Method for operating an electrolysis system, and electrolysis system

Abstract

The invention relates to a method for operating an electrolysis system (2) comprising at least one electrolyser (4) for generating 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 electrolyser (4). In order to ensure part-load operation of the electrolyser (2) that is optimised in terms of efficiency and is also cost-effective, during part load operation of the electrolyser (4), a first group (A) of compressors (10a,) is operated in part-load operation, while the compressor(s) (10b,...10n) of a second group (B) can be switched on or off individually for full-load operation.

Description

[0001] Description

[0002] Method for operating an electrolysis plant and electrolysis plant

[0003] The invention relates to a method for operating an electrolysis plant comprising at least one electrolyzer for producing hydrogen and oxygen as products, and at least two downstream compressors for compressing at least one product produced in the electrolyzer. The invention further relates to an electrolysis plant suitable for carrying out the method.

[0004] An electrolysis plant is a device that uses electrical current to transform substances (electrolysis). Due to the variety of different electrochemical electrolysis processes, there are also a variety of electrolysis plants, such as an electrolysis plant for water electrolysis.

[0005] Nowadays, hydrogen is produced from water using, for example, proton exchange membrane (PEM) electrolysis or alkaline electrolysis. The electrolysis plants use electrical energy to produce hydrogen and oxygen from the supplied water. This process takes place in an electrolysis stack made up of several electrolysis cells. Water is introduced as the reactant into the electrolysis stack, which is subjected to direct current (DC voltage). After passing through the electrolysis cells, two fluid streams consisting of water and gas bubbles (O2 and H2 respectively) emerge. After a liquid-gas separation, the products hydrogen and oxygen are obtained, which can be compressed in a subsequent step.

[0006] In alkaline electrolysis, a few stacks (1 or 2) are usually connected in series to form an electrolysis unit. In a PEM electrolyzer, several stacks or modules are connected in series to form a module row. Several module rows form an electrolysis unit.

[0007] When the electrolysis plant is operating at partial load, the partial load behavior differs between the electrolyzers and the downstream compressors. Electrolyzers exhibit a largely continuous progression of partial load efficiency, mass flow, and operating behavior. On the compression side, individual compressors are typically switched on / off for partial load mass flows, and this can lead to steps or jumps in efficiency. This problem arises particularly with increasing plant sizes.

[0008] To solve the problem, costly options such as frequency-controlled drives for the compressors are available, which allow continuous adjustment of the compressor performance.

[0009] A compressor drive system for controlling the gas pressure in a compressed gas volume connected to the compressor is described, for example, in EP 0 085 285 A1. An AC 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 pressure sensing means connected to a frequency converter. The converter simultaneously changes the amplitude and frequency of the drive voltage supplied to the drive. This occurs in response to pressure changes in the volume, thus forming a control loop.

[0010] Using a frequency converter, the partial load behavior of the compressors can be improved and adapted to the partial load behavior of the electrolysis, but this solution is associated with very high costs.

[0011] The invention is therefore based on the object of ensuring part-load operation of the electrolysis plant which is optimized with regard to efficiency and which is also cost-effective. This object is achieved according to the invention by a method for operating an electrolysis plant comprising at least one electrolyzer for producing hydrogen and oxygen as products, and at least two downstream compressors for compressing at least one product produced in the electrolyzer, wherein in part-load operation of the electrolyzer a first group of compressors is operated in part-load operation, while the compressor or compressors of a second group are individually switched on or off in full-load operation.

[0012] The object is further achieved according to the invention by an electrolysis plant which is suitable for carrying out the method, comprising at least one electrolyzer for producing hydrogen and oxygen as products, as well as at least two downstream compressors for compressing at least one product produced in the electrolyzer, as well as a control unit which is designed to operate a first group of compressors in partial load operation of the electrolyzer, while the compressor or compressors of a second group are individually switched on or off in full load operation.

[0013] The advantages and preferred embodiments listed below with regard to the process can be transferred analogously to the electrolysis plant.

[0014] The invention is based on the idea of ​​adapting the design and control of the compressors to the load variations of the electrolysis process in a cost-effective manner. This is done by designing not all compressors for part-load operation, but rather only some of the compressors, which form the first group. The remaining compressors are operated during part-load operation of the electrolysis plant, either at full load or switched off: these form the second group. Each group can comprise one or more compressors. If the plant only contains two compressors, one is assigned to the first group and the other to the second group.

[0015] The process described above has the advantage that the connected compressors of the second group can operate at their optimum. Each compressor in the second group is controlled individually, i.e. independently of the other compressors in the second group. This ensures a high level of flexibility when adapting the compression capacity to the partial load operation of the electrolysis plant. If there are a large number of compressors, these are arranged in parallel compressor trains. Individual compressor trains are switched on and off in a way that optimises efficiency. This applies to all compressors, but is particularly relevant for the compressors in the second group. Load changes are only achieved by a subset of the compressor trains.

[0016] In parallel, the electrolyzer is operated with optimized efficiency to achieve maximum overall system efficiency. The operator or control unit has the option of preselecting the partial load of the electrolysis system according to the compressor operating points with optimal efficiency. This results in a relatively fine-tuned adjustment of the efficiency-optimized system operating points. Load changes are carried out, as already described, with the compressors of the first group equipped for partial load operation and by switching the compressors of the second group on or off. The change between the different load points can be implemented abruptly or continuously, with continuous change being the preferred variant.

[0017] Furthermore, it is advisable to adapt the electrolyzers and their process units to the compression process according to their dimensions and bundling, especially so that they achieve optimum efficiency at the efficiency-optimized compressor operating points. This can improve the overall efficiency of the electrolysis plant, as the compressors can also operate closer to or at the efficiency-optimized operating points.

