Electrolysis plant and plant network comprising an electrolysis plant and a renewable energy plant

Abstract

The invention relates to an electrolysis plant (1) comprising an electrolyser (3) and a circuit assembly (5) having an input (7) for connecting to an external DC source and an output (9) connected to the electrolyser (3). The circuit assembly (5) has a transformer (11) with an inverter (13) connected on the primary side and a rectifier (15) connected on the secondary side, such that a direct current can be supplied to the electrolyser (3). The invention also relates to a plant network (100) comprising a electrolysis plant (1) and a renewable energy plant (50) that is directly connected to the electrolysis plant (1).

Description

[0001] Description

[0002] Electrolysis plant and plant network comprising an electrolysis plant and a renewable energy plant

[0003] The invention relates to an electrolysis system comprising an electrolyzer and a circuit arrangement. The invention further relates to a system combination comprising an electrolysis system and a renewable energy system connected to the electrolysis system.

[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, for example, using 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 a direct current (DC voltage). After passing through the electrolysis cells, two fluid streams consisting of water and gas bubbles (O2 and H2 respectively) emerge.

[0006] Current considerations are to use surplus energy from renewable energy sources during periods of abundant sun and wind, i.e., when solar or wind power generation exceeds average levels, to generate valuable resources. One such resource could be hydrogen, which is produced by water electrolysis plants. Hydrogen can, for example, be used to produce so-called renewable energy gas—also known as EE gas. EE gas is a combustible gas that is obtained from renewable sources using electrical energy.

[0007] Hydrogen represents a particularly environmentally friendly and sustainable energy source. It has the unique potential to realize energy systems, transport, and large parts of the chemical industry without CO2 emissions. For this to succeed, however, the hydrogen cannot come from fossil sources, but must be produced using renewable energy. At least a growing share of the electricity generated from renewable sources is now fed into the public power grid. Thus, depending on the electricity mix, a corresponding share of green hydrogen can be produced if an electrolysis plant is operated with electricity from the public grid.

[0008] In industrial-scale electrolysis, the direct current is predominantly provided by line-commutated rectifiers. This rectification of a line-side alternating voltage can result in harmonics due to the way the rectifiers operate, which can place a strain on the AC and / or DC grids.

[0009] EP 3 723 254 A1 discloses such an electrolysis plant which is connected to the public power grid and is accordingly supplied with mains current. For this purpose, the electrolysis plant has a circuit arrangement which comprises four coil arrangements and four rectifiers. The first coils of the coil arrangements are each connected to the DC voltage side of one of the rectifiers. The circuit arrangement also comprises two transformers, which each have a primary winding and two secondary windings. The primary windings of the transformers are connected to the power grid, e.g. a medium-voltage grid or a high-voltage grid. In this way, despite the reduced iron content within the first coil, a desired smoothing of the direct current and damping of the harmonics can take place. One source of renewable energy arises from the increasing use of wind power.Large electrical outputs can be achieved, particularly with offshore wind turbines. However, the challenge is that they are located far away from the consumers. The energy should therefore be transported to the consumer with as little loss as possible. Hydrogen is a highly suitable transport medium and energy carrier. It can be transported in gaseous form, for example, through pipelines. A positive side effect is that a hydrogen-carrying pipeline can also serve as an energy storage device, since the internal pressure can be varied within certain limits.

[0010] Based on these considerations, it is of particular economic interest to produce hydrogen directly at the energy generation site, i.e., autonomously and independently of the public grid. To this end, it is proposed to install the electrolysis plants on offshore platforms in the maritime sector, directly adjacent to or in the immediate vicinity of offshore wind turbines, and to supply them with electricity using the generated power.

[0011] Similar concepts have also been proposed for the mainland, whereby electricity from onshore wind turbines or photovoltaic systems could be used, at least in part, for hydrogen production by directly connecting and feeding it into an electrolysis plant. In all of these applications, the electrolysis plant is part of an island grid. The electrolysis power is therefore not drawn from the public grid, but rather supplied directly by a wind turbine or a PV system and fed into an electrolyzer in the electrolysis plant. It may also be possible to temporarily store the electrical energy generated by a wind turbine or a PV system, for example, in a battery.In contrast to the grid-controlled operation described above, this brings with it particular challenges and problems with regard to the electrical connection and interconnection of the electrolysis plant with the respective renewable energy generation plant, be it a wind turbine or a photovoltaic plant, in particular to ensure safe and, above all, trouble-free operation of the electrolysis plant in a direct plant network with the renewable energy generation plant.

[0012] The invention is therefore based on the object of specifying an electrolysis plant by means of which electricity from a renewable source can be fed directly and smoothly into the electrolysis plant.

[0013] This object is achieved according to the invention by an electrolysis system comprising an electrolyzer and a circuit arrangement which has an input for connection to an external direct current source and an output which is connected to the electrolyzer, wherein the circuit arrangement has a transformer to which an inverter is connected on the primary side and a rectifier is connected on the secondary side, so that a direct current can be supplied to the electrolyzer.

[0014] The invention is based on the knowledge that electrolysis systems, in particular the PEM water electrolysis cells of the electrolyzer, are very sensitive to high-frequency stray electrical currents. These stray currents can couple into the electrolysis system via earth connections or earth faults. Due to necessary system components of an electrolysis system such as process technology, gas separators, auxiliary systems, water-carrying supply lines, etc., the connection to earth on the electrolysis side is inadequate (earth fault or ground loop). It is therefore important, on the one hand, to prevent current paths from closing via the earth, i.e., forming an earth fault or earth loop. On the other hand, the coupling of electromagnetic interference fields per se should be avoided as far as possible, or at least the interference should be reduced.This problem is particularly pronounced when an electrolysis system is directly connected to a DC power source, such as a photovoltaic system or a wind turbine.

[0015] In this complex system consisting of a renewable energy generation plant and an electrolysis plant with direct feed-in of the electrolysis current from renewable sources to operate the electrolysis, the adverse effects of a ground loop and the coupling of alternating electromagnetic fields into the power electronics components used are scaled accordingly. For example, the widespread and preferred use of insulated-gate bipolar transistors (IGBTs) in the rectifier that supplies the electrolysis with high current. The IGBT is a semiconductor component used in power electronics because it combines the advantages of a bipolar transistor such as good conduction behavior, high blocking voltage, robustness, and the advantages of a field-effect transistor through almost power-free control.For example, in a so-called three-phase B6 bridge circuit with an IGBT-based rectifier, this achieves very precise control of the electrolysis current with good rectification. The distinctive advantages of IGBTs are their high voltage and current limits: voltages of up to 6500 V and currents of up to 3600 A at a power of up to 100 MW, making them ideal for use in electrolysis plants.

[0016] With the invention, an AC intermediate circuit is provided in an electrolysis plant by the circuit arrangement, which provides galvanic decoupling between an external DC source and the electrolyzer. In the AC intermediate circuit, the inverter converts the DC voltage from the external DC source into an AC voltage, which is coupled to the transformer on the primary side. A rectifier is connected on the secondary side of the transformer and converts the voltage back into a DC voltage, specifically at a voltage or current level desired and predetermined for the electrolysis. The circuit arrangement is therefore particularly advantageously designed as an AC intermediate circuit and conceived for the provision of DC current from an external DC source to supply the electrolyzer with electrolysis current. This is achieved by direct coupling or.Direct connection of the input to an external DC power source. A wind turbine or a photovoltaic system can be advantageously connected to the electrolysis system as an external DC power source. These systems can be designed to operate independently of the grid in so-called island mode, advantageous for both offshore and onshore applications.

[0017] The external DC power source can be connected directly via the input of the circuit arrangement, thus providing a DC power supply for the electrolyzer. The galvanic isolation and decoupling via the AC intermediate circuit reliably prevents damaging interference from high-frequency stray currents and thus earth fault currents and unwanted voltage losses in the electrolyzer. At the same time, a simple and reliable direct connection of the electrolysis system to a renewable energy generation system is achievable, enabling grid-independent operation. The AC intermediate circuit advantageously enables particularly good and flexible adaptation to changing voltage or current levels on the power generation side.

[0018] The galvanic isolation provided by the invention is preferable for another reason, particularly in alkaline electrolysis applications based on alkaline electrolysis. Galvanic isolation advantageously reduces the ground and stray currents caused by the electrolysis. The reason for this is that the ground loop cannot be closed. Galvanic isolation also advantageously breaks the current loop through the ground. Preferably, the secondary side of the transformer in the AC intermediate circuit is not grounded.

[0019] This not only provides effective protection against high-frequency signal components on the connecting cable from the power source, but also noticeably reduces and suppresses DC stray currents, as a closed earth loop is then created again.

[0020] The voltage on the input side of the AC intermediate circuit is preferably selected to be higher than required for electrolysis operation. This reduces losses and reduces the required cross-section of copper or aluminum cables, thereby saving costs and allowing longer cable runs—for example, from the tower of a roughly 100-meter-high wind turbine down to the electrolysis plant.

[0021] In a preferred embodiment, the rectifier is controllable and / or designed as a three-phase rectifier, in particular as a B6 bridge rectifier.

[0022] The controllability of the rectifier(s), which are advantageously designed as three-phase rectifiers or as B6 bridge rectifiers, makes it possible to adjust the total current generated by the rectifier(s) and thus, for example, to control the operation of an electrolyzer connected to the circuit arrangement.

[0023] It is preferably provided that the alternating current frequency in the circuit arrangement can be set to a predetermined value. By designing the circuit arrangement as an AC intermediate circuit, this does not have to be connected to a public grid, and there is therefore a great deal of freedom in choosing the alternating current frequency in the transformer. A high-frequency transformer is advantageously provided here, so that deviations from the usual frequencies in public grids are possible. In a preferred embodiment of the electrolysis plant, the circuit arrangement is designed for an alternating current frequency that is higher than the usual grid frequencies of 50 Hz to 60 Hz in public grids. It is advisable to use high frequencies here, as this allows the size and weight of the transformer, as well as the use of materials, to be reduced.This aspect is particularly advantageous when the electrolysis system is directly connected to a wind turbine. Due to its more compact design and lower weight at high operating frequencies, the transformer can be housed, for example, in the nacelle of the wind turbine or in the base of the wind turbine tower. The entire circuit arrangement can also be located there. This allows the electrolysis system to be located in the immediate vicinity of the wind turbine, for example, allowing short cable runs for the connection.

[0024] In a particularly preferred embodiment, the circuit arrangement is designed for an alternating current frequency of 500 Hz to 50 kHz, in particular from 10 kHz to 30 kHz. This frequency relates to the frequency of the inverter and the rectifier, which are connected to the transformer. In order to exploit the space and cost advantages, a high-frequency intermediate-circuit transformer is provided as the transformer.

[0025] Furthermore, the transformer is preferably set to a transformation ratio or a voltage swing of less than 10, in particular between 1.5 and 7.5. This can be flexibly adapted to the requirements of the electrolyzer or the desired voltage level for the electrolysis process.

[0026] The ratio of the number of turns, or the primary and secondary voltages, is also referred to as the transformation ratio. By selecting the appropriate transformation ratio, i.e., the number of turns, the transformer can both step up and step down alternating voltages. This allows for adaptation with regard to electrolysis.

[0027] However, a voltage swing of greater than 10 is also possible, depending on the application and design of the electrolysis plant and specifically the transformer used. Known electrolysis plants typically operate with a maximum of 1500 V DC, which is still a low-voltage range. However, more than 15 kV DC can be provided and available for connection to a power generation plant. Therefore, an upper limit for the voltage swing of up to, preferably, 70 can be selected. The available connection voltage can then be up to around 70 kV - for example if the electrolysis plant were to be operated at just 1000 V DC. Currently available wind turbines, for example, can produce output voltages of 66 kV AC.

[0028] Preferably, the voltage on the power generation plant side is higher than on the electrolysis plant side.

[0029] A further aspect of the invention arises from the design of the electrolysis system for a preferred electrical connection of the electrolysis system to an external direct current source, wherein a renewable energy system is directly electrically connected to the electrolysis system. This creates an integrated system network.

[0030] In a particularly preferred embodiment, the system combination comprises an electrolysis system and a renewable energy system which has an output for providing direct current, so that a direct current source is formed by the renewable energy system, the output being electrically connected to the input of the electrolysis system.

[0031] This makes it possible to operate the plant in an island network independent of the public grid and to use electricity exclusively from renewable sources for electrolysis, so that green hydrogen is produced.

[0032] Preferably, the renewable energy plant in the plant network is a wind turbine. The wind turbine preferably further comprises a rectifier, the output of which is connected to the input of the circuit arrangement or is electrically connected to the input. The rectifier converts the alternating current from the wind turbine into direct current and, at the same time, advantageously provides the desired input direct voltage level for connection to the electrolysis plant. Furthermore, this rectifier is preferably designed for coordinated operation with, or for suitable control of, the connected generator.

[0033] In an alternative embodiment, it is preferably also possible for the renewable energy system in the system network to be a photovoltaic system. A PV system already provides direct current during operation. However, it is preferably provided that the photovoltaic system in the system network has a DC / DC controller or DC / DC converter which is connected to the input on the output side. It is also possible for such a DC / DC converter (DC-DC converter) in a photovoltaic system to already have galvanic isolation provided and integrated. In this case, only one further downstream DC / DC converter is preferably required to set the voltage for the electrolysis systems and bring it to the desired direct current level for the electrolysis.

[0034] A DC-DC converter, also called a DC-DC converter, is an electrical circuit that converts a DC voltage supplied at the input into a DC voltage with a higher, lower or inverted voltage level. The conversion takes place with the help of a periodically operating electronic switch and one or more energy storage devices. DC-DC converters are self-commutated power converters. In the field of electrical power engineering, they are also known as DC / DC controllers. The inductance used to temporarily store the energy (inductive converter) consists of a coil or a converter-transformer. Known converter-transformers advantageously already provide galvanic isolation, so that their use may be preferred under certain connection conditions and technical circumstances.

[0035] Advantages and advantageous embodiments of the electrolysis plant of the invention are to be regarded as advantages and advantageous embodiments of the plant network and vice versa.

[0036] Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the single figures can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0037] Examples of the invention are explained in more detail with reference to the accompanying drawings. These show schematically and in a highly simplified manner:

[0038] FIG 1 shows a plant combination with an electrolysis plant and a wind turbine;

[0039] FIG 2 shows a system combination with an electrolysis plant and a photovoltaic system.

[0040] : The same reference numerals have the same meaning in the figures. FIG 1 shows a system combination 100 according to the invention. The system combination 100 comprises an electrolysis system 1 and a wind turbine 50A connected to the electrolysis system 1 as a renewable energy system (RE system) and source of green electricity. The electrolysis system 1 has an electrolyzer 3 and a circuit arrangement 5 which is electrically connected to the electrolyzer 3. The circuit arrangement 5 is connected to the electrolyzer 3 via the output 9. Furthermore, the circuit arrangement has an input 7 via which a direct current can be supplied to the electrolysis system. The direct current from a direct current source is supplied via the circuit arrangement 5. For this purpose, the circuit arrangement 5 has an inverter 13, a transformer 11 and a rectifier 15.The circuit arrangement 5 thus provides an AC intermediate circuit in the electrolysis system, by means of which the input 7 is galvanically decoupled from the output 9. The inverter 13 is connected to the transformer 11 on the primary side. The rectifier 15 is connected to the transformer 13 on the secondary side. The electrolyzer 3 is supplied with a direct current, the electrolysis current, via the rectifier 15 of the circuit arrangement 5. The electrolyzer 3 can be designed as a PEM electrolyzer, as an AEM electrolyzer (AEM: anion exchange membrane), or as an alkaline electrolyzer.

[0041] To supply direct current for the electrolysis process, the electrolysis system 1 is connected directly to the 50A wind turbine. The connection is made via input 7 of the circuit arrangement 5, which is designed to receive and transmit direct current to the inverter 13.

[0042] The wind turbine 50A initially generates an alternating current in the generator. In order to supply a direct current to the electrolysis system 1, a rectifier 52 is provided, so that the connection is made via this rectifier 52, the rectifier advantageously being an electrical power component of the wind turbine 50A. In order to vary the voltage or current for the electrolysis, the rectifier 15 is adjustable and is designed as a three-phase rectifier in the form of a B6 bridge rectifier. This has an IGBT (not shown in detail) as a semiconductor component, an insulated-gate bipolar transistor. This is a component often used in power electronics because it combines the advantages of a bipolar transistor, such as good conduction behavior, high blocking voltage, robustness, and the advantages of a field-effect transistor, with almost power-free control.The striking advantages of IGBTs are their high voltage and current limits, with operating voltages of up to 6500 V and currents of up to 3600 A at an output of up to 100 MW. This makes the IGBT ideal for use in the rectifier 15 for the operating range of the electrolyzer 3. Depending on the application, the use of an IGCT, i.e. an integrated gate-commutated thyristor, is also conceivable. This has advantages such as reduced circuitry complexity, an increase in the maximum pulse frequencies for control, and better switching times when connected in series. IGCTs are used in high-power power converters. A single module typically switches several kiloamperes at a typical blocking voltage of 4500 V.

[0043] In the circuit arrangement 5, the alternating current frequency of the transformer 11 can be flexibly set to a predetermined value. In the example, the circuit arrangement 5 is designed for an alternating current frequency that is higher than the usual mains frequencies of 50 - 60 Hz of public networks, which is advantageous. Alternating current frequencies from 500 Hz to 50 kHz, in particular from 10 kHz to 30 kHz, can be set, so that the transformer 11 acts as a high-frequency intermediate circuit transformer. In this frequency range, there are considerable space advantages for the transformer 15, so that a much more compact design with less material is possible compared to mains transformers. In this case, a transformation ratio of less than 10, in particular between 1.5 and 7.5, is set for the voltage level on the secondary side in relation to the primary side in the transformer 11.Transformation ratios of greater than 10 and up to 70 are possible. The circuit arrangement 5 implements galvanic decoupling via a DC intermediate circuit. In this case, the transformer 11 is preferably not earthed at the primary-side star point. Earthing of the transformer 11 at the secondary-side star point is also more preferably not provided. This avoids high-frequency electrical stray currents during operation, which can couple in via earth loops and impair the electrolyzer 3 with its very sensitive electrolysis cells, since the ohmic losses due to earth loops can lead to a very disadvantageous voltage drop across the electrolysis cells.

[0044] All other stray currents to earth in the electrolysis area itself, especially the 0 Hz DC stray currents, are also avoided. This particularly reduces corrosion in the so-called process engineering and in the sensitive auxiliary systems of electrolysis plant 1 and increases the service life of the electrolysis modules and electrolysis cells.

[0045] The lower the electrical resistance of the ground connection between the components involved, the lower the potential difference and the interference current. This is conventionally achieved by using low-resistance cables and connectors, or by using a large shield cross-section, low contact resistance, and the advantageous galvanic decoupling described here.

[0046] During operation of the system network 100, green electricity is generated in the 50A wind turbine. The alternating current generated in the generator is converted into direct current in the rectifier 52. As a result, the renewable energy system 50 - using the 50A wind turbine as an example - provides a direct current source, so that a direct current is fed directly into the input 7 of the electrolysis system 1 via an output of the rectifier 52 and initially passed on to the circuit arrangement 5. In the circuit arrangement 5, the circuits are galvanically isolated by the transformer 11, so that stray currents are suppressed or avoided. First, the primary side of the transformer 11 is converted into an alternating voltage. The transformer 11 transforms this alternating voltage on the secondary side to a desired voltage level in accordance with the set transformation ratio.The rectifier 15 provides an interference-free or hum-free electrolysis DC voltage at output 7, which ensures stable operation of the electrolyzer 3, splitting water into hydrogen and oxygen. Ground loops are avoided. The advantageous direct DC connection of the electrolysis system 1 to the 52A wind turbine enables off-grid island operation and decentralized generation of green electricity, onshore or offshore, depending on the application. The proportion of green hydrogen is 100%.

[0047] In a further exemplary embodiment of a system network 100 according to the invention, FIG. 2 shows an alternative direct current source for supplying the electrolysis system 1 with direct current. The renewable energy system 50 has a photovoltaic system 50B with a large number of PV modules (not shown in more detail). The photovoltaic system 50B can, for example, be designed as a large-area and powerful free-field system - preferably in sunny regions - so that PV outputs of 10 MW of electrical power are available for the electrolysis. On the electrolysis system 1 side, a completely analogous system concept to that in FIG. 1 is used and corresponding system components, i.e. with a circuit arrangement 5 and with an electrolyzer 3.

[0048] In order to achieve a desired and advantageous voltage level for connection to the electrolysis system 1, in the example in FIG 2 a DC-DC chopper 54 is connected to the photovoltaic system 50B. A DC-DC chopper 54 is also referred to as a DC-DC converter, so that the DC voltage supplied to its input from the photovoltaic system 50B is converted into a DC voltage with a higher, lower or inverted voltage level. The conversion takes place with the aid of a periodically operating electronic switch and one or more energy storage devices. DC-DC chopper 54, also referred to as DC-DC converters, are among the self-commutated power converters that play a major role in the field of electrical power engineering. The inductance used to temporarily store the energy (inductive converter) consists of a coil or a converter-transformer.By designing it as a converter transformer, galvanic isolation is already achieved.

[0049] The DC / DC converter 54 connected to the photovoltaic system 50B is connected on the output side to the input 7 of the circuit arrangement 5, so that a direct connection to the electrolysis system 1 and supply with PV direct current is achieved, wherein the stray currents are effectively suppressed by the galvanic decoupling.

[0050] The invention provides an electrolysis plant 1 by means of which a direct current from a renewable source can be fed directly and smoothly into the electrolysis plant 1, so that 100% green hydrogen can be generated in the electrolysis. This is particularly advantageous in the described plant network 100 comprising an electrolysis plant 1 and a renewable energy plant 50, which are directly electrically connected to one another.

Claims

Patent claims 1. Electrolysis system (1) comprising an electrolyzer (3) and a circuit arrangement (5) which has an input (7) for connection to an external DC power source and an output (9) which is connected to the electrolyzer (3), wherein the circuit arrangement (5) has a transformer (11) to which an inverter (13) is connected on the primary side and a rectifier (15) is connected on the secondary side, so that a DC current can be supplied to the electrolyzer (3).

2. Electrolysis system (1) according to claim 1, wherein the rectifier (15) is adjustable and / or designed as a three-phase rectifier, in particular as a B6 bridge rectifier.

3. Electrolysis system (1) according to claim 1 or 2, in which the alternating current frequency is adjustable to a predetermined value in the circuit arrangement (5).

4. Electrolysis system (1) according to one of the preceding claims, wherein the circuit arrangement (5) is designed for an alternating current frequency which is greater than the usual mains frequencies of 50 - 60 Hz of public networks.

5. Electrolysis system (1) according to one of the preceding claims, wherein the circuit arrangement (5) is designed for an alternating current frequency of 500 Hz to 50 kHz, in particular from 10 kHz to 30 kHz.

6. Electrolysis system (1) according to one of the preceding claims, wherein the transformer (11) has a turns ratio of less than 10, in particular between 1.5 and 7.

5.

7. Electrolysis system (1) according to one of the preceding claims, wherein the transformer (11) is not grounded at its primary-side neutral point.

8. Electrolysis system (1) according to one of the preceding claims, wherein the transformer (11) is not grounded at its secondary-side neutral point.

9. System (100) comprising an electrolysis system (1) according to one of the preceding claims and a renewable energy system (50) which has an output for providing direct current, such that the renewable energy system (50) forms a direct current source, wherein the output is connected to the input (7) of the electrolysis system (1).

10. Plant system (100) according to claim 9, wherein the renewable energy plant (50) comprises a wind energy plant (50A).

11. System (100) according to claim 10, wherein the wind turbine has a rectifier (52) which is connected to the input (7) on the output side.

12. Plant system (100) according to claim 9, wherein the renewable energy plant (50) comprises a photovoltaic system (50B).

13. System (100) according to claim 12, wherein the photovoltaic system (50B) has a DC converter (54) which is connected on the output side to the input (7).

Images