Electrolysis system, and method for operating an electrolysis system

Abstract

The invention relates to an electrolysis system (100) comprising: a wind turbine (1); an electrolysis plant (5) which is connected to the wind turbine (1) in order to supply electrolysis current, wherein an island network is implemented without connection to a power supply network; and a heat supply device (7) which is coupled to the electrolysis plant (5) and can be operated with a working medium (23), and which has an evaporator (13) and a condenser (11), and which is designed in such a way that, during a standstill mode, condensation heat of the working medium (23) can be transferred to the electrolysis plant (5) by means of the condenser (11) so as to maintain the temperature above a minimum temperature. During a standstill mode, the heat supply device (7) evaporates a working medium and condenses the evaporated working medium (23), condensation heat being generated and transferred to the electrolysis plant (5) so as to maintain the temperature above a minimum temperature and prevent freezing of water-carrying components of the electrolysis plant (5).

Description

[0001] Description

[0002] Electrolysis system and method for operating an electrolysis system

[0003] The invention relates to an electrolysis system and a method for operating an electrolysis system.

[0004] An electrolysis plant is a device that uses electrical current to transform materials (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. Electrolysis plants are connected to power generation plants to supply direct current with electrolysis current, thus forming an electrolysis system. Typically, an electrolysis plant has several electrolyzers, so that with appropriate scaling, high electrolysis capacities for electrochemical material conversion can be achieved.

[0005] Hydrogen is now produced from water using methods such as 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 composed of several electrolysis cells. Water is introduced as the reactant into the electrolysis stack, which is under DC voltage. After passing through the electrolysis cells, two fluid streams emerge, consisting of water and gas bubbles (O2 and H2, respectively).

[0006] Current considerations are to use surplus energy from renewable energy sources during periods of abundant sun and wind, i.e., with above-average solar or wind power generation, to generate valuable materials. One such valuable material could be hydrogen, which is produced by water electrolysis plants. Hydrogen can, for example, be used to produce so-called renewable energy gas. A renewable energy 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.

[0008] One source for generating renewable energy is wind power. Large electrical outputs can be achieved, particularly with offshore wind turbines located close to the coast. The challenge, however, is that the distance to the consumers is great. The energy should therefore be transported to the consumer with as little loss as possible. Hydrogen is an ideal transport medium. 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. For this reason, it is of particular interest to produce the hydrogen directly at the site of energy generation, i.e. to position offshore electrolysis plants directly at offshore wind turbines or in their immediate vicinity.For example, electrolysis systems are currently being discussed at offshore locations, where an electrolysis plant is installed directly on the platform of an offshore wind turbine. The wind turbine can be interconnected with the electrolysis plant to form a largely self-sufficient, i.e., virtually grid-independent, electrolysis system, and can be specially equipped for offshore island operation. However, island grids without a grid connection for the electrolysis plant are also possible onshore in remote areas.

[0009] In the best case scenario, these electrolysis systems, comprising a combination of a wind turbine and an electrolysis plant, can be built entirely without any auxiliary connection to a power grid and can be designed exclusively for island operation, both in an onshore and offshore installation. Electrolysis systems built far off the coast are particularly challenging, as long connection routes to the public grid in the coastal region can be avoided or are not economically viable. The electrolysis plant with a number of electrolyzers is ideally located in the immediate vicinity of the renewable energy sources, i.e. the wind turbine, in order to reduce or avoid both transformation and transmission losses.For this reason, offshore electrolysis systems are currently being intensively developed, with electrolysis units installed directly on a platform with an offshore wind turbine. With such a coupling, whether onshore or offshore, the system can be operated without a connection to the power grid. Without a grid connection, however, during periods of calm, lulls, or planned maintenance, for example, at the wind turbine's turbine, no power is available from the generator or the power grid.

[0010] In offshore electrolysis systems, special attention must be paid to preventing corrosion of the electrolysis plant, as the presence of salt water can lead to significantly higher corrosion rates, jeopardizing the long-term uninterrupted operation of an electrolysis plant. In principle, offshore electrolysis plants can be equipped with electrolyzers and housed within closed enclosures, called containers. This provides a certain degree of protection for the electrolyzer from external environmental influences. However, for operational reasons, the electrolyzer must be cooled during normal operation in order to continuously dissipate the waste heat generated from the electrolysis process to the environment.In general, compared to onshore electrolysis plants, heat management in offshore electrolysis plants is particularly challenging, both with regard to the necessary cooling during normal operation and with maintaining a minimum temperature during extended downtimes. In the latter case, sufficient freeze protection for the water-soaked electrolysis cells of the electrolyzers must be ensured, especially during periods of calm weather and when the wind turbine is shut down in the winter months. With regard to the cooling requirements during normal operation of offshore electrolysis plants, at least a closed container design, i.e. an enclosure to protect the electrolyzer, is therefore established. This requires, on the one hand, to avoid overheating and failure of the electrolyzers and, on the other hand, damaging corrosion caused by exposure to maritime salt.Thus, in an offshore electrolysis plant, an interface and exchange between the electrolyzer and the environment is ultimately unavoidable in order to appropriately dissipate the heat flow of the process heat during normal operation and to enable safe operation.

[0011] To protect the electrolyzers from environmental influences, they therefore require an enclosure such as a container, as explained above. PEM water electrolyzers must also be operated with demineralized, and in particular ultra-pure, water. The temperature inside the container must therefore not fall below approximately 5°C. Otherwise, the water-bearing components, which contain water, can freeze and bring the entire system to a standstill. This would defeat the purpose of low-maintenance and self-sufficient operation of offshore electrolysis systems with wind turbines without grid connection. If the temperature outside the enclosure is below 5°C, heat is transported from the interior of the container to the outside by conduction, convection and radiation.At the minimum design temperature outside of -20 °C, around 1 to 2 kW of heat energy per hour is dissipated from each container in the electrolysis plant. The heat loss depends, among other things, on the insulation of the container itself. This heat must be fed back into the container in order to keep the 5 °C reasonably constant and to reliably prevent damage from freezing. This temperature maintenance in the container can be guaranteed during normal operation of the electrolysis plant, i.e. when supplied with electrolysis power from the wind turbine, even at very low ambient temperatures, because sufficient waste heat is available from the electrolysis process.

[0012] If, on the other hand, renewable electricity is not available during very cold weather - for example because there is no wind or if the wind turbine has to be shut down for unforeseen maintenance - the heat energy to maintain the temperature in the electrolysis plant must be provided safely and reliably by another source. Otherwise, there is a risk of irreversible damage to the electrolysis cells due to frost and even total loss of the electrolyzers installed in the electrolysis plant. The water pipes between the containers or enclosures must also be kept at a minimum temperature to prevent them from freezing. This also requires energy, which has to be provided from other sources when there is no wind.

[0013] Solutions that have already been proposed include the use of and recourse to appropriately designed battery storage in the electrolysis system. The battery storage provides electrical power to maintain electrical heating and temperature. However, this solution has considerable disadvantages. For example, the capacity of battery units and the installation space on an offshore platform are significantly limited. Realistically, for the present application on an offshore wind turbine platform, for example, quite high battery capacities of at least 100 to 150 kWh would be required to ensure temperature maintenance even during extended periods of standstill.

[0014] This appears uneconomical with currently available battery technologies. Especially in cold ambient temperatures, the cold slows down batteries. This is because the electrolyte becomes more viscous and harder to penetrate. As a result, fewer ions reach the positive pole, and battery performance drops dramatically. The cold significantly slows down processes in the battery, and the battery wears out faster than usual. So-called battery energy storage systems (BESS) also have the disadvantage of being quite expensive, large, and heavy. Therefore, there is an urgent need for other, better solutions for maintaining temperature during standstill operation of an offshore electrolysis system.

[0015] Another, technically simple solution is the integration of a diesel generator for emergency power supply and operation of a heating system on the offshore platform. However, this solution has the disadvantage that the diesel fuel must be regularly refilled, thus the basic idea and objective of developing reliable, CO2-free offshore electrolysis systems cannot be realized with this approach.

[0016] The object of the present invention is therefore to provide an electrolysis system that enables safe and environmentally friendly operation, while simultaneously designing it for operation that is as self-sufficient and low-maintenance as possible. A further object is to provide a method for operating an electrolysis system.The object directed to an electrolysis system is achieved according to the invention by an electrolysis system comprising a wind turbine and an electrolysis plant which is connected to the wind turbine for supplying electrolysis current, wherein an isolated network is realized without connection to a supply network, further comprising a heat supply device which is coupled to the electrolysis plant and can be operated with a working medium, which has an evaporator and a condenser and which is designed in such a way that in standstill operation, condensation heat of the working medium can be transferred to the electrolysis plant by means of the condenser, so that a temperature is maintained above a minimum temperature.

[0017] The object directed to a method for operating an electrolysis system is achieved according to the invention by a method for operating an electrolysis system, wherein in a standstill operation a working medium is evaporated by means of the heat supply device and evaporated working medium is condensed, wherein condensation heat is generated and transferred to the electrolysis system, so that a temperature is maintained above a minimum temperature and freezing of water-carrying components of the electrolysis system is prevented.

[0018] The advantages and preferred embodiments listed below with regard to the electrolysis system can be transferred analogously to the method for operating the electrolysis system.

[0019] The invention is based on the recognition that the increasingly installed, more powerful, grid-independent wind turbines, particularly offshore wind turbines, and their growing electrical generation capacity require correspondingly more powerful electrolysis systems. It is therefore expected that the power class of electrolysis systems and their number will increase significantly in the future. This particularly applies to offshore electrolysis systems.

[0020] The associated increasing demands on safe and environmentally friendly operation in a maritime environment must be taken into account. Due to the scaling efforts towards larger offshore electrolysis systems far off the coast, the question of the most self-sufficient, i.e. grid-independent, island operation with 100% hydrogen production from renewable wind power, as well as the environmental compatibility of such systems, is becoming the focus of discussion. On the one hand, from an environmental point of view, operation with the least possible intervention must be guaranteed. A self-sufficient solution for safely maintaining the temperature of the electrolysis plant with regard to the water-bearing components, in particular the particularly sensitive water-soaked electrolysis cells of a PEM electrolysis plant, in situations with a standstill, especially in the event of a failure of the wind turbine and no electrolysis power, is therefore of crucial importance.The concept of the invention ensures heat supply and temperature maintenance so that there is no risk of failure or loss of water-bearing components even when there is a risk of frost during a period of darkness with low ambient temperatures in the winter months. The invention therefore implements a heat maintenance concept in an electrolysis system, in particular an offshore electrolysis system, which is characterized by high reliability and intrinsic fail-safe operation in critical weather conditions and operating situations. This creates a practically maintenance-free electrolysis system in which the risk of frost damage caused by freezing of water-bearing components of the electrolysis system, in particular the electrolyzer and the electrolysis cells, is reliably countered.This results in a long service life and immediate availability and readiness for resuming normal operation after a shutdown. The electrolysis system of the invention advantageously recognizes and overcomes, for the first time, the disadvantages of conventional heat supply concepts for off-grid electrolysis systems, which—as described above—rely on very large battery units or even diesel generators, which, for example, are installed on the platform in an offshore installation to supply heat to the electrolysis plant. These approaches also prove to be very disadvantageous from an environmental perspective, as well as expensive and maintenance-intensive.

[0021] With the evaporation-based heat supply system, on the other hand, continuous temperature maintenance is ensured even over several days in the dark, with the heat transfer being adjustable with regard to a required minimum temperature, which is maintained. The evaporation enthalpy of a working fluid is advantageously used to provide the necessary heat. The required operating point of the heat supply system can be specifically set via the vapor pressure curve of the working fluid using the pressure and temperature of the working fluid. The working fluid previously evaporated in the evaporator is condensed in the condenser, with condensation heat being released at a constant evaporation temperature. For this purpose, the condenser is thermally coupled to a heat sink so that heat can be dissipated and transferred to the electrolysis system.The evaporator, on the other hand, is thermally coupled to a heat source, causing the working fluid to evaporate. The heat supply system, which is based on condensation heat, can be specifically adapted to the needs of the electrolysis plant with minimal heat output and minimal heat consumption to maintain the temperature. A thermodynamic cycle is advantageously implemented here, so that the working fluid is practically not used up. Furthermore, only small temperature differences are required to carry out the evaporation and condensation process at a working temperature and working pressure of the working medium. The heat supply system is designed in such a way that an isochoric cycle can be carried out with the evaporator and the condenser.

[0022] In a particularly preferred embodiment of the electrolysis system, the heat supply device comprises a gravity-driven heat pipe, wherein the condenser is formed above the evaporator on the heat pipe.

[0023] This advantageously provides a heat supply system based on a self-circulating working fluid. Due to the vertical arrangement and orientation of the heat pipe, the evaporator is positioned vertically at the bottom and the condenser vertically at the top. Thus, evaporation heat from a low-lying heat source coupled to the evaporator can be transported vertically upwards to the condenser via the evaporated working fluid, whereby an independent gravity-driven cycle is implemented in the heat pipe.

[0024] This involves using a heat pipe which is advantageously integrated into the heat supply system. Heat pipes are components which can transfer heat via an evaporation and condensation circuit. If heat is supplied to one end of the heat pipe, the working fluid evaporates and, driven by the temperature or pressure gradient, flows along the adiabatic zone to the condenser. There the vapor condenses and releases its latent heat to an external heat sink. To maintain the circuit, the condensate must be fed back to the evaporator. For this purpose an integrated wick structure (e.g. grooved, mesh or sintered structure) is usually used which transports the condensate back to the evaporator using capillary force. If the condenser is located above the evaporator, gravity can also be used for the return transport, as is preferred here.This type of heat pipe is also known as a two-phase thermosiphon. The use of other forces, such as centrifugal forces, is also conceivable for the return of the working fluid. The working fluid used depends on the temperature range in which the heat pipe is to be used. In general, large working ranges are available depending on the vapor pressure curve. Advantageous applications are in the range from approximately -100 to 300 °C. Here, for example, working fluids such as carbon dioxide, ethanol, acetone, water or other working fluids with a vapor pressure curve in the range of the required minimum temperature can be used.

[0025] There are two advantageous designs of heat pipes that can be distinguished: the heat pipe and the two-phase thermosiphon. The basic operating principle is the same for both designs; the difference lies in the return transport of the gaseous working medium to the evaporator, i.e. to the point where heat is added. In both designs, the return transport is passive and therefore without aids such as a circulation pump. The thermal resistance of a heat pipe is significantly lower at working temperature than that of metals. The behavior of the heat pipes is therefore very close to the isothermal change of state. There is an almost constant temperature along the length of the heat pipe.

[0026] In a particularly preferred embodiment of the electrolysis system, the heat supply device has a deep probe which is designed to extract heat from a deep heat reservoir, wherein the evaporator is immersed in the heat reservoir.

[0027] The heat pipe is therefore advantageously designed as a deep probe so that heat of evaporation can be extracted or tapped from a deep heat reservoir as a heat source. The term “immersion in the heat reservoir” is not restrictive in this case but is to be understood functionally. This therefore includes thermal couplings in which the evaporator of the heat pipe is directly or indirectly thermally coupled to the heat reservoir. Partial or complete immersion of the evaporator of the deep probe is also possible. Depending on the installation and anchoring of the electrolysis system, in particular a wind turbine, the heat reservoir can be formed, for example, by deep layers of earth or rock, aquifers, groundwater or thermal water reservoirs, seawater or the seabed.

[0028] In a particularly preferred embodiment of the electrolysis system, the heat supply device has a heat reservoir which is formed within the tower of the wind turbine.

[0029] This advantageously provides an integrated solution for temperature maintenance in the electrolysis system. The heat supply device itself is equipped with a heat reservoir or has a heat reservoir. By integrating the heat reservoir within the tower of the wind turbine, a heat pipe designed as a deep probe is particularly efficient. This heat pipe is arranged and aligned vertically within the tower and projects into the heat reservoir, whereby the heat pipe is also well protected from harmful environmental influences. However, it is in principle also conceivable for the heat supply device to be arranged externally on the tower of the wind turbine, with the heat pipe designed as a deep probe being immersed in the seawater to a depth with a suitable water temperature, e.g. in the case of an offshore installation, as a heat source for the condenser.However, by integrating it into the tower, it is very advantageous to have a heat source deep inside the wind turbine tower and, at the same time, a heat sink is provided in the upper area of ​​the tower for the operation of the heat pipe. Accordingly, the evaporator and condenser of the vertically installed heat pipe are positioned at the heat source and the heat sink, respectively, and are thus thermally coupled. In a preferred embodiment of the electrolysis system, the heat supply device comprises a heat pipe in which the evaporator is connected to the condenser via an adiabatic zone, thus ensuring independent circulation of the working medium in the heat pipe.

[0030] The heat pipe is designed in such a way that it has a sufficiently long adiabatic zone in its vertical extension, at the end of which the evaporator and condenser are arranged. If heat is supplied to the evaporator of the heat pipe, the working fluid evaporates and flows - driven by the temperature or pressure gradient - along the adiabatic zone vertically upwards to the condenser. There the steam condenses and releases its latent heat to an external heat sink, i.e. in standstill operation to maintain the temperature to the connected water-carrying systems of the electrolysis plant. Because of the independent circulation, additional circulation pumps are not required to maintain circulation, so that the gravity-driven heat pipe provides a self-sufficient heat supply system.Small circulation pumps can also be provided by the electrolysis plant for circulating the process water in the water-bearing systems as needed and connecting it to the condenser. However, their operation only requires a small auxiliary battery, which is significantly more cost-effective than providing electrical heat energy to maintain the temperature. Furthermore, longer periods of downtime can be safely bridged.

[0031] In a particularly preferred embodiment of the electrolysis system, a working medium is introduced into the heat pipe under a predetermined working pressure, so that an evaporation temperature in the range from 2 ° C to 10 ° C, in particular between 4 ° C and 8 ° C, is set under the working pressure.

[0032] To maintain the temperature and the associated heat transfer of the condensation heat of the working medium to the electrolysis plant, a preferred operating range is one in which, based on the vapor pressure curve, evaporation or condensation of the working medium is set close to or above the minimum temperature, for example a few degrees above 5 °C evaporation temperature at the vapor pressure. To maintain the temperature of the electrolysis plant and in particular its water-carrying pipes and systems during standstill operation, pressure ranges can be determined by selecting the specific working medium under which the working medium evaporates in the preferred temperature range for temperature maintenance. For operation at the evaporation or condensation point of the vapor pressure curve, only small temperature differences between the evaporator and the condenser are required for the operation of the heat pipe.The heat pipe is filled with the working fluid in a pressure- and gas-tight manner at a predetermined filling pressure as the working pressure. This working pressure is selected so that, under operating conditions in the electrolysis system, evaporation of the working fluid is induced almost above the freezing temperature of water. The pressure-tight closure of the heat pipe ensures an isochoric cycle of evaporation and condensation during operation of the heat pipe.

[0033] In a particularly preferred embodiment of the electrolysis system, the heat pipe is designed as a CCp deep probe, with carbon dioxide CO2 as the working medium.

[0034] The carbon dioxide is introduced for circulating application in the heat pipe designed as a CCp deep probe under an appropriate working pressure close to the evaporation pressure of carbon dioxide for the desired working temperature. In a CCp deep probe, carbon dioxide CO2 is used as the working medium and heat transfer medium for the cyclic process. The CCp deep probe is particularly advantageously designed for operation according to the heat pipe principle. The probe tube contains both liquid and vaporous carbon dioxide CO2. The liquid carbon dioxide CO2 is in the lower area of ​​the probe, the vaporous carbon dioxide in the upper area. As soon as the process is started, similar to a heat pump, the vaporous CO2 is cooled in a condenser in a heat exchanger, i.e. heat is removed, causing the vaporous CO2 to condense. The now liquid CO2 flows downwards in the probe tube.The liquid CO2 absorbs heat from a heat reservoir via the evaporator, e.g. geothermal energy, and thus becomes vaporous and rises again. This creates a continuous cycle. Due to the fact that the CCp deep probe is self-circulating, regeneration of the probe begins immediately when the heat pump function is switched off or interrupted. This equalizes the temperature from the lower (warmer) layers to the higher (colder) layers. In just about 30 minutes, the original temperature is restored, as it was before the system was last switched on. This means that as long as there is a temperature difference in the probe and the lower layers are warmer than the upper layers, the CO2 circulates independently and the probe is regenerated in the upper area.The CO2 evaporates at the bottom due to the warmer temperatures, rises and releases the heat in the colder area, where it condenses and flows back down.

[0035] In a particularly preferred embodiment of the electrolysis system, the carbon dioxide is introduced into the heat pipe under a working pressure of 35 bar to 45 bar, in particular between 37 bar and 42 bar.

[0036] In this way, the heat pipe is upgraded for use in the electrolysis system according to the vapor pressure curve of carbon dioxide (CO2), and an appropriate filling pressure is set. This design results in evaporation temperatures close to the freezing point of water, at approximately 0.5°C to 10°C, in particular approximately 2.5°C to 7.5°C. The heat supply system is thus designed for normal standstill operation, and a desired evaporation temperature can be specifically set for the application using the filling pressure at a reference temperature.

[0037] In a further preferred embodiment of the electrolysis system, an internal heat control is provided for the heat transport, with a valve or a throttle as a control element, so that the forward and return flow of the working medium can be controlled.

[0038] In this way, the temperature maintenance and the achievable minimum temperature of the electrolysis system can be controlled within certain limits via the transferred heat flow. The internal heat transport in the heat pipe itself can be controlled using a valve or a throttle inside the heat pipe as a control element. A throttle that is rotatably mounted and controlled externally by a small motor can vary both the forward and return flow of the heat-transporting medium from the heat source to the heat sink. Alternatively, a small solenoid valve located inside the heat pipe, implemented as a magnetic ball with a return spring, allows the heat flow through the heat pipe to be largely stopped or released again. The throttle has the major advantage over the valve that the thermal conductivity can be continuously controlled as a function of the setting angle.The valve, on the other hand, only allows the heat pipe to be switched on or off, as it can only be opened or closed due to its electromagnet control. The disadvantage of a throttle valve, however, is its outward-facing control shaft, which makes hermetic sealing difficult to achieve. This can lead to undesirably short maintenance intervals.

[0039] In an alternative embodiment, external heat control can therefore also be implemented. This involves two parallel heat pipes, one originating at the heat source and one at the heat sink, which run parallel to each other at a short distance from each other at their ends without touching each other. In this area they are surrounded by a body, a so-called, made of a good heat-conducting material, e.g. copper or aluminum, with two holes that fit the heat pipes as precisely as possible. The thermal conductivity of the entire system can be easily adjusted by pushing the coupler in or out, since the contact area between the heat pipe and the coupler depends linearly on the insertion depth.The coupling with external control by a small battery-operated actuator can, if necessary, be relocated to an easily accessible location, provided that the very low additional thermal resistance of the longer heat pipes allows this detour.

[0040] By means of either internal or external control, temperature can be maintained safely and in a controlled manner even over longer periods of standstill, and efficient heat management is advantageously possible.

[0041] In a particularly advantageous embodiment of the electrolysis system, the evaporator is arranged within the foundation of the wind turbine, so that evaporation of liquid working medium is effected in the evaporator by deep heat.

[0042] This arrangement and thermal coupling of the evaporator creates or brings about a practically unlimited heat reservoir through the foundation, which can, for example, optionally be formed or incorporated as a corresponding heat storage device through a cavity within the tower of the wind turbine itself. The heat reservoir is therefore preferably embedded deep below the water surface within the tower in order to take advantage of the most constant ambient temperature possible deep underground or under water. With this construction, the enclosure in the tower advantageously creates a certain thermal insulation effect and inertia similar to that of a large heat storage device, whereby a largely constant operating temperature is achieved and a heat source is provided.At the same time, the design of a heat storage unit in a cavity deep inside the tower barely impacts the mechanical stability of the tower structure and the nacelle with the wind turbine. Furthermore, space is created or utilized for a heat storage unit that would otherwise remain unused. The heat storage unit requires no space or installation space on the platform itself. The latter can be used without restriction by the heat supply system for the electrolysis plant and its components.

[0043] A particular advantage is that this simultaneously creates an efficient thermal bridge and coupling to the ambient temperature via the foundation, so that a heat source can be provided and used directly in or on the foundation. This ensures a continuous heat input into the heat reservoir at a working temperature, particularly as soon as the heat pipe is activated and the liquid working medium is evaporated by deep heat in the deep evaporator within the foundation of the wind turbine.

[0044] In a further particularly preferred embodiment of the electrolysis system, the electrolysis plant has an electrolyzer arranged in a container and a heat exchanger which, in normal operation, is designed to dissipate process heat from the electrolysis from the container.

[0045] This advantageously ensures that waste heat generated from the electrolysis process during normal operation can be used to maintain the temperature during standstill operation if required and is not simply released into the environment. Normally, during electrolysis operation, the process heat is discharged to the environment from the container surrounding the electrolyzer, which protects it from the weather and salt ingress. In this case, the heat exchanger is advantageously designed to transfer the process heat from the electrolysis to an additional heat storage unit in the heat supply system when required, in particular to store the heat and keep it available for later use to maintain the temperature in addition to the heat pipe based on the use of condensation heat. The process heat is therefore not released to the environment, or at most only partially. This creates redundancy in the heat supply system.

[0046] At the same time, the heat exchanger supports the cooling of the container and thus of the electrolyzer with its large number of electrolysis cells during normal operation. For this purpose, the heat exchanger can, for example, be connected on the primary side to a coolant circuit of the electrolyzer driven by a coolant pump and thermally coupled to it accordingly, so that targeted heat absorption and release as well as further use in the heat supply system on the secondary side of the heat exchanger is achieved. This advantageously enables safe and environmentally friendly operation of an offshore electrolysis system in a closed container design with an electrolyzer arranged in the container, for example a PEM electrolyzer for hydrogen production, and with a coolant pump arranged in the container or a coolant pump tightly flanged to the container.In the latter case, a housing unit is formed between the container and the flanged-on coolant pump, so that, in the sense understood, the coolant pump is also located in the container. With the closed cooling circuit, the heat absorption of process heat from the electrolysis at the plant is achieved via the heat exchanger in the container. It is also possible to provide multiple heat exchangers, with a specially configured heat exchanger forming part of the heat supply system.

[0047] Preferably, a heat exchanger is provided in the electrolysis system which is thermally coupled to the condenser in such a way that, when the system is at a standstill, condensation heat of the working medium can be transferred to water-bearing components of the electrolysis plant. This can be a heat exchanger that is specifically thermally coupled to the condenser. However, it is also possible to implement the thermal circuit in such a way that the same heat exchanger is used which is also used for cooling purposes during normal operation, for example in a container design, in order to conduct the process heat from an electrolyzer arranged in a container. Heat exchangers are therefore used to couple or transfer the condensation heat released via the condenser of the heat pipe to water-bearing components of the electrolysis plant that are at risk of frost. These heat exchangers can also be used during normal operation, i.e.Bidirectionally, also for cooling purposes of the electrolysis system by selectively dissipating the process heat into the environment or, optionally, to a heat storage unit. This allows for dual use in different operating conditions, eliminating the need for an additional heat exchanger, which has a positive effect on the production and operating costs of the electrolysis system.

[0048] In a particularly preferred embodiment of the electrolysis system, one wind turbine has a tower and a platform attached to the tower, with an electrolysis system being arranged on the platform.

[0049] This makes the electrolysis system specially equipped for offshore use, providing a self-sufficient offshore electrolysis system for maritime operation. The electrolysis plant comprises a number of containers located on the platform, which contain electrolyzers, as well as control and auxiliary systems for the electrolysis plant's operation and its electrical connection, as well as its supply from the wind turbine.

[0050] In the case of an offshore application of the electrolysis system, the evaporator is preferably located underwater in deep water layers or on the seabed. The evaporator of the heat pipe can therefore be heated directly or indirectly via the seawater or the seabed, which act as a practically unlimited heat reservoir and heat source. Temperature conditions at deep levels are largely constant, so that the heat pipe can be designed and adjusted to a predetermined operating point with regard to the evaporation temperature. In this case, the design of the heat pipe as a CCp deep probe is particularly advantageous. The CCp deep probe can be accommodated within the tower of the offshore wind turbine, with the evaporator located deep below, for example in the foundation of the tower, and the condenser at platform level for the purpose of favorable thermal coupling to the electrolysis system.

[0051] A further aspect of the invention relates to a method for operating a corresponding electrolysis system. In this method, a working medium is evaporated during standstill operation by means of the heat supply device, and the evaporated working medium is condensed, releasing condensation heat and transferring it to the electrolysis system, thus maintaining a temperature above a minimum temperature and preventing freezing of water-bearing components of the electrolysis system.

[0052] The advantageous use of the vaporization enthalpy of the working medium allows the process to be carried out autonomously and with a high degree of reliability, i.e., without a grid connection of the electrolysis system. The process is therefore advantageous for use in both offshore and onshore electrolysis systems in an isolated operation configuration. The electrolysis system is very advantageously designed for isolated operation, as it ensures temperature maintenance in winter or when there is a risk of frost, particularly during periods of darkness, and prevents freezing through the provision and use of condensation heat.Preferably, in the process, temperature maintenance is initiated at an outside temperature of less than 5 ° C, wherein the working medium is circulated in a gravity-driven heat pipe and condensation heat is extracted from the working medium and transferred to the water-bearing components of the electrolysis plant, so that freezing protection is achieved.

[0053] Preferably, in the method, the heat flow is controlled by a control device, wherein the forward and return flow of the circulating working medium is adjusted, wherein the condensation heat transferred to the electrolysis plant is adjusted.

[0054] Further preferably, in the process, in normal operation, the electrolysis plant is supplied with electrolysis current from the wind turbine, with process heat being discharged from the electrolyzer via a heat exchanger.

[0055] Embodiments, features, and / or advantages that relate to the electrolysis system in this case also apply analogously to the operating method, and vice versa. Examples of embodiments of the invention are explained in more detail below with reference to a drawing. These show schematically and in a highly simplified manner:

[0056] FIG 1 an electrolysis system with an electrolysis plant and with a wind turbine;

[0057] FIG 2 is a schematic side view of the electrolysis system with a heat supply device with a heat pipe;

[0058] FIG 3 a schematic representation of a heat pipe and its operation

[0059] The same reference numerals have the same meaning in the figures. FIG. 1 shows an electrolysis system 100 which is designed for operation on the high seas, i.e. offshore. The electrolysis system 100 comprises an electrolysis plant 5 and a wind turbine 1 which has a tower 19, as shown in the upper right-hand part of FIG. 1. In the lower region of the tower 19, a platform 3 is attached to the tower 19 above sea level 25 (see FIG. 2), which platform is specially designed and configured to accommodate various system components for the intended operation of the electrolysis system 100 in an offshore application. These system components are shown as examples in an enlarged representation in the lower part of FIG. 1:

[0060] An electrolysis plant 5 is set up on platform 3 and is systemically connected to the wind turbine 1 to form the electrolysis system 100. For this purpose, containers 9 are set up on platform 3, in which electrolysis elements (not shown in detail) such as individual electrolyzers are housed, so that particularly sensitive functional components of the electrolysis plant 5 are protected from the effects of the weather, particularly during offshore use. Some of the containers 9 set up on platform 3 comprise control devices 27 or so-called "balance of plant" elements and accommodate them protectively. These are selected containers 9 that are usually reserved specifically for the accommodation and operation of these control devices 27 and, if applicable, other auxiliary systems of the electrolysis plant 5.In contrast, the electrolyzers for electrochemical material conversion are arranged in specially designed containers 9. Other components or system parts housed in the containers 9 may also include storage tanks for the reactant water of the electrolyzers, or the like.

[0061] The wind turbine 1 preferably has no grid connection or grid coupling in the present case, but instead supplies the described electrolysis system 5 with the absorbed wind energy in the self-sufficient electrolysis system 100, which is designed to produce preferably green hydrogen from water electrolysis. The electrolysis system 100 is therefore designed for grid-independent island operation and equipped for self-sufficient use in regions farther from the coast. The wind turbine 1 is therefore an offshore wind turbine. Deviating from the illustrations in FIGS. 1 and 2, the means presented according to the invention for improved heat supply to the offshore electrolysis system 100 can also be readily applied to onshore systems.

[0062] The strategy of providing the electrolysis plant 5 via a number of containers 9, preferably ISO containers, advantageously ensures a simple maintenance and repair process, and simultaneously protects the plant components from climatic and weather influences as well as from corrosion and damaging mechanical influences during operation. The electrolysis system 100 is particularly vulnerable in situations in which the wind turbine 1 does not produce any power for the electrolysis in frost conditions, so that there is an acute risk of water-bearing systems of the electrolysis plant 5 freezing, particularly during a prolonged period of darkness with the associated risk of frost during standstill operation.

[0063] This is counteracted by the invention with a heat supply device 7, as is advantageously integrated into the electrolysis system 100 (see FIG. 2). The heat supply device 7 is coupled to the electrolysis plant 5 and designed such that, in standstill operation, condensation heat can be transferred to the electrolysis plant 5 by means of the heat supply device 7, so that the temperature of the water-conducting systems is maintained above a minimum temperature. FIG. 2 shows, by way of example, a schematic side view of a suitably equipped electrolysis system 100 with a heat supply device 7. The heat supply device 7 is integrated into the tower 19 of the wind turbine 1, fastened at approximately the height of the platform 3 and projects deep within the tower 19 into the underwater region 31 below sea level 25.The platform 3 is attached to the tower 19 in an above-water area 31 and forms a support structure for the electrolysis plant 5. The tower 19 is firmly anchored in the seabed 35 by means of a foundation 33. The heat supply device 7 has a heat pipe 17 which extends approximately from the height of the platform 3 vertically within the tower 19 into the depths, said heat pipe comprising a condenser 11 and an evaporator 13. The condenser 11 is formed or attached to the vertically upper end and the evaporator 13 to the vertically lower end of the heat pipe 13. The heat pipe 17 is designed here as a CO2 depth probe 37 with carbon dioxide CO2 as the circulating working medium 23. The heat pipe 17 is pressure-tight filled with carbon dioxide CO2 at a predetermined working pressure of approximately 35 bar to 45 bar, in particular of approximately 37 bar to 42 bar.In this way, low evaporation temperatures of 2 ° C to 10 ° C, in particular of 4 ° C to 8 ° C, are set due to the vapor pressure curve of the working medium 23. Depending on the choice of working medium 23, a different filling pressure can also be set in the heat pipe 17 in order to set the desired evaporation temperature a few degrees above the freezing point of water for the operation of the heat pipe 17. During operation, the CCU deep probe 37 uses sea water or the seabed 35 as an external heat source. The foundation 33 surrounded by the seabed also functions as a heat reservoir 15 within the tower 19 of the wind turbine 1 in the deep sea layers. In this way, the working medium 23 can be evaporated in the evaporator 13 when the system is at a standstill. The required latent heat of evaporation orThe evaporation enthalpy for the evaporation of the working medium 23 is taken from the CCU deep probe 37 from a deep underwater area 31 of the heat reservoir 15 as an external heat source. The evaporated working medium 23 is automatically conveyed upwards, whereby the heat pipe principle in the heat pipe 17 is specifically utilized. The vaporous working medium 23 condenses in the condenser 11. Condensation heat released from the working medium 23, for example from the carbon dioxide CO2, can thus be transferred via the condenser 11 to the electrolysis system 5 as an external heat sink, e.g. via a heat exchanger 43. The CCt deep probe 37 is arranged with the evaporator 13 at a depth at an advantageous temperature level of the seawater, which is above at least approximately 5 °C as the temperature of the external heat source.For efficiency reasons, the heat pipe 17 is operated at the warmer end only slightly above and at the colder end only slightly below the boiling point of the working medium 23. Thus, small temperature differences are sufficient to maintain the temperature of the electrolysis system 5 above a minimum temperature and thus provide freeze protection.

[0064] This creates a particularly advantageous way of reliably protecting the non-grid-connected electrolysis system 100 from frost damage in offshore operation when the outside temperature above water is below 5°C. The electrolysis system 5, in particular the electrolyzer in a container 9 which is at risk from frost, can be supplied with evaporation heat from the working medium 23 very efficiently by means of the heat supply device 7 with the integrated CCp deep probe 37, which uses the deep sea water as a heat reservoir 15. The electrolysis system 5 has an electrolyzer arranged in a container 9, the waste heat of which can be dissipated as process heat from the container 9 during normal operation, if necessary, also via the heat exchanger 43 or a specially provided cooling circuit. The heat exchanger 11 can therefore also be used to cool the electrolysis system 5 during normal operation, if necessary.The heat pipe 17 of the heat supply device 7 can be structurally integrated into the container 9 in the upper part via the evaporator 11 with the heat exchanger 43.

[0065] In order to illustrate the mode of operation of the evaporation-based heat supply device 7, a heat pipe 17 is shown below in a schematic sectional view with reference to FIG 3. The heat pipe 17 is designed as a gravity-driven CCp deep probe 37 with carbon dioxide CO2 as the working medium 23. The heat pipe 17 has a cylindrical or tubular shape with a predominantly longitudinal extension along a vertical axis. The heat pipe 17 has a condenser 11 at its vertical upper end and an evaporator 13 at its vertical lower end. An adiabatic zone 39 is formed in the heat pipe 17 between the evaporator 13 and the condenser 13. Depending on the selected operating point for the evaporation, the heat pipe 17 is filled in a gas-tight manner with carbon dioxide CO2 at a working pressure of 35 bar to 45 bar; in particular, 37 bar to 42 bar can be set.In this way, an appropriate evaporation temperature of approximately 2 ° C to 6 ° C, in particular 4 ° C to 8 ° C, can be set and adapted to the application situation. During operation, the heat pipe 17 is thermally coupled to the evaporator 13 and a heat reservoir 15, so that an external heat source is provided for evaporating the working medium 23, with heating heat H being transferred to the working medium 23 in accordance with the specific enthalpy of evaporation. Accordingly, the heat pipe 17 is thermally coupled to the condenser 11 and an external heat sink, in this case a heat exchanger 43. At the condenser 11, the heating heat H is released again as condensation heat in accordance with the specific enthalpy of evaporation. The condensation heat can be tapped off via the heat exchanger 43 to maintain the temperature of the electrolysis system 5 and transferred to the electrolysis system 5.In this way, the water-carrying systems of the electrolysis plant 5 in particular are reliably protected from freezing during standstill operation. A control device 41 is provided for the heat transport and is designed as an internal heat control 41 for the heating heat H transferred via the working medium 23. The internal heat control 41 can have a controllable valve or a controllable throttle device as a control element, so that the forward and return flow of the working medium 23 can be controlled and thus the heat transport to the condenser 11 can be controlled. In this way, the temperature maintenance and the achievable minimum temperature of the electrolysis plant can be controlled within certain limits via the transferred heat flow. The internal heat transport in the heat pipe 17 itself can thus be controlled, specifically by means of a valve or a throttle within the heat pipe as a control element.

[0066] The ability of a heat pipe 17 to transport thermal energy depends significantly on the specific enthalpy of vaporization (in kJ / mol or kJ / kg) of the working medium and not on the thermal conductivity of the vessel wall of the heat pipe 17 or the working medium 23. For efficiency reasons, the heat pipe 13 is therefore operated at the warm end only just above and at the cold end only just below the boiling point of the working medium 23 under the specified working pressure.

[0067] The heat pipe 13 is generally a metal vessel of elongated shape or a tube which can be used, in this case designed as a CO2 depth probe 37, and which contains a hermetically encapsulated volume. In the exemplary embodiment, the heat pipe 13 is filled with carbon dioxide CO2 as the working medium 23. However, it is also possible for the heat pipe 13 to be filled with another working medium 23, such as water or ammonia, which fills the encapsulated volume to a small extent in a liquid state and to a greater extent in a gaseous state. The part of the vessel which is used for energy absorption is the evaporator 13, and the part of the vessel which is used for energy release is called the condenser 11. The mode of operation is such that the introduction of heat H increases the temperature of the vessel and the working medium 23 until the boiling point of the working medium 23 is reached.From then on, the working medium 23 begins to evaporate and the temperature no longer increases. Instead, the entire supplied heating energy H is converted into the enthalpy of vaporization. This locally increases the pressure in the heat pipe 13 above the liquid level, which leads to a slight pressure gradient within the heat pipe 13. The resulting vaporous working medium 23 begins to distribute itself throughout the entire available volume, i.e. it flows wherever the pressure is lower. At those points where the vapor temperature falls below the boiling point of the working medium 23, it condenses. To do this, the vapor must give off heating energy H to the vessel and the vessel to the environment. This happens most strongly at the point where the condenser 11 is arranged, where active cooling can take place if necessary and a heat sink is provided.The temperature now stops dropping until the entire condensation enthalpy contained has been released into the environment, in this case to the heat exchanger 43 and the electrolysis storage 5 thermally coupled to it. The liquid portion of the working medium 23 returns to the evaporator 13 driven by gravity (thermosiphon). For the latter to function, the proportion of the working medium 23 in the liquid state must be lower there.

[0068] Since the vapor and liquid of the working medium 23 are located in the same encapsulated space, the system is in the wet vapor region. This means that at a specific pressure in the heat pipe 17, exactly a specific temperature exists. Since the pressure differences in a heat pipe 17 are very small, usually just a few Pascals, the resulting temperature difference between the evaporator 13 and the condenser 11 is also small, amounting to a maximum of a few Kelvin. A heat pipe 17 therefore has a very low thermal resistance. The region between the evaporator 13 and the condenser 11 is practically isothermal.

[0069] The gravity-driven heat pipe 17 is a two-phase thermosiphon or gravitational heat pipe. Here, the working medium 23 circulates independently due to gravity. As a result, the working medium 23 flows independently back into the evaporator 13. The heat H is supplied, in particular, only via the sump, i.e., up to the level of the liquid surface. This depends on the film formation by the returning liquid working medium 23.

Claims

Patent claims 1. Electrolysis system (100) comprising a wind turbine (1) and an electrolysis plant (5) which is connected to the wind turbine (1) for supplying electrolysis current, wherein an island network is implemented without connection to a supply network, further comprising a heat supply device (7) which is coupled to the electrolysis plant (5) and can be operated with a working medium (23), which has an evaporator (13) and a condenser (11), and which is designed such that in standstill operation, condensation heat of the working medium (23) can be transferred to the electrolysis plant (5) by means of the condenser (11), so that a temperature is maintained above a minimum temperature.

2. Electrolysis system (100) according to claim 1, wherein the heat supply device (7) comprises a gravity-driven heat pipe (17), wherein the condenser (11) is formed above the evaporator (13) on the heat pipe (17).

3. Electrolysis system (100) according to claim 1 or 2, wherein the heat supply device (7) comprises a deep probe (37) designed to extract heat from a deep heat reservoir (15), wherein the evaporator (13) is immersed in the heat reservoir (15).

4. Electrolysis system (100) according to one of the preceding claims, wherein the heat supply device (7) has a heat reservoir (15) which is formed within the tower (19) of the wind turbine (5).

5. Electrolysis system (100) according to one of the preceding claims, in which the heat supply device (7) comprises a heat pipe (17), wherein the evaporator (13) is connected to the condenser (11) via an adiabatic zone (39), so that an independent circulation of the working medium (23) in the heat pipe (17) is effected.

6. Electrolysis system (100) according to one of claims 2 to 5, with a working medium (23) introduced into the heat pipe (17) under a predetermined working pressure, so that an evaporation temperature in the range from 2°C to 10°C, in particular between 4°C and 8°C, is set under the working pressure.

7. Electrolysis system (100) according to one of claims 2 to 6, wherein the heat pipe (17) is designed as a CCy deep probe (37), with carbon dioxide (CO2) as the working medium (23).

8. Electrolysis system (100) according to claim 7, wherein the carbon dioxide (CO2) is introduced into the heat pipe (17) under a working pressure of 35 bar to 45 bar, in particular between 37 bar and 42 bar.

9. Electrolysis system (100) according to one of the preceding claims, in which an internal heat control (41) is provided for the heat transport, with a valve or a throttle as a control element, so that the forward and return flow of the working medium (23) can be controlled.

10. Electrolysis system (100) according to one of claims 3 to 9, wherein the evaporator (13) is arranged within the foundation (33) of the wind turbine (1), so that in the evaporator (13) evaporation of liquid working medium (23) is caused by deep heat.

11. Electrolysis system (100) according to one of the preceding claims, in which the electrolysis plant (5) has an electrolyzer arranged in a container (9) and a heat exchanger (11) which, in normal operation, is designed to dissipate process heat from the electrolysis from the container (9).

12. Electrolysis system (100) according to one of the preceding claims, in which a heat exchanger (11) is provided which is thermally coupled to the condenser (11) in such a way that, in standstill operation, condensation heat of the working medium (23) can be transferred to water-carrying components of the electrolysis system (5).

13. Electrolysis system (100) according to one of the preceding claims, comprising a wind turbine (1) with a tower (19) and with a platform (3) attached to the tower (19) on which an electrolysis system (5) is arranged.

14. Electrolysis system (100) according to claim 13, wherein the evaporator (13) is arranged in the underwater region (31) in deep water layers or in the seabed (35).

15. A method for operating an electrolysis system (100) according to one of the preceding claims, wherein in a standstill operation by means of the heat supply device (7) a working medium (23) is evaporated and evaporated working medium (23) is condensed, whereby condensation heat is generated and transferred to the electrolysis system (5), so that a temperature is maintained above a minimum temperature and freezing of water-carrying components of the electrolysis system (5) is prevented.

16. The method according to claim 15, wherein the temperature maintenance is initiated at an outside temperature of less than 5°C, wherein the working medium (23) is circulated in a gravity-driven heat pipe (17) and condensation heat is extracted from the working medium (23) and transferred to the water-carrying components of the electrolysis plant (5), so that freezing protection is brought about.

17. Method according to claim 15 or 16, wherein the heat flow is controlled by a control device (41), wherein the forward and return flow of the circulating working medium (23) is adjusted, whereby the condensation heat transferred to the electrolysis system (5) is adjusted.

18. The method according to any one of claims 15, 16 or 17, wherein in normal operation the electrolysis plant (5) is supplied with electrolysis current from the wind turbine (1), wherein process heat is discharged from the electrolyzer via a heat exchanger (11).

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