Method for operating electrolysis system and electrolysis system

Abstract

The invention relates to a method for operating an electrolysis system (2) comprising at least one electrolysis cell (4) for producing hydrogen (6) and oxygen (8) as products, and at least two downstream compressors (10) for compressing at least one product (6, 8) produced in the electrolysis cell (4). In order to ensure that the partial-load operation of the electrolysis system (2) is optimized in terms of efficiency and still inexpensive, during the partial-load operation of the electrolysis cell (4), the compressors (10a) of the first group (A) are operated in a partial-load operation, while the one or more compressors (10b,... 10n) of the second group (B) are individually turned on or off in a full-load operation.

Description

Technical Field

[0001] The invention relates to a method for operating an electrolysis system comprising at least one electrolysis cell for producing hydrogen and oxygen as products and at least two downstream compressors for compressing at least one product produced in the electrolysis cell. The invention also relates to an electrolysis system suitable for carrying out the method. Background Art

[0002] An electrolysis system is a device that causes a material conversion (electrolysis) to occur by means of an electric current. There are many different electrochemical electrolysis processes, and accordingly there are also many different electrolysis systems, such as electrolysis systems for electrolyzing water.

[0003] Hydrogen is nowadays produced from water, for example, by means of proton exchange membrane (PEM) electrolysis or alkaline electrolysis. Electrolysis systems use electrical energy to produce hydrogen and oxygen from supplied water. The process takes place in an electrolysis stack consisting of a plurality of electrolysis cells. Water is introduced as a reactant into the electrolysis stack to which a direct current voltage (DC voltage) is applied, wherein, after passing through the electrolysis cells, a gas consisting of water and gas bubbles (O 2 and H 2 After liquid-gas separation, hydrogen and oxygen are obtained as products, which can be compressed in subsequent steps.

[0004] In alkaline electrolysis, usually a small number of stacks (1 or 2) are connected in series and form an electrolysis unit. In a PEM electrolyser, a plurality of stacks or modules are connected in series and form a module series. Several modules series here form an electrolysis unit.

[0005] In case of partial load operation of the electrolysis system, the partial load characteristics between the electrolyser and the downstream compressor are different. The partial load efficiency, mass flow and operating characteristics of the electrolyser are largely continuous. On the compression side, individual compressors are usually switched on / off for partial load mass flow and this may result in steps or jumps in efficiency. This is particularly a problem when the system size increases.

[0006] Expensive solutions to this problem include, for example, frequency-controlled drives for the compressor, which allow a continuous adaptation of the compressor power.

[0007] For example, document EP 0 085 285 A1 describes a compressor drive system for controlling the gas pressure in a compressed gas volume connected to a compressor. An alternating current drive is directly coupled to the compressor, which is driven at the same speed as the drive. The pressure in the gas volume is detected by a pressure detection device connected to a frequency converter. The frequency converter simultaneously changes the amplitude and frequency of the drive voltage supplied to the drive. This is done in response to changes in the pressure in the volume and thus forms a control loop.

[0008] The partial load characteristics of the compressor can be improved by a frequency converter and adjusted to the partial load characteristics of the electrolysis, however this solution is very costly. Summary of the invention

[0009] It is therefore an object of the present invention to ensure a partial load operation of an electrolysis system which is optimized with regard to efficiency and is also cost-effective.

[0010] According to the invention, this object is achieved by a method for operating an electrolysis system, comprising at least one electrolysis cell for producing hydrogen and oxygen as products, and at least two downstream compressors for compressing at least one product produced in the electrolysis cell, wherein, in partial load operation of the electrolysis cell, the compressors of a first group are operated in partial load operation, while one or more compressors of a second group are individually switched on or off in full load operation.

[0011] According to the invention, the object is also achieved by an electrolysis system suitable for carrying out the method, comprising at least one electrolysis cell for producing hydrogen and oxygen as products, at least two downstream compressors for compressing at least one product produced in the electrolysis cell, and a control unit for operating the compressors of a first group in partial load operation and one or more compressors of a second group individually in full load operation or switching them off.

