the input side is achieved.

[0009] The present invention has recognized that the backflow through the bypass line of the second liquid ring machine is a major reason for the poor energy efficiency of the series connection structure of the liquid ring machine; and in the case of the first liquid ring machine, even if the pressure on the output side of the first liquid ring machine is subject to fluctuations, it is possible to regulate the pressure when compressing hydrogen through the bypass line.

[0010] An adjustable valve is arranged in the bypass line, which regulates the backflow from the output side to the input side of the first liquid ring machine. This adjustable valve can be continuously adjusted between an open and closed state. The adjustable valve can be connected to a regulating circuit in which the valve's on / off state is adjusted according to the pressure on the input side of the first liquid ring machine. The regulating circuit can be configured such that as the pressure on the input side of the first liquid ring machine increases, the adjustable valve further closes; and vice versa.

[0011] A buffer container may be arranged between the discharge section of the first liquid ring machine and the inlet section of the second liquid ring machine. The buffer container can attenuate short-term fluctuations in intermediate pressure. The buffer container may, for example, have a volume between 0.2 cubic meters and 5 cubic meters, preferably between 0.5 cubic meters and 2 cubic meters. This buffer container can also function as a liquid separator to separate a quantity of liquid contained in the volumetric flow from the first liquid ring machine. The separated liquid can be directed back to the first liquid ring machine, particularly the liquid rings returned to the first liquid ring machine.

[0012] A check valve can be installed between the discharge section of the first liquid ring compressor and the inlet section of the second liquid ring compressor to prevent pressure rise in the second liquid ring compressor from acting against the intermediate pressure. The check valve can be located between a branch leading to a bypass line and the inlet section of the second liquid ring compressor. A check valve can also be located between a buffer container and the inlet section of the second liquid ring compressor. However, especially when multiple liquid ring compressors are connected in parallel in the second stage, this check valve allows for the shutdown of multiple individual machines to match power to demand.

[0013] In one implementation, a preset upper limit is set for the intermediate pressure. Excessively high intermediate pressures are disadvantageous because the first liquid ring compressor may no longer be able to maintain a constant pressure on the input side. This, in turn, can adversely affect the electrolyzer, as hydrogen can be delivered to the first liquid ring compressor at a specific pressure. Alternatively, a liquid ring compressor, optimized for lower discharge pressures but limited in maximum discharge pressure, can also be used for the first compression stage. The second liquid ring compressor can be designed and operated such that it does not exceed the upper limit for the intermediate pressure. In particular, the second liquid ring compressor can be operated with an increased rotational speed to offset any increase in intermediate pressure exceeding the upper limit.

[0014] According to one understanding of the invention, it can be advantageous not to keep the intermediate pressure constant. A decrease in intermediate pressure results in energy savings in the first stage, but it must be ensured that the intermediate pressure does not fall too low in order to retain a regulation margin for bypass control and also to avoid cavitation (or water vaporization) in the second compressor. If the bypass line of the first liquid ring compressor is opened, this quickly leads to a drop in intermediate pressure. This drop can only be compensated for with a certain delay by reducing the speed of the second liquid ring compressor. Since the intermediate pressure must not fall below a minimum value, and the liquid ring compressor always requires a minimum speed to build a stable liquid ring, but these two values ​​are also correlated, therefore, when two liquid ring compressors are connected in series, they have so far always operated at a constant intermediate pressure.

[0015] One possibility for maintaining a constant intermediate pressure is that the second liquid ring compressor also has a bypass line that allows backflow from the output side to the input side of the second liquid ring compressor. By coordinating the operation of the two bypass lines, the intermediate pressure can be maintained at a preset value. This is not included within the scope of the invention because a bypass line on the second liquid ring compressor would impair the energy efficiency of the compressor assembly. The compression of hydrogen from the intermediate pressure to the discharge pressure can be performed without allowing backflow through the reflux line arranged between the discharge and inlet sides of the second liquid ring compressor.

[0016] The second liquid ring compressor can be operated in such a way that energy consumption remains low without exceeding the upper limit for the intermediate pressure. This approach can be limited by adhering to the permissible operating range of the second liquid ring compressor. Specifically, a lower limit for the speed of the second liquid ring compressor can be set. This lower limit can be guided by the operating requirements of the second liquid ring compressor. The lower limit can be determined in such a way that undesirable vibrations in the second liquid ring compressor are avoided. The overall function of the compressor components is not impaired by the lower speed limit because when the second liquid ring compressor operates at a higher speed than required to maintain the intermediate pressure, this can be compensated for by more forcefully opening the valves in the bypass line of the first liquid ring compressor.

[0017] Energy efficiency can be further improved by using multiple second liquid ring compressors connected in parallel to compress hydrogen from the intermediate pressure to the discharge pressure. This opens up the additional possibility of varying the number of second liquid ring compressors used to compress the intermediate pressure to the discharge pressure. It is generally more energy efficient to keep only that portion of the second liquid ring compressors running and shut down the rest if the power of a portion of the second liquid ring compressors is sufficient to maintain the intermediate pressure within the desired range. In particular, a portion of the second liquid ring compressors can be shut down based on the instantaneous power of the electrolyzer, and the volumetric flow from the electrolyzer through the first liquid ring compressor can be compressed using another portion of the second liquid ring compressors.

[0018] The compression of hydrogen from the intermediate pressure to the output pressure can be carried out using at least two, preferably at least three, and more preferably at least five second liquid ring compressors connected in parallel. The number of liquid ring compressors subjected to temporary shutdown can be variable. There can be operating states in which a single liquid ring compressor is shut down, and in which only one liquid ring compressor is operating. All operating states in between are also possible.

[0019] The control of the second compression stage, i.e., one or more second liquid ring compressors, can be performed using open-loop control or closed-loop regulation. Control can be based on the power output of the electrolyzer, the position of the adjustable valve in the bypass line of the first liquid ring compressor, the intermediate pressure, the speed of the first liquid ring compressor, and / or other parameters of the compressor components. Control can be performed such that a table is stored in the control unit responsible for the second compression stage, from which preset values ​​for the operation of the second compression stage can be read based on measurements of the current operating status of the compressor components and, in particular, the power output of the electrolyzer. The control unit can be designed to send control commands to one or more second liquid ring compressors to adjust their operation according to the preset values ​​in the table. The preset values ​​can be estimated based on the state of the compressor components or based on digital twin simulation. In the case of a closed-loop regulation, the preset values ​​can be determined directly from measurements of the operating status of the compressor components.

[0020] Predictive open-loop control or closed-loop regulation can also be implemented, incorporating predictions of the future operating state of the electrolyzer. Here, predictions of the expected amount of renewable energy at future points in time can be considered. Expectations regarding the future amount of wind or solar energy can, for example, be derived from weather forecasts.

[0021] The pressure at which hydrogen is released from the electrolyzer can be slightly higher than atmospheric pressure, for example, between 0.1 bar and 0.3 bar higher than atmospheric pressure. The intermediate pressure between the first and second compression stages can, for example, be between 0.5 bar and 2 bar higher than atmospheric pressure. The discharge pressure on the output side of the second compression stage can, for example, be between 6 bar and 12 bar higher than atmospheric pressure. One or more additional compression stages can be connected to the second compression stage, by means of which the hydrogen is compressed to a pressure at least 100 bar, preferably at least 200 bar, and more preferably at least 500 bar higher than atmospheric pressure. A liquid separator can be arranged between the second and third compression stages to separate a liquid quantity contained in the volumetric flow from the second liquid ring machine. The separated liquid quantity can be directed back to the second liquid ring machine, particularly the liquid ring directed back to the second liquid ring machine.

[0022] The compressor assembly can be designed to deliver a high volumetric flow of hydrogen from the electrolyzer to the first liquid ring machine. For example, the first liquid ring machine can be designed to receive a volumetric flow of at least 2,000 cubic meters per hour from the electrolyzer, preferably at least 5,000 cubic meters per hour, and more preferably at least 10,000 cubic meters per hour.

[0023] The volumetric flow rate of hydrogen discharged from the electrolyzer typically depends on the extent to which regenerative energy is available for the operation of the electrolyzer. Since the amount of available regenerative energy is known to vary considerably, it is advantageous that the compressor assembly is designed to deliver a highly fluctuating volumetric flow rate. The compressor assembly can be operated such that the maximum volumetric flow rate is invoked at less than 20%, preferably less than 10%, and more preferably less than 5% of the operating time. During other phases of the operating time, a smaller volumetric flow rate, less than 50%, preferably less than 20%, and more preferably less than 10%, can be delivered. The operating time for which the smaller volumetric flow rate is delivered can account for at least 10%, preferably at least 20%, and more preferably at least 50% of the total operating time.

[0024] In the second compression stage, adaptation to the fluctuating volumetric flow can be achieved by changing the number of second liquid ring machines put into operation.

[0025] In the first compression stage, the compressor assembly may include exactly one liquid ring compressor. A rapid response to varying volumetric flow from the electrolyzer to the input of the first liquid ring compressor can be achieved by adapting the cross-section of the bypass line. However, when there is strong backflow through the bypass line at low volumetric flow rates in the electrolyzer, it is detrimental to energy efficiency.

[0026] By adapting the cross-section of the bypass pipeline, the pressure on the inlet side of the first liquid ring mill can be kept constant by allowing the first liquid ring mill to operate at a variable speed. During the operation phase when the volumetric flow rate from the electrolyzer is low, the speed of the first liquid ring mill can be reduced, thereby consuming less energy. However, operating limits for the first liquid ring mill should be followed; for example, by adhering to a lower speed limit below which stable operation of the first liquid ring mill is no longer guaranteed.

[0027] Starting from a first liquid ring compressor capable of delivering a volumetric flow rate up to 10,000 cubic meters per hour, this compressor assembly can be used to operate electrolyzers with a power output up to approximately 50 megawatts. For electrolyzers with even higher power outputs, multiple compressor assemblies can be operated in parallel. This opens up the possibility of further improving energy efficiency by varying the number of compressor assemblies used to compress hydrogen from the electrolyzer.

[0028] The present invention includes a compression system in which multiple compressor assemblies of the type described above are connected to an electrolyzer. The compression system can be operated such that the number of compressor assemblies used to compress hydrogen is varied according to the volumetric flow supplied from the electrolyzer to the compressor assemblies.

[0029] The present invention also relates to a compressor assembly for compressing hydrogen produced by an electrolyzer, the compressor assembly including a first liquid ring compressor for compressing hydrogen supplied from the electrolyzer to an intermediate pressure; and the compressor assembly including a second liquid ring compressor for compressing the hydrogen from the intermediate pressure to a discharge pressure. A bypass line is provided between the output side and the inlet side of the first liquid ring compressor to maintain a constant input pressure on the inlet side of the first liquid ring compressor. The compressor assembly is designed to compress hydrogen from an intermediate pressure to a discharge pressure without maintaining a constant intermediate pressure.

[0030] This disclosure includes improvements to compressor assemblies having features described in relation to the method according to the invention. This disclosure includes improvements to the method described in relation to the compressor assembly according to the invention. Attached Figure Description

[0031] The invention will now be described by way of example with reference to the accompanying drawings and advantageous embodiments. In the drawings: Figure 1 A compressor assembly according to the invention is shown, designed for performing the method according to the invention; Figure 2 Showing according to Figure 1 A view in an alternative embodiment of the present invention; Figure 3 An alternative embodiment of the compressor assembly according to the present invention is shown; Figure 4 A compressor system with multiple compressor components according to the invention is shown. Detailed Implementation

[0032] exist Figure 1 A compressor assembly connected to an electrolyzer 14 is shown. Hydrogen produced in the electrolyzer 14 is delivered to the compressor assembly at an input pressure (which may be, for example, 0.2 bar above atmospheric pressure). In the compressor assembly, the hydrogen is compressed and discharged through an output line 32 at a discharge pressure (e.g., 10 bar above atmospheric pressure). The electrolyzer 14 has a maximum power of 25 megawatts, which corresponds to a hydrogen volume flow on the order of 5,000 cubic meters per hour supplied to the input of the compressor assembly.