[0018] According to a preferred embodiment, part-load operation is set for the first group of compressors using a frequency-controlled drive. These compressors can smooth out the possible compressor operating points or adapt to the electrolysis behavior at part load. Compared to alternative designs for achieving part-load operation, such as valve shutdown (reducing mass flow by switching the valves on / off) or changing the compressor volume, the use of a frequency-controlled drive is characterized by the best efficiency, i.e., the lowest energy consumption.

[0019] According to a further preferred embodiment, the compressors are operated in parallel. This allows particularly high product mass flows to be compressed. The compressor trains are formed by the parallel connection, with each train comprising one or more compressors.

[0020] For a particularly cost-effective design, the number of compressors in the first group is preferably lower than the number of compressors in the second group. Only a minimal portion of the compressors or compressor trains used are equipped for part-load operation, e.g., with frequency-controlled drives. At the same time, as many of the active compressors as possible are operated at maximum efficiency (in full-load operation) to reduce part-load losses.

[0021] Preferably, the first and second groups of compressors are used to compress only the hydrogen produced, since hydrogen is the main product of the electrolysis process, and compression is therefore always advantageous. The compressors are advantageously designed as piston compressors and / or screw compressors, as these types of compressors are best suited to the load range of the mass flow produced in the electrolysis process.

[0022] An exemplary embodiment of the invention is explained in more detail with reference to a drawing. The single figure shows an electrolysis plant 2, comprising an electrolyzer 4 for producing the products hydrogen 6 and oxygen 8. Each of the product streams 6, 8 is subjected to gas conditioning, which is shown by the block 12. Gas conditioning refers to the catalysis of the external gases, in which the residual oxygen in the hydrogen stream is thermally reacted with oxygen, and vice versa on the oxygen side. The respective product gas is then generally dried and, if necessary, cooled. The products can then initially be stored in a gas container 14 or directly compressed by several downstream compressors 10.

[0023] Electrolyzer 4 is, for example, a proton exchange membrane (PEM) electrolyzer or an alkaline electrolyzer. Alternatively, it can be, for example, an anion exchange membrane (AEM) electrolyzer. In the figure, electrolyzer 4 represents several electrolysis units arranged in series or parallel.

[0024] Two or more compressors 10 are provided on each product side ( 10 a , 10 b , ... 10 n , where n>=2 ). These are arranged in parallel in so-called strings. In the figure, only one compressor 10 is shown per compressor string. a , 10 b , - 10 n Alternatively, the lines can also contain two or more compressors. A series connection of the compressors 10 a , 10 b , ... 10 nas well as any combination of parallel and series connections are also conceivable and depend on the requirements of the electrolysis plant 2. Each of the compressors 10 is equipped with a drive 16. At least one compressor 10 a also has a variable frequency drive 18, which comprises a frequency converter. The frequency controlled drive 18 enables infinitely variable speed control by means of a three-phase alternating current induction drive. On the respective product side, the compressor(s) 10 form(s) a with the frequency-controlled drive 18 a first group A. The remaining compressors 10 b ... 10 n form a second group B in the illustrated embodiment.

[0025] The compressed products hydrogen 6 and oxygen 8 are finally conditioned in step 20 and led out of the electrolysis plant 2.

[0026] The electrolysis plant 2 also has a control unit, which is symbolically indicated by the block 22. The control unit 22 controls in particular the drives 16 of the compressors 10 a , 10 b , - 10 n based on data from electrolyser 4 .

[0027] Under certain circumstances, the load of the electrolyzer 4 may be below its full load, i.e., the electrolyzer 4 operates at partial load. In this case, the control unit 22 controls the first group A of compressors 10 such that they are also operated at partial load, while the compressors 10 of the second group B are switched on or off individually, i.e., independently of one another. When the compressors 10 of the second group B are switched on, they operate at full load. During the design of the electrolysis system 2, the optimum efficiency of the system components is coordinated with one another, i.e., the number of compressors 10 is, in particular, adapted to the number of electrolysis units, so that an efficiency-optimized operation of the entire system is possible. The figure shows a distribution of the compressors 10 on each of the two product sides. a , 10 b , ... 10 nshown in two groups A, B. However, it is also conceivable to use one or more compressors 10 for only one product, especially on the hydrogen product side. a to be equipped with a frequency-controlled drive 18.

Claims

Patent claims Method for operating an electrolysis plant (2) comprising at least one electrolyzer (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 electrolyzer (4), wherein in a partial load operation of the electrolyzer (4) a first group (A) of compressors (10 a ) is operated at partial load, while the compressor(s) (10 b , ... 10 n ) of a second group (B) can be individually switched on or off in full load operation. Method according to claim 1, wherein in the first group (A) of compressors (10) the partial load operation is set via a frequency-controlled drive (18). Method according to one of the preceding claims, wherein the compressors (10) are operated in parallel. Method according to one of the preceding claims, wherein the number of compressors (10 a ) of the first group (A) is less than the number of compressors (10 b , ... 10 n ) of the second group (B) . Method according to one of the preceding claims, wherein the first (A) and the second group (B) of compressors (10) are used to compress only the hydrogen (6) produced. Electrolysis plant (2) which is suitable for carrying out the method according to claim 1, comprising at least one electrolyzer (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 electrolyzer (4), so- such as a control unit (22) which is designed to control a first group (A) of compressors (10 a, ) in partial load operation, while the compressor(s) (10 b , ... 10 n ) of a second group (B) individually in full load operation. Electrolysis plant according to claim 6, wherein the compressors (10) are designed as piston compressors and / or screw compressors.

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