[0012] The advantages and preferred embodiments listed below with respect to the method can be transferred to the electrolysis system to the same extent.

[0013] The invention is based on the idea that the design and control of the compressors can be adapted to load changes in the electrolysis process in a cost-effective manner by using not all compressors for part-load operation, but only some of the compressors forming a first group of compressors. The remaining compressors, which form a second group, are either operated at full load or switched off during part-load operation of the electrolysis system. Each group may comprise one or more compressors. If there are only two compressors in the system, one is assigned to the first group and the other to the second group.

[0014] The above method has the advantage that the compressors switched on in the second group can be operated at their optimum. Each compressor in the second group is controlled individually, i.e. independently of the other compressors in the second group. A high degree of flexibility is thus always ensured when adjusting the compression power to the partial load operation of the electrolysis system. In the case of a large number of compressors, these are arranged in particular in compressor units operating in parallel. Individual compressor units are switched on or off to optimize efficiency. This applies to all compressors, but is particularly relevant for the compressors of the second group. In this case, load changes can be achieved by only a part of the compressor units.

[0015] At the same time, the electrolyzers are operated with optimum efficiency to achieve the maximum overall system efficiency. The operator or the control unit can preselect the partial load of the electrolysis system according to the most efficient compressor operating point. This results in a relatively fine adjustment of the efficiency-optimized system operating point. As already described, the load change is performed by equipping a first group of compressors for partial load operation and switching on or off a second group of compressors. The change between different load points can be realized in a jumpy or continuous manner, wherein the continuous change is the preferred variant.

[0016] It is also useful to adapt the electrolysis cells and their process-engineering units to the compression according to their size and grouping, in particular to achieve their optimum efficiency at the efficiency-optimized compressor operating point. Since the compressor can also be operated closer to the efficiency-optimized operating point or at the efficiency-optimized operating point, the overall efficiency of the electrolysis system can thereby be improved.

[0017] According to a preferred embodiment, for the compressors of the first group, part-load operation is set by means of frequency-controlled drives. These compressors make it possible to smooth the possible compressor operating points or to adapt the electrolysis characteristics at part-load. Compared to alternative embodiments for implementing part-load operation, for example by closing valves (reducing the mass flow by opening / closing valves) or by varying the compressor capacity, the use of frequency-controlled drives is characterized by an optimal efficiency, i.e. a minimum energy consumption.

[0018] According to another preferred embodiment, the compressors are operated in parallel connection. In this way, products with particularly high mass flows can be compressed. Due to the parallel connection, compressor units are formed, wherein each unit can include one or more compressors.

[0019] With a view to a particularly cost-effective embodiment, the number of compressors of the first group is preferably smaller than the number of compressors of the second group. Only a minimum portion of the compressors or compressor units used are equipped with, for example, frequency-controlled drives for partial load operation of the compressors. At the same time, as many of the operating compressors as possible are operated at maximum efficiency (in full load operation) in order to reduce partial load losses.

[0020] Preferably, the first and second sets of compressors are used to compress only the produced hydrogen, since hydrogen is the main product of the electrolysis process and its compression is always advantageous.

[0021] Advantageously, the compressor is a piston compressor and / or a screw compressor, since this type of compressor is best suited to the load range of the mass flows occurring in the electrolysis process. DETAILED DESCRIPTION

[0022] An embodiment of the present invention is explained in more detail with reference to the accompanying drawings. Here, the only accompanying drawing shows an electrolysis system 2, which includes an electrolyzer 4 for producing products, namely hydrogen 6 and oxygen 8. Each product stream 6, 8 undergoes a gas pretreatment shown by box 12. Gas pretreatment refers to the catalysis of impurity gases, wherein the residual oxygen in the hydrogen stream reacts thermally with the oxygen, and vice versa on the oxygen side. The corresponding product gas is then usually dried and cooled if necessary. The product can then be first stored in a gas container 14 or can be directly compressed by a plurality of downstream compressors 10.

[0023] The electrolyzer 4 is, for example, a proton exchange membrane (PEM) electrolyzer or an alkaline electrolyzer. Alternatively, it may be, for example, an anion exchange membrane (AEM) electrolyzer. The electrolyzer 4 in the figure specifically represents a plurality of electrolysis units connected in series or in parallel.

[0024] Two or more compressors 10 (10 a , 10 b , ... 10 n , where n≥2). They are connected in parallel to form a so-called unit. In the figure, each compressor unit is equipped with only one compressor 10 a , 10 b ,……10 n , but these units may optionally also comprise two or more compressors. It is also conceivable that the compressor 10 a , 10 b , ... 10 n of series connection and any combination of parallel connection and series connection and this depends on the requirements of the electrolysis system 2.

[0025] Each compressor 10 is equipped with a driver 16. At least one compressor 10a There is also a frequency-controlled drive 18 (Variable Frequency Drive in English), which includes a frequency converter. The frequency-controlled drive 18 enables a freely variable speed control by means of an induction drive operated by three-phase alternating current. On the corresponding product side, one or more compressors 10 with a frequency-controlled drive 18 a In the embodiment shown, the remaining compressors 10 b ...10 n A second group B is formed.

[0026] The compressed products, hydrogen 6 and oxygen 8 , are finally pre-treated in step 20 and discharged from the electrolysis system 2 .

[0027] The electrolysis system 2 also has a control unit symbolically represented by a block 22. The control unit 22 controls the compressor 10 based on data from the electrolysis cell 4. a , 10 b , ... 10 n Drive 16.

[0028] In some cases, the load of the electrolyzer 4 may be lower than its full load, i.e. the electrolyzer 4 is operated in a partial load operation mode. In this case, the control unit 22 controls the compressors 10 of the first group A so that they also operate at partial load, while the compressors 10 of the second group B are turned on or off individually, i.e. independently of each other. When the compressors 10 of the second group B are turned on, they operate at full load. When designing the electrolysis system 2, the efficiency optimum values ​​of the system components are coordinated with each other, i.e. the number of compressors 10 is adjusted to be especially adapted to the number of electrolysis units, so that the entire system can be operated with optimized efficiency.

[0029] In the figure, for each of the two product sides, a compressor 10 is shown. a , 10 b , ... 10 n The division into two groups A, B. However, it is also conceivable to equip one or more compressors 10a with a frequency-controlled drive 18 only for one product, in particular on the hydrogen product side.

Claims

1. A method for operating an electrolysis system (2), comprising at least one electrolysis cell (4) for producing hydrogen (6) and oxygen (8) as products, and at least two downstream compressors (10) for compressing at least one product (6, 8) produced in the electrolysis cell (4), wherein: In partial load operation of the electrolyzer (4), the compressor (10) of the first group (A) a ) is operated in a part-load mode, and one or more compressors (10 b , ... 10 n ) can be turned on or off individually in full load operation.

2. The method according to claim 1, wherein: For the compressors (10) of the first group (A), the part-load operation is set by a frequency-controlled drive (18).

3. A method according to any one of the preceding claims, wherein: The compressors (10) are operated in parallel connection.

4. A method according to any one of the preceding claims, wherein: The compressor (10) of the first group (A) a ) is less than the number of compressors (10) of the second group (B) b , ... 10 n ) quantity.

5. A method according to any one of the preceding claims, wherein: The compressors (10) of the first group (A) and the second group (B) are used to compress only the produced hydrogen (6).

6. An electrolysis system (2) suitable for carrying out the method according to claim 1, comprising at least one electrolysis cell (4) for producing hydrogen (6) and oxygen (8) as products, at least two downstream compressors (10) for compressing at least one product (6, 8) produced in the electrolysis cell (4), and a control unit (22) for operating the compressors (10) of a first group (A) at a partial load in operation of the electrolysis cell (4). a ) is operated in a part load mode and one or more compressors (10 b , ... 10 n ) can be turned on or off individually in full load operation.

7. The electrolysis device according to claim 6, wherein: The compressor (10) is a piston compressor and / or a screw compressor.

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