HIGH-TEMPERATURE CO-ELECTROLYSIS SYSTEM, HIGH-TEMPERATURE CO-ELECTROLYSