Energy system for providing electrical power

Abstract

An energy system (1) for providing electrical power to at least one consumer is described, comprising: - an electrolyzer (10) for the electrolytic decomposition of water (H2O) into oxygen (O2) and hydrogen (H2) using electrical energy (E), - an oxygen storage unit (31) for storing the electrolytically produced oxygen (O2) in liquefied form at a cryogenic temperature, - an internal combustion engine (40) and a generator (41) driven by the internal combustion engine (40) for providing electrical power by burning a fuel (F) in an oxyfuel process in which the electrolytically produced oxygen (O2) is used, and - at least one heat exchanger (21, 22) for transferring thermal energy between the electrolytically produced oxygen (O2) and at least one other process medium (PM), wherein the heat exchanger (21, 22) is designed toto be operated at least in a partial area at a cryogenic temperature of -35 °C or less. Furthermore, a method for providing electrical power is described.

Description

[0001] The present invention relates to an energy system for providing electrical power to at least one consumer, wherein the energy system comprises an electrolyzer, an oxygen storage device, and an internal combustion engine. The invention further relates to a corresponding method for providing electrical power.

[0002] Energy systems are known from the prior art in which water is electrolytically decomposed into oxygen and hydrogen, with the electrolysis products subsequently being used to generate electrical energy, thermal energy, and / or chemical synthesis products. Such energy systems can, for example, absorb electrical energy available from renewable energy sources and store it in another form (especially chemically) so that it can be made available in the desired form at a later time when needed, primarily as electrical energy. These energy systems are therefore particularly useful for compensating for fluctuations in the electrical power supplied to a power grid due to the fluctuating availability of renewable energies, or for adapting the supply to the demand profile for electrical power from consumers.Such an energy system is described, for example, in the publication entitled "Simulation Based Techno-Economic Evaluation of Self-sufficient Microgrid Systems with Renewable Energy and Power-to-X" by Z. Zhang et al. in P. Schossig et al. (Eds.): IRES 2022, AHE 16, pp. 551-562, 2023. Due to the inertia of large power plants, decentralized energy storage is increasingly being used to balance fluctuations in available electrical power. This involves a multitude of consumer-oriented energy systems, each capable of converting and storing enough energy to supply a smaller sub-branch of the power grid. This supply is intended to be sufficient, in particular, for the typical periods when little electrical power is directly available from renewable energy sources.Such decentralized energy systems are also referred to in the professional community as microgrid systems when they serve to supply locally delimited or at least locally delimitable power grids – the so-called microgrids. The described decentralized intermediate storage can be used not only in true island grids (i.e., microgrids in so-called "island mode," without a direct connection to a higher-level interconnected grid), but also in local subnetworks within more extensive interconnected grids (i.e., microgrids operating in so-called "grid-connected mode," with an electrical connection to the interconnected grid).

[0003] One difficulty with such energy systems is generally to achieve both high efficiency in the conversion of the individual forms of energy and to enable the intermediate storage of sufficiently large amounts of energy to compensate for fluctuations that occur.

[0004] The object of the invention is therefore to provide an energy system that simultaneously fulfills these two requirements. This energy system should, in particular, be feasible in the smallest possible space, so that storage within small, local subnetworks or island grids is possible. A further object is to provide a corresponding method for providing electrical power.

[0005] These problems are solved by the energy system described in claim 1 and the method described in claim 15.

[0006] The energy system according to the invention is designed to provide electrical power to at least one consumer. It comprises: an electrolyzer for the electrolytic decomposition of water into oxygen and hydrogen using electrical energy, an oxygen storage device for storing the electrolytically produced oxygen in liquefied form at a cryogenic temperature, an internal combustion engine and a generator driven by the internal combustion engine for providing electrical power by burning a fuel in an oxyfuel process in which the electrolytically produced oxygen is used, and at least one heat exchanger for transferring thermal energy between the electrolytically produced oxygen and at least one other process medium, wherein the heat exchanger is designed to operate at least in a partial area at a cryogenic temperature of -35 °C or to be operated less.

[0007] In this energy system, the electrolyzer can be operated advantageously when electrical energy is particularly inexpensive and / or when it is in surplus, for example, when a large amount of electrical energy from renewable energy sources such as photovoltaics or wind power is available, or when consumption is particularly low. At least the oxygen from the electrolysis products formed should be temporarily stored to allow for later use. According to the invention, this occurs in liquefied form at a cryogenic temperature. A cryogenic temperature is generally understood here to be a temperature of -182 °C or less. At such a temperature, oxygen exists in liquefied form at normal pressure.

[0008] The internal combustion engine is coupled to the generator to provide electrical power together through the combustion of a fuel. The combustion of the fuel is to take place in a so-called oxyfuel process. In the context of the present invention, an oxyfuel process is generally understood to be a combustion process in which a fuel is combusted together with an oxidizer gas, wherein the oxidizer gas has an oxygen content of at least 15% and a nitrogen content of at most 5%, preferably at most 1%, and particularly preferably at most 0.1%. In particular, the oxidizer gas can be essentially free of nitrogen. The oxygen content can advantageously be considerably higher, e.g., at least 21%, or even at least 25%, or even over 30%.It is not excluded within the scope of the invention that, in addition to oxygen, one or more other substances may also be present in the oxidation gas, in particular carbon dioxide. Other inert gases, such as noble gases, may also be present in small proportions, for example, up to 1% each.

[0009] In particular, the oxidation gas can essentially be a mixture of oxygen and carbon dioxide. Due to the absence of nitrogen (apart from minimal impurities), this type of combustion process ensures that the flue gas produced during combustion also has a low nitrogen content or is even essentially nitrogen-free (at least if the fuel used is also essentially nitrogen-free). This eliminates the need for a catalyst for flue gas aftertreatment, as virtually no nitrogen oxides are formed during combustion. The comparatively high oxygen content in the oxyfuel process allows for high flame temperatures compared to combustion with air.If the oxidizing gas is pure oxygen or a mixture of oxygen and carbon dioxide, the oxyfuel process is particularly suitable for recovering the carbon dioxide contained in the flue gas after combustion, since in this case the flue gas is essentially a mixture of carbon dioxide and water vapor (possibly with a proportion of unreacted oxygen, which is present in excess during combustion to ensure complete combustion). In particular, the flue gas contains only small amounts of other gases (so-called extraneous gases) such as nitrogen or argon. This facilitates the recovery and reintegration of the carbon dioxide contained in the flue gas into the energy system processes, as, in particular, no separation of carbon dioxide and nitrogen is then necessary.

[0010] The generator coupled to the internal combustion engine can provide electrical power for one or more consumers. The internal combustion engine and generator are particularly advantageous when relatively little electrical energy is available. In the oxyfuel process, oxygen is used that was previously produced electrolytically from a surplus of electrical energy and stored in liquid form.

[0011] The heat exchanger serves to either heat or cool the electrolytically produced oxygen, thereby cooling or heating another process medium within the energy system. Specifically, it is a heat exchanger designed for indirect heat transfer between two spatially separated fluid streams. The heat exchanger should operate at least in a portion of its operation at a cryogenic temperature; in particular, the oxygen to be heated is raised from a cryogenic temperature to a higher temperature, or the oxygen to be cooled is cooled to a cryogenic temperature. A cryogenic temperature is generally understood to be -35 °C or lower.Particularly advantageous is the ability to operate at temperatures below -50 °C in the relevant section of the heat exchanger, and especially at cryogenic temperatures, where oxygen is in liquid form. Using such a heat exchanger for heating and / or cooling the stored oxygen allows for storage in liquid form with comparatively high overall energy efficiency. When oxygen is liquefied primarily through adiabatic compression using a compressor, a significant amount of energy is required to operate the compressor. Liquefaction is considerably more energy-efficient if a process medium already present in cryogenic form during the operation of the energy system can be used to cool the oxygen and thus at least partially support the liquefaction process.Alternatively or additionally, the oxygen present in liquid form during intermediate storage can be used to cool another process medium and, in particular, to at least support its liquefaction. In this way, the "coldness" of the oxygen or the other process medium can be further utilized as a resource in the energy system.

[0012] A key advantage of the energy system according to the invention is that the electrolytically produced oxygen can be cryogenically stored in an energy-efficient manner. Storing oxygen in liquid form is particularly advantageous because of the significantly smaller storage space required, as liquid oxygen requires a much smaller storage volume than a pressurized storage system at ambient temperature. Furthermore, considerably less material is needed to manufacture the storage system than a pressurized one. Due to the risk of explosion, the pressure of such a warm oxygen storage system is typically limited to 300 bar, which further increases the required storage volume compared to other gases. The advantage of the smaller storage volume is particularly beneficial in smaller, decentralized energy systems, where space is typically limited.Another advantage of cryogenic storage of oxygen is the reduction of the risk of explosion.

[0013] The method according to the invention serves to provide electrical power to at least one consumer. It comprises the following steps: a) electrolytic decomposition of water into oxygen and hydrogen using electrical energy, b) storage of the electrolytically produced oxygen in liquefied form at a cryogenic temperature, c) combustion of a fuel in an oxyfuel process in which the electrolytically produced oxygen is used, within an internal combustion engine and provision of electrical power by means of a generator coupled to the internal combustion engine.

[0014] In this process, thermal energy is transferred between the electrolytically produced oxygen and at least one other process medium using a heat exchanger, wherein the heat exchanger is operated at a cryogenic temperature of -35 °C or less, at least in a partial section. The advantages of the process according to the invention are analogous to the advantages of the energy system according to the invention described above. The process is carried out in particular with the energy system according to the invention.

[0015] Advantageous embodiments and further developments of the invention will become apparent from the claims dependent on claim 1 and the following description. The described embodiments of the energy system can also be implemented in the method, and vice versa.

[0016] The energy system can thus advantageously comprise a plurality of heat exchangers, wherein, in particular, at least one heat exchanger is designed to cool the electrolytically produced oxygen to a cryogenic temperature and at least one further heat exchanger is designed to heat the electrolytically produced oxygen from a cryogenic temperature to a higher temperature. This configuration achieves particularly high energy efficiency, since both when cooling the oxygen, available cooling from another process medium can be used, and when heating the oxygen before use in the oxyfuel process, the cooling effect present in the oxygen can be used to cool another process medium. In principle, several heat exchangers can be provided for each of the heating and / or cooling of the oxygen.Alternatively or additionally, a multi-stage heat exchanger can also be provided in the respective path.

[0017] According to a particularly advantageous embodiment, at least one of the present heat exchangers can be configured to be permeated, at least in a partial region, by a cryogenic fluid, in particular by electrolytically produced liquid oxygen. In other words, the heat exchanger is designed to be operated at a cryogenic temperature, at least in the aforementioned partial region. It is particularly advantageous that, during operation of the energy system, gaseous oxygen can condense within a heat exchanger as it cools, and that the other process medium can evaporate as it heats up. Alternatively or additionally, another process medium can condense within a heat exchanger as it cools, and that the liquid oxygen can evaporate as it heats up. In this way, the liquefaction of oxygen or...the other process medium can be carried out in a particularly energy-efficient manner.

[0018] According to a first embodiment, at least one of the heat exchangers is designed to cool the electrolytically produced oxygen to a cryogenic temperature. The process medium to be heated is, in particular, either liquid nitrogen or liquid carbon dioxide. Liquid nitrogen is a particularly easy-to-handle and relatively inexpensive cryogen, whose coldness can be used to liquefy oxygen. The nitrogen evaporated during the heat exchange can optionally be used for other purposes within the energy system, for example, for the synthesis of ammonia together with the electrolytically produced hydrogen. Carbon dioxide is also comparatively easy to handle and is, for example, in liquid form at a pressure slightly above 5.2 bar, at a temperature in the range of -56 °C to -20 °C.Such a low temperature level can at least be used to pre-cool oxygen during liquefaction. Carbon dioxide can already be present in the energy system as a process gas and can be recovered, in particular, from the combustion process. Before further use, it can be stored, at least partially, in a space-saving manner in liquefied form.

[0019] Alternatively or additionally, according to a second embodiment, at least one of the heat exchangers can be designed to heat the electrolytically generated oxygen from a cryogenic temperature. The process medium to be cooled can be, in particular, carbon dioxide. The carbon dioxide can advantageously be liquefied. Here, too, it can be, in particular, carbon dioxide recovered from combustion, which is stored in a space-saving liquefied form before further use, with the cold of the cryogenic oxygen being used to assist in the liquefaction process.

[0020] According to a preferred embodiment, at least one of the existing heat exchangers can be manufactured using an additive manufacturing process. The term "additive manufacturing process" is defined here, in accordance with the industry standard ASTM F2792, as a process in which material is applied sequentially and bonded to preceding material layers to create a three-dimensional body according to a predefined three-dimensional geometric model. This contrasts with conventional subtractive manufacturing processes, in which a three-dimensional body is obtained by removing material from a blank (for example, by milling, grinding, and / or drilling). An advantage of such an additively manufactured heat exchanger is that it allows for the creation of fine and complex structures within the thermal interaction zone of the two fluid flows.This allows for particularly efficient heat transfer. Generally, and regardless of the manufacturing process used, at least one of the heat exchangers can be a counterflow heat exchanger. Furthermore, it can be advantageous if at least one of the heat exchangers is designed as a multi-stage heat exchanger.

[0021] According to a generally preferred embodiment, the energy system can be a multimodal energy system. This is understood to mean an energy system that, in addition to providing electrical power, also serves to provide chemical substances and / or heat and / or cooling power. According to a first advantageous embodiment of such a multimodal energy system, it comprises at least one synthesis reactor for producing at least one synthesis product from the electrolytically produced hydrogen and at least one other reactant. The synthesis product can, for example, be a hydrogen-containing product. Such an optionally included synthesis reactor can also preferably be manufactured using an additive manufacturing process, which in turn offers advantages with regard to fine and complex internal structures for guiding the material flows involved.

[0022] In this embodiment, the synthesis reactor can be particularly advantageously designed for the reaction of hydrogen with carbon dioxide. In other words, carbon dioxide is then used as an additional reactant, although the possibility of using further reactants is not excluded. Most preferably, the synthesis reactor can be configured for the production of a carbon-based synthetic fuel. Such a synthetic fuel is also generally referred to as an e-fuel. It can comprise one or more compounds of the general formula CnHmOz, where n and m are preferably 1 or greater, and z can in particular also be 0 or take on a value of 1 or more. The synthetic fuel can in particular comprise one or more of the following compounds: Methane, ethane, propane, butane or another saturated hydrocarbon, methanol or another alcohol, dimethyl ether or another ether, oligomethyl ether or other polyethers, ethylene, propylene or another unsaturated hydrocarbon, so-called Fischer-Tropsch products such as aliphatic linear hydrocarbons with 8 to 20 carbon atoms.

[0023] Such a synthetic fuel can, for example, be used (in whole or in part) in step c) as fuel for the internal combustion engine in the oxyfuel process. Alternatively, a comparatively high-quality synthesis product can also be produced in the synthesis reactor (e.g., as a raw material for the chemical industry), making combustion uneconomical and allowing the use of a different fuel in step c). Combinations of these two options are also possible, for example, if the availability of fuels from other sources fluctuates and / or the quantity of the synthesis product produced temporarily exceeds other demand.

[0024] Alternatively or additionally to such a carbon-based synthesis stage, the energy system can include a synthesis reactor designed to produce ammonia by reacting hydrogen with nitrogen as a further reactant. This variant is particularly advantageous in combination with the use of liquid nitrogen as a cryogenic coolant, because the nitrogen used for cooling can then be used as a reactant for synthesis after its evaporation. This dual use, in turn, makes the overall process particularly resource-efficient. The synthesis product, ammonia, can be used in the chemical industry as a raw material for the production of other nitrogen compounds or as a fertilizer in agriculture. Alternatively, ammonia can also be used as a synthetic fuel.The synthesis product ammonia can also be stored in liquefied form. An additional heat exchanger can be used for the liquefaction of the ammonia and / or the cooling of its reactants. In particular, this additional heat exchanger can be designed to cool ammonia and / or its reactants while simultaneously heating pure nitrogen and / or carbon dioxide. Alternatively, instead of using it for ammonia synthesis, the gaseous nitrogen produced from the evaporation of the liquid nitrogen used in the heat exchanger can be recycled as a refrigerant. It can be liquefied using a high-pressure compressor and returned to the cycle. A combination of both options is also conceivable, with the proportion of each application adjusted depending on the available resources.

[0025] According to a second advantageous embodiment of the multimodal energy system, the internal combustion engine can be a combined heat and power (CHP) machine, which, in addition to driving the generator, can provide heat output for a consumer. In other words, the thermal energy from combustion is utilized similarly to a combined heat and power plant and supplied to a consumer as heat output. This can optionally occur in addition to the provision of one or more synthesis products, so that the energy system then generates a total of three different types of output: electrical power, heat output, and one or more synthesis products.

[0026] In principle, various fuels can be used for combustion in an internal combustion engine: This can be either the aforementioned synthetic fuel or another fuel such as a fossil fuel like natural gas or butane-propane liquefied petroleum gas (LPG), diesel, or heating oil, or even another renewable fuel such as combustible biogas from a biogas plant. The fuel can also be a synthesis gas with the main components hydrogen (H₂), carbon monoxide (CO), and carbon dioxide (CO₂) from the thermochemical conversion (especially a gasification reaction) of a high-calorific-value, carbon-containing feedstock with a total composition CXH₂Y O₂ZN₂U₆Si₆, containing pure oxygen (O₂) and water vapor (H₂O).When using the oxyfuel process with an increased oxygen content (compared to air), fuels with low energy content can also be used advantageously, e.g. a so-called low-energy gas with a calorific value of 7100 kJ / Nm 3< or less.

[0027] A particularly advantageous aspect of this process is that the internal combustion engine can be connected to a device for recovering carbon dioxide from the flue gas produced during combustion. In other words, the process allows for the recovery of carbon dioxide, which can then be temporarily stored in liquefied form, particularly after heat exchange with cryogenic oxygen. The liquefied carbon dioxide, especially after heating (again advantageously via heat exchange with oxygen and / or another process medium), can be fed into a synthesis reactor as a feedstock for carbon-based synthesis. Alternatively or additionally, the recovered carbon dioxide can also be fed back into the internal combustion engine, and cryogenic storage is generally not necessary for this portion.This is because this type of reuse can occur in the same operating mode as the recovery of carbon dioxide, namely during the combustion process. Generally, and regardless of the type of reuse, the carbon dioxide can be almost completely recovered from the flue gas produced.

[0028] In this embodiment, it is particularly advantageous for the internal combustion engine to be designed to burn the fuel with a mixture of electrolytically produced oxygen and carbon dioxide recovered from the flue gas. In other words, an oxidizer gas is used for combustion that consists predominantly or even primarily of oxygen and carbon dioxide. Advantageously, the proportions of oxygen and carbon dioxide in such a mixture can be adjusted to the prevailing conditions of the combustion process. For example, the combustion temperature can be controlled by changing the mixture ratio. Similarly, if the composition of the fuel used changes, the composition of the oxidizer gas can be adjusted accordingly, for example, to maintain a predetermined combustion temperature even with fluctuations in the fuel composition.

[0029] Due to the comparatively high oxygen content in the oxidation gas and the combustion temperature, which can be controlled via the mixture ratio, the formation of polycyclic aromatic hydrocarbons and / or other volatile organic compounds during combustion can be advantageously kept low. Because the oxygen content in the oxidation gas can be metered, an exhaust gas turbocharger can also be advantageously omitted, since an increase in the oxygen content of the mixture can be achieved instead of (or in addition to) a pressure increase. If an exhaust gas turbocharger is omitted, the flue gas is available at a comparatively higher pressure. This can have a positive effect on carbon dioxide recovery, especially because less intensive compression is then required for the liquefaction of the recovered carbon dioxide.In general, the internal combustion engine can also be operated without an exhaust gas turbocharger at a comparatively high boost pressure, since the oxygen evaporated from the liquid form is available at a relatively high pressure and the carbon dioxide-containing exhaust gas stream also has a high residual pressure.

[0030] Preferably, when using recovered carbon dioxide, the oxidation gas is essentially free of nitrogen. The internal combustion engine can then be designed for nitrogen-free combustion of the fuel. In other words, the fuel used can also be essentially free of nitrogen. Then, no nitrogen oxides are formed during combustion, and a catalyst can be omitted.

[0031] Furthermore, in connection with carbon dioxide recovery, it is advantageous if both the fuel and the supply of electrolytically generated oxygen contain only small amounts of other inert gases, particularly noble gases, as impurities. For example, the mole fraction of the noble gases can be in the range of less than 1% and preferably even less than 0.1% in order to avoid a gradual accumulation of these substances within the closed carbon dioxide cycle.

[0032] Generally advantageous is the energy system's ability to switch between a first and a second operating mode. The first operating mode serves to... a) To split water into hydrogen and oxygen using the electrolyzer and electrical energy, b) and to store oxygen in liquid form in the oxygen storage tank. In contrast, the second operating mode serves to c) burn fuel in the internal combustion engine using the oxyfuel process, whereby the generator is driven by the internal combustion engine and electrical power is provided by the generator, and electrolytically produced oxygen is consumed from the oxygen storage tank.

[0033] In other words, in the first operating mode, at least steps a) and b) of the process according to the invention are carried out, and in the second operating mode, at least step c) of the process is carried out. The first operating mode is particularly advantageous when a large amount of electrical energy is available and relatively little electrical power is drawn by the consumers. In this case, at least the oxygen as a product of electrolysis can be temporarily stored in liquid form for later use. In this first operating mode, the optional synthesis reactor can also be advantageously operated, so that one or more synthesis products can also be stored. Alternatively, the electrolytically produced hydrogen can also be stored.Accordingly, the second operating mode is primarily used when little electrical energy is available and consumers are demanding a comparatively high amount of electrical power. In this second operating mode, the optional liquid carbon dioxide storage tank can also be filled in the versions that recover carbon dioxide from combustion.

[0034] A heat exchanger designed to cool oxygen while simultaneously heating another process medium is advantageously used primarily in the first operating mode. A heat exchanger designed to heat oxygen while simultaneously cooling another process medium is correspondingly advantageous in the second operating mode. However, the essential point in relation to the invention is only that at least one heat exchanger is present in the flow of electrolytically produced oxygen. Furthermore, the two described operating modes need not necessarily be mutually exclusive. Transitional phases are also conceivable, in which, for example, the electrolysis and storage of the electrolytically produced oxygen are still active and the operation of the internal combustion engine is being started up, or vice versa.

[0035] The invention is described below with reference to some preferred embodiments and the attached drawings, in which: Figure 1 a schematic diagram of an energy system according to a first example of the invention shows, Figure 2 A second example of an energy system, which includes a synthesis reactor, is shown. Figure 3 A third example of an energy system with an alternative synthesis reactor shows, Figure 4 a fourth example of an energy system shows and Figure 5 and 6 The fourth example shows two different operating states of the energy system.

[0036] In the figures, identical or functionally equivalent elements are provided with the same reference symbols.

[0037] In Figure 1Figure 1 shows a schematic diagram of an energy system 1 according to a first example of the invention. This diagram is highly simplified and shows only the essential components. The energy system 1 comprises an electrolyzer 10, with which water (H₂O) can be electrolytically split into oxygen (O₂) and hydrogen (H₂). This occurs by consuming electrical energy (E), which can, for example, originate from a renewable energy source or, during periods of low electricity prices, from the electricity grid. The water (H₂O) can be supplied to the electrolyzer 10 in deionized form. The electrolytically produced hydrogen (H₂) can be used in various ways. For example, it can be used within the energy system 1 as a reactant for a chemical synthesis, or it can be stored in a hydrogen storage system for later use elsewhere, e.g., in a hydrogen storage facility.The oxygen produced electrolytically is used as fuel for a fuel cell or fed into a hydrogen network. The oxygen produced electrolytically, on the other hand, is temporarily stored in liquid form in an oxygen storage unit 31 for use within the same energy system 1. For this purpose, the oxygen is cooled to a cryogenic temperature, i.e., a temperature below its boiling point at normal pressure.

[0038] Energy system 1 also includes an internal combustion engine 40 and a generator 41 coupled to it. A fuel F, supplied from a fuel storage unit 60, can be burned in the internal combustion engine 40. This fuel can be, for example, a liquid or a gaseous fuel. It can be a fossil fuel such as natural gas or petroleum, or a fuel from renewable sources such as biogas or a synthetic fuel. The fuel can also be a synthesis gas with the main components hydrogen H₂, carbon monoxide CO, and carbon dioxide CO₂ from the thermochemical conversion (in particular a gasification reaction) of a high-calorific-value, carbon-containing feedstock with a total composition CXH₂Y O₂Z N u Si₂V, with pure oxygen O₂ and water vapor H₂O. The fuel F can generally be carbon-containing.Generator 41 can be driven by the internal combustion engine 40, so that electrical power can be provided to a consumer when the fuel is burned via generator 41. Thus, in this part of the energy system, the chemical energy of the fuel F is converted into electrical energy E. Combustion within the internal combustion engine 40 is carried out according to the oxyfuel process, so that a gas with a particularly high oxygen content is used as the oxidation gas OG. The oxygen O₂ for this oxidation gas is taken (at least partially) from the described cryogenic oxygen storage 31; it is therefore electrolytically produced oxygen. The unlabeled arrow in the right part of the figure indicates that, in addition to this oxygen O₂, another component, in particular carbon dioxide, may be added to the oxidation gas OG.

[0039] The energy system 1 according to the invention is characterized in that the electrolytically produced oxygen O₂ is stored in liquefied form and that a heat exchanger is used when cooling the oxygen to a cryogenic temperature and / or when heating the oxygen from the cryogenic temperature. By way of example, Figure 1 Two such heat exchangers 21 and 22 are shown, namely a first 21 in the oxygen cooling path and a second 22 in the oxygen heating path. However, to realize the invention, it is generally sufficient if a heat exchanger is used in only one of these two paths.

[0040] The heat exchanger 21 is permeated by initially warm oxygen (O₂) and by another process medium (PM), which is initially colder than the incoming warm oxygen. This PM can therefore be a fluid (i.e., liquid and / or gaseous) process medium that advantageously fulfills an additional function within the energy system 1. The oxygen (O₂) is cooled as it passes through the heat exchanger, preferably to a cryogenic temperature of -35 °C or less. It is also possible for the oxygen to be cooled to a cryogenic temperature below its boiling point in this heat exchanger 21 and thus condense within the heat exchanger itself. However, this can only be achieved with certain cryogenic process media, and in particular with liquid nitrogen as the PM.Cooling the oxygen to a cryogenic temperature directly in heat exchanger 21 is not strictly necessary. To achieve high energy efficiency during the operation of energy system 1, it is sufficient if the oxygen is pre-cooled to a very low temperature in this heat exchanger 21 and then liquefied in a further step not explicitly shown here.

[0041] The heat exchanger 22 is permeated by initially cold oxygen (O₂) and by another process medium (PM), which is initially warmer than the incoming cold oxygen. This process medium can also be a fluid, which advantageously fulfills an additional function within the energy system 1. As the oxygen (O₂) passes through the heat exchanger, it is heated from a very low temperature to a higher temperature, with the initially low temperature being used to cool the PM. It is also possible for the oxygen to evaporate from its liquefied form in this heat exchanger 22. Optionally, the process medium to be cooled can condense and, in particular, be liquefied within it, which facilitates subsequent storage of this process medium.

[0042] Energy system 1 according to Figure 1It can be operated in two different operating modes. The first operating mode is used when, for example, a large amount of electrical energy E is available in a higher-level power grid. The electrolyzer 10 is then operated with this energy E, and the oxygen produced is stored in the oxygen storage tank 31. In the first operating mode, the components in the left half of the Figure 1 active. Conversely, the second operating mode comes into play when the electrical energy required by the consumers exceeds the supply from other sources. Then the internal combustion engine 40 is operated, with the coupled generator 41 providing electrical power for the consumers. This is done using oxygen from the oxygen storage tank 31. In the second operating mode, the components in the right half of the Figure 1active. At least in one of these halves, and thus also in one of the two operating modes, a heat exchanger 21 and / or 22 is used in the oxygen path.

[0043] In Figure 2 A similar schematic diagram of an energy system 1 according to a second example of the invention is shown. This energy system 1 is based on the basic design of the Figure 1and is extended by several optional components. For example, the electrolytically produced hydrogen H₂ is fed to a synthesis reactor 71 as a reactant. If necessary, the hydrogen H₂ can be compressed using a compressor 90. Carbon dioxide CO₂ is also fed to the synthesis reactor 71 as a further reactant. Thus, a carbon-based synthesis takes place in which the carbon dioxide is reduced by the hydrogen, resulting in the formation of a synthetic fuel in this example. In general, the synthesis product can be a compound with the molecular formula CₙHₙO₂z, or the synthesis product can comprise one or more compounds with such a molecular formula, where z can optionally be 0. The resulting fuel EF can be stored in a fuel storage tank 81. The carbon dioxide fed to the synthesis reactor 71 is, in this example, Figure 2Carbon dioxide is recovered from combustion and subsequently stored in a carbon dioxide storage unit 32. For storage, the carbon dioxide is liquefied and therefore cooled to a cryogenic temperature, e.g., in the range of approximately -50 °C. This cryogenic carbon dioxide flows through a heat exchanger 21a and is heated there, while the oxygen also flowing through this heat exchanger 21a is cooled. At the temperature of liquid carbon dioxide, however, the oxygen does not yet liquefy, but only cools significantly. Therefore, in this example, liquefaction on the further path to the oxygen storage unit 31 can be achieved by a separate device, which is not shown separately here. Overall, in the first operating mode, the components in the left half of the Figure 2 active.

[0044] In the second operating mode, the components in the right half of the figure are active, and fuel 60 is again burned in the internal combustion engine 41. This can optionally be (at least partially) the synthetic fuel EF, which was produced from hydrogen and carbon dioxide in the first operating mode. Alternatively, however, fuel F from other sources can also be used. The flue gas RG formed during combustion is directed into a recovery device 50, where the carbon dioxide contained in the flue gas is recovered. This recovery device 50 can, in particular, include a dehumidification device to remove water produced during combustion from the flue gas. The recovered carbon dioxide can now be utilized in various ways, and the ratio of the two utilization pathways can be adjusted, if necessary, even during the process.The recovery device 50 can thus include a connection for a cold partial flow extraction, with which comparatively cold carbon dioxide is extracted and mixed in a first path with the oxygen flowing towards the machine 40, thereby forming the oxidation gas OG supplied to the combustion. The mixing ratio of these two components in the oxidation gas OG can, in turn, be adapted to the other boundary conditions of the combustion and, in particular, varied during the course of the process. For example, a fermentation gas or synthesis gas can be used as fuel F, which already contains carbon dioxide. This carbon dioxide does not have to be removed from the fermentation gas or synthesis gas; rather, the amount of additionally supplied carbon dioxide can be adjusted so that the desired concentration and, for example, the desired flame temperature and power output during combustion are achieved.

[0045] For the second utilization pathway, the carbon dioxide is extracted from the recovery device 50, for example, at a comparatively higher temperature level, and first compressed by a compressor 90 before being fed to the heat exchanger 22 as a further process medium. Initially warm carbon dioxide and initially cold oxygen flow into the heat exchanger 22, whereby the oxygen is heated and the carbon dioxide is cooled. The incoming oxygen can, in particular, still be liquefied or, more generally, at a very low temperature. The carbon dioxide can liquefy due to heat transfer, which is possible especially at a pressure above 5.2 bar. In the area of ​​the outlet for liquefied carbon dioxide, the heat exchanger 22 can advantageously have a degassing device with which oxygen and other lower-boiling impurities, such as...Nitrogen and noble gases can also be removed from the liquid carbon dioxide. The liquefied carbon dioxide is then fed into the carbon dioxide storage tank 32, from which it can be consumed in the first operating mode as described.

[0046] In Figure 3 A similar schematic diagram of an energy system 1 according to a third example of the invention is shown. This energy system 1 is also based on the basic design of the Figure 1 and is extended by several optional components. Similar to the example of the Figure 2Here too, carbon dioxide is recovered from the flue gas RG of the combustion process and partly fed to the oxidation gas OG, while the remainder is used for other purposes. This alternative use is not shown for clarity, but liquefaction of the carbon dioxide in heat exchanger 22 can also occur here. In this example as well, the electrolytically produced hydrogen H₂ is utilized in a hydrogen-based synthesis in the first operating mode. For this purpose, the hydrogen is fed to a synthesis reactor 72, which in this example is configured for the synthesis of ammonia NH₃ and is accordingly fed with nitrogen N₂ as a further reactant. Optionally, further components can be located upstream of this synthesis reactor 72, such as a reactor for a catalytic reaction, in which any residual oxygen content in the incoming hydrogen is removed by catalytic reaction with hydrogen and condensation of the water formed.The ammonia (NH3) produced is stored in an ammonia storage tank 82, which may optionally have additional components for purifying, compressing, and / or cooling the ammonia. Here, too, a heat exchanger can be used, for example, to cool the ammonia to a cryogenic temperature and heat another process medium, thus enabling the storage of the ammonia in liquefied form without an additional compressor.

[0047] The energy system of the system includes the cooling of the electrolytically produced oxygen. Figure 3A heat exchanger 21b, into which liquid nitrogen N₂ flows from a nitrogen storage tank 33 as a further process medium, is used. The initially liquid nitrogen is heated in the heat exchanger 21b, and the initially warm oxygen is cooled to a cryogenic temperature, which may cause it to condense directly in the heat exchanger 21b. This advantageously allows the electrolytically produced oxygen to be liquefied without an additional compressor on its way to the oxygen storage tank 31. The incoming liquid nitrogen N₂ evaporates in the heat exchanger and is then fed to the synthesis reactor 72 as a reactant, thus enabling dual use of this process medium as well. Optionally, at least some of the evaporated nitrogen can be recompressed by a compressor 90 and fed back to the nitrogen storage tank 33 as liquid nitrogen in a closed loop.For this purpose, compressor 90 in the nitrogen path is suitably designed as a high-pressure compressor, whereby the compressed gas is cooled to a relatively low temperature, e.g., between -30 °C and -50 °C. This is followed by expansion, which can be carried out either adiabatically or, if necessary, via an expansion turbine, ultimately leading to the liquefaction of the nitrogen. This reliquefaction is particularly relevant when more liquid nitrogen is required in heat exchanger 21b than is subsequently consumed in ammonia synthesis. Similarly, in other embodiments, the nitrogen can be recycled in a closed refrigerant cycle where no reactor for ammonia synthesis is present.

[0048] In Figure 4A similar schematic diagram of an energy system 1 according to a fourth example of the invention is shown, in which the additional components of the two preceding examples are combined. In summary, both a carbon-based synthesis in synthesis reactor 71 and a nitrogen-based synthesis in synthesis reactor 72 are carried out here. The electrolytically generated oxygen O₂ is sequentially cooled using two successive heat exchangers 21a and 21b and is thereby liquefied in the second heat exchanger 21b. Carbon dioxide CO₂ recovered from combustion serves as a further process medium in the first heat exchanger 21a, and liquid nitrogen N₂ is introduced into the second heat exchanger as a further process medium. After passing through the respective heat exchangers, both substances are used as reactants in the respective synthesis reactors.For clarity, the carbon dioxide flow is shown here as a dashed line. The recovery and further use of the carbon dioxide is analogous to the example of [missing example]. Figure 2 For a better understanding of this fourth embodiment, the following are explained in Figure 5 Only those components that are active in the first operating mode are shown, and in Figure 6 only those components that are active in the second operating mode are shown.

[0049] The energy systems shown can optionally include further components, such as additional cooling or heating devices, compressors, condensation stages, dehumidification stages, and / or purification stages. For example, the recovered carbon dioxide can be purified of impurities that would interfere with synthesis reactor 71, such as oxygen and sulfur. The nitrogen evaporated in heat exchanger 21b can be purified of impurities that would interfere with synthesis reactor 72, such as sulfur, carbon monoxide, and carbon dioxide. Furthermore, the electrolytically produced gases oxygen and hydrogen can each first pass through a droplet separator for dehumidification. These droplet separators can each be connected to a cooling water circuit, which can also be used to cool the synthesis reactors.The cooling water can, for example, have a temperature of a few degrees above freezing. The cooling from this cooling water circuit can also be integrated into a building cooling system, thus relieving the load on a conventional air conditioning system with a compressor. The energy system can additionally include a heat pump (not shown here) or another heating device to heat certain components for operation, such as the optional reactor for the catalytic reaction of residual oxygen with hydrogen before the hydrogen is fed into the ammonia synthesis process. The electrolyzer 10, the combustion engine 40, and / or one of the synthesis reactors 71, 72 can serve as a heat reservoir, as thermal energy is released during operation, making heat dissipation advantageous. Cryogenic gas streams can also be used further in general, e.g.,for freezing water from oxygen or carbon dioxide before liquefaction, or for providing cooling power to a consumer, e.g. for building cooling.

[0050] The applicant points out at this point that, regardless of the grammatical gender of a particular personal term, it should always include persons with male, female and other gender identities. Reference symbol list

[0051] 1 Energy system 10 Electrolyzer 21 Heat exchanger for oxygen cooling 21a (first) Heat exchanger 21b (second) Heat exchanger 22 Heat exchanger for oxygen heating 31 Oxygen storage 32 Carbon dioxide storage 33 Nitrogen storage 40 Internal combustion engine 41 Generator 50 Recovery device 60 Fuel storage 71 Synthesis reactor for carbon-based synthesis 72 Synthesis reactor for nitrogen-based synthesis 81 Storage for synthetic fuel 82 Ammonia storage 90 Compressor CO₂ Carbon dioxide E Electrical energy EF Synthetic fuel F Fuel H₂O Water H₂ Hydrogen N₂ Nitrogen NH₃ Ammonia O₂ Oxygen O₂ Oxidation gas PM Other process medium R Flue gas

Claims

1. An energy system (1) for providing electrical power for at least one consumer, comprising: - an electrolyzer (10) for the electrolytic decomposition of water (H2O) into oxygen (O2) and hydrogen (H2) using electrical energy (E), - an oxygen storage device (31) for storing the electrolytically generated oxygen (O2) in liquefied form at a cryogenic temperature, - an internal combustion engine (40) and a generator (41) driven by the internal combustion engine (40) for providing electrical power by combustion of a fuel (F) in an oxyfuel process in which the electrolytically generated oxygen (O2) is used, and - at least one heat exchanger (21, 22) for transferring thermal energy between the electrolytically generated oxygen (O2) and at least one other process medium (PM), wherein the heat exchanger (21, 22) is designed toto be operated at least in part at a cryogenic temperature of -35 °C or less.

2. Energy system (1) according to claim 1, wherein at least one of the heat exchangers (21, 22) is designed to be flowed through at least in a partial area by electrolytically produced liquid oxygen (O2).

3. Energy system (1) according to claim 1 or 2, wherein at least one of the heat exchangers (21) present is designed to cool the electrolytically produced oxygen (O2) to a cryogenic temperature, wherein the process medium (PM) to be heated is either liquid nitrogen (N2) or liquid carbon dioxide (CO2).

4. Energy system (1) according to one of the preceding claims, in which at least one of the heat exchangers (22) is designed to heat the electrolytically produced oxygen (O2) from a cryogenic temperature, wherein the process medium (PM) to be cooled is carbon dioxide (CO2).

5. Energy system (1) according to one of the preceding claims, in which at least one of the present heat exchangers (21, 22) is a heat exchanger manufactured according to an additive manufacturing process.

6. Energy system (1) according to one of the preceding claims, comprising: - at least one synthesis reactor (71, 72) for producing at least one synthesis product (EF, NH3) from the electrolytically produced hydrogen (H2) and at least one further reactant (CO2, N2).

7. Energy system (1) according to claim 6, which comprises a synthesis reactor (71) which is designed to react hydrogen (H2) with carbon dioxide (CO2) as a further reactant.

8. Energy system (1) according to one of claims 6 or 7, wherein the synthesis reactor (71) is designed to form a carbon-based synthetic fuel (EF).

9. Energy system (1) according to one of claims 6 to 8, which comprises a synthesis reactor (72) for the formation of ammonia (NH3), wherein the synthesis reactor (72) is designed for the reaction of hydrogen (H2) with nitrogen (N2) as a further reactant.

10. Energy system (1) according to one of the preceding claims, in which the internal combustion engine (40) is a combined heat and power machine with which, in addition to driving the generator (41), heat output can be provided for a consumer.

11. Energy system (1) according to one of the preceding claims, in which the internal combustion engine (40) is connected to a device (50) for recovering carbon dioxide (CO2) from the flue gas (RG) formed during combustion.

12. Energy system (1) according to claim 11, wherein the internal combustion engine (40) is designed to combust the fuel (F) with a mixture of electrolytically generated oxygen (O2) and carbon dioxide (CO2) recovered from the flue gas (RG).

13. Energy system (1) according to one of the preceding claims, in which the internal combustion engine (40) is designed for nitrogen-free combustion of the fuel (F).

14. Energy system (1) according to one of the preceding claims, which is switchable between a first and a second operating mode, wherein the first operating mode serves to - decompose water (H2O) by means of the electrolyzer (10) using electrical energy (E) into hydrogen (H2) and oxygen (O2), - and to store oxygen (O2) in liquefied form in the oxygen storage (31), and wherein the second operating mode serves to - burn fuel (F) in the internal combustion engine (40) using the oxyfuel process, wherein the generator (41) is driven by the combustion engine (40) and electrical power is provided by the generator (41) and electrolytically produced oxygen (O2) from the oxygen storage (31) is consumed.

15. A method for providing electrical power for at least one consumer, comprising the following steps: a) electrolytic decomposition of water (H2O) into oxygen (O2) and hydrogen (H2) using electrical energy (E), b) storage of the electrolytically produced oxygen (O2) in liquefied form at a cryogenic temperature, c) combustion of a fuel (F) in an oxyfuel process, in which the electrolytically produced oxygen (O2) is used, within an internal combustion engine (40) and provision of electrical power by means of a generator (41) coupled to the internal combustion engine (40), - wherein thermal energy is transferred between the electrolytically produced oxygen (O2) and at least one other process medium (PM) using a heat exchanger (21, 22), wherein the heat exchanger (21, 22) is operated at a cryogenic temperature of -35 °C or less, at least in a partial region.

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