[0033] For the operation of electrolyzer 14, it is important to maintain a constant pressure at the output of electrolyzer 14 so that the generated hydrogen can be delivered to the compressor assembly at that pressure.

[0034] The compressor assembly includes a first compression stage with a first liquid ring compressor 15 and a second compression stage with a second liquid ring compressor 25. The first liquid ring compressor 15 and the second liquid ring compressor 25 are connected in series. Hydrogen is compressed from an initial pressure to an intermediate pressure 20 by means of the first liquid ring compressor 15, which may be, for example, between 0.5 bar and 2 bar above atmospheric pressure. Hydrogen is then compressed from the intermediate pressure 20 to a final pressure by means of the second liquid ring compressor 25.

[0035] The first liquid ring machine 15 is driven by a motor 23, which operates at a constant speed in this embodiment. A bypass line 16 extends between the discharge side 21 and the inlet side 22 of the first liquid ring machine 15, allowing backflow from the discharge side 21 to the inlet side 22. The bypass line 16 is provided with a continuously adjustable valve 17. The cross-section of the bypass line 16 is changed by means of the adjustable valve 17, which is available for backflow from the discharge side 21 to the inlet side 22.

[0036] Adjustable valve 17 is controlled by a control unit (not shown), and the control is based on the input pressure 18 applied to the input side 22 of the first liquid ring machine 15. The control unit is designed to keep the input pressure 18 constant. The control unit thus controls adjustable valve 17 such that an increase in input pressure is offset by increasing the cross-section of bypass line 16; and a decrease in input pressure is offset by decreasing the cross-section of bypass line 16.

[0037] A buffer container 19 with a volume of 0.5 cubic meters is arranged between the first liquid ring machine 15 and the second liquid ring machine 25. The buffer container 19 attenuates fluctuations in the intermediate pressure 20 caused by the operation of the adjustable valve 17. The buffer container 19 also functions as a liquid separator, by means of which a certain amount of liquid is separated from the volumetric flow from the first liquid ring machine 15. The liquid is then guided back to the liquid ring of the first liquid ring machine 15 via the heat exchanger 24.

[0038] The second liquid ring compressor 25 (with intermediate pressure 20 applied at the inlet 33) is driven by a variable-speed motor 28, which is powered by a converter (or frequency converter, i.e., Umrichter) 29 to adjust to the desired speed. Between the discharge side 26 of the second liquid ring compressor 25 and the output line 32 of the compressor assembly, a volumetric flow is guided through a liquid separator 30. The amount of liquid separated from the volumetric flow is guided back to the liquid ring of the second liquid ring compressor 25 via a heat exchanger 27.

[0039] The control unit operates the inverter 29 in such a way that, on the one hand, the intermediate pressure 20 is maintained within a range between 0.5 bar and 2 bar above atmospheric pressure, and on the other hand, energy consumption is kept as low as possible. Here, the control unit considers the operating limits of the second liquid ring machine 25 and, for example, prevents the speed from dropping to a level that would cause the second liquid ring machine 25 to vibrate. The control unit reads relevant control commands for the inverter 29 from a table storing control commands related to parameters such as the power of the electrolyzer 14, the position of the adjustable valve 17, and the intermediate pressure 20.

[0040] This means for the operation of the compressor assembly that the adjustable valve 17 operates only according to the input pressure 18 and tolerates fluctuations in the intermediate pressure 20 that result from the operation of the adjustable valve 17. The speed regulation of the second liquid ring compressor 25 offsets the fluctuations in the intermediate pressure 20, but does not fully compensate for them. The effect of the adjustable valve 17 on the intermediate pressure 20 is significantly faster than the subsequent change in the speed of the second liquid ring compressor 25. However, the speed regulation of the second liquid ring compressor 25 is sufficient to maintain the intermediate pressure 20 within a preset range, which may be, for example, between 0.5 bar and 2 bar above atmospheric pressure.

[0041] If the second liquid ring compressor 25 operates at a higher speed than required to maintain the intermediate pressure 20, the reduced intermediate pressure 20 results in the first liquid ring compressor 15 being able to deliver a higher volumetric flow, which in turn leads to a further opening of the adjustable valve 17 due to the reduced input pressure 18. Therefore, the higher speed of the second liquid ring compressor 25 only results in higher energy consumption without damaging the electrolyzer 14 due to changes in the input pressure 18. In this context, the converter 29 is operated such that the speed of the second liquid ring compressor 25 is kept as low as permitted by the operating conditions of the compressor components.

[0042] exist Figure 2 An alternative embodiment is shown in which the electrolyzer 14 has a maximum power of 50 megawatts, corresponding to a volumetric flow rate of approximately 10,000 cubic meters per hour of hydrogen. A first liquid ring compressor 15 capable of delivering this volumetric flow rate is provided on the first compression stage. The second compression stage includes two second liquid ring compressors 25 and 35 operating in parallel with each other.

[0043] The additional compression stage is connected to the output line 32 of the compressor assembly, and the additional compression stage is... Figure 2 The hydrogen is schematically represented by box 36. The additional compression stage 36 compresses the hydrogen from a pressure 10 bar above atmospheric pressure in the output line 32 to a significantly higher pressure, such as 700 bar. The hydrogen is then stored at this pressure in tank 37.

[0044] The two second liquid ring compressors 25, 35 in the second compression stage are driven by motors 28, 38, whose speeds are variablely controlled by converters 29, 39. If the power of the electrolyzer 14 is close to its maximum power, the two second liquid ring compressors 25, 35 operate in parallel with each other and according to the combined... Figure 1 The same principles are used to operate as described in the embodiments.

[0045] In the electrolyzer 14 fed by renewable energy, there exists a prolonged operating phase during which the power output is significantly lower than the maximum power output, for example, 20% or 10% of the maximum power output. By connecting two second liquid ring compressors 25, 35 in parallel on the second compression stage, another possibility for improving energy efficiency is opened up by shutting down one of the two second liquid ring compressors 25, 35 and using only the other two second liquid ring compressors to deliver a reduced volumetric flow.

[0046] The ability to keep only a portion of the second liquid ring compressors 25 and 35 operational provides the control unit with additional degrees of freedom that can be used to improve energy efficiency. Instead of operating both second liquid ring compressors 25 and 35 at extremely low speeds, one of the two second liquid ring compressors 25 and 35 operates at a higher speed. The control unit reads relevant control commands from a table based on parameters relating to the operating status of the compressor components (particularly based on the instantaneous power of the electrolyzer 14).

[0047] Additionally, the first liquid ring compressor 15 of the first compression stage is also driven by variable-speed drives 23, 34. Instead of tolerating high backflow through the bypass line 16 under low volumetric flow conditions from the electrolyzer 14, the speed of the first liquid ring compressor 15 can be reduced. This results in higher energy efficiency because the backflow through the bypass line 16 is reduced. The control unit accordingly operates the adjustable valve 17 and the inverter 34, wherein the operation can be performed according to different parameters of the operating state, especially according to the instantaneous power of the electrolyzer 14.

[0048] exist Figure 3 A compressor assembly 40 is shown, which includes a single liquid ring compressor 15 on a first compression stage 46 and five second liquid ring compressors 41, 42, 43, 44, 45 connected in parallel on a second compression stage 47. With multiple second liquid ring compressors 41, 42, 43, 44, 45 that can be independently switched on or off, it is possible to more precisely coordinate the compression power provided on the second compression stage 47 with the instantaneous power of the electrolyzer.

[0049] exist Figure 4In this process, electrolyzer 14 has a higher maximum power, for example, 250 megawatts. To enable the delivery of a volumetric flow of hydrogen produced by the electrolyzer, a compressor system is connected to electrolyzer 14, in which five... Figure 3 The compressor assemblies 40 shown operate in parallel with each other. By enabling the compressor assemblies 40 to be turned on or off individually, or by enabling the liquid ring compressors of the second compression stage 47 in each compressor assembly to be turned on or off individually, the compressor system can be more precisely coordinated with the current power of the electrolyzer 14, which can achieve further improvements in energy efficiency.

Claims

1. A method for compressing hydrogen gas generated by an electrolyzer, wherein, Hydrogen is compressed to an intermediate pressure (20) by means of a first liquid ring compressor (15), and wherein the hydrogen is compressed from the intermediate pressure (20) to the discharge pressure by means of a second liquid ring compressor (25, 35, 41, 42, 43, 44, 45), wherein a bypass line (16) allows backflow between the output side (21) and the inlet side (22) of the first liquid ring compressor (15), wherein the input pressure (18) on the inlet side (22) of the first liquid ring compressor (15) is kept constant by means of an adjustable valve (17) to change the cross-section of the bypass line (16), and wherein the hydrogen is compressed from the intermediate pressure (20) to the discharge pressure without keeping the intermediate pressure (20) constant.

2. The method according to claim 1, wherein, An adjustable valve (17) is arranged in the bypass line (16) to regulate the backflow from the output side (21) to the input side (22) of the first liquid ring machine (15).

3. The method according to claim 1 or 2, wherein, A buffer container (19) is arranged between the output side (21) of the first liquid ring machine (15) and the inlet (33) of the second liquid ring machine (25), the buffer container having a volume between 0.2 cubic meters and 5 cubic meters, preferably between 0.5 cubic meters and 2 cubic meters.

4. The method according to any one of claims 1 to 3, wherein, The intermediate pressure (20) is preset with an upper limit, and the second liquid ring machine (25) is operated such that it does not exceed the upper limit for the intermediate pressure (20).

5. The method according to any one of claims 1 to 4, wherein, The hydrogen gas is compressed from the intermediate pressure (20) to the discharge pressure by means of multiple second liquid ring machines (25, 35, 41, 42, 43, 44, 45), and the second liquid ring machines (25, 35, 41, 42, 43, 44, 45) are connected in parallel with each other.

6. The method according to claim 5, wherein, Based on the instantaneous power of the electrolytic cell (14), a portion of the second liquid ring machine (25,35,41,42,43,44,45) is shut off, and the volumetric flow from the electrolytic cell (14) via the first liquid ring machine (15) is compressed by the other portion of the second liquid ring machine (25,35,41,42,43,44,45).

7. The method according to any one of claims 1 to 6, wherein, Hydrogen is compressed from an input pressure (18) to an intermediate pressure (20) by means of the first liquid ring compressor (15), the input pressure being between 0.1 bar and 0.3 bar higher than atmospheric pressure, and the intermediate pressure being between 0.5 bar and 2 bar higher than atmospheric pressure.

8. The method according to any one of claims 1 to 7, wherein, Hydrogen is compressed to a discharge pressure, which is between 6 and 12 bar higher than atmospheric pressure, by means of one or more second liquid ring machines (25, 35, 41, 42, 43, 44, 45).

9. The method according to claim 8, wherein, The hydrogen is compressed to a pressure of at least 100 bar, preferably at least 200 bar, and more preferably at least 500 bar above atmospheric pressure by means of one or more subsequent compression stages (36).

10. The method according to any one of claims 1 to 9, wherein, The first liquid ring machine (15) is designed to receive a volume flow of at least 2,000 cubic meters per hour from the electrolytic cell (14), preferably at least 5,000 cubic meters per hour, and more preferably at least 10,000 cubic meters per hour.

11. The method according to any one of claims 1 to 10, wherein, The first liquid ring machine (15) operates at a variable speed.

12. A compressor assembly for compressing hydrogen produced by means of an electrolyzer, the compressor assembly having a first liquid ring compressor (15) for compressing hydrogen supplied from an electrolyzer (14) to an intermediate pressure (20); the compressor assembly having a second liquid ring compressor (25, 35, 41, 42, 43, 44, 45) for compressing the hydrogen from the intermediate pressure (20) to a discharge pressure; and the compressor assembly having a bypass line (16) between the output side (21) and the inlet side (22) of the first liquid ring compressor (15) for keeping the input pressure (18) on the inlet side (22) of the first liquid ring compressor (15) constant, wherein, The compressor assembly is designed to compress the hydrogen from the intermediate pressure (20) to the discharge pressure without keeping the intermediate pressure (20) constant.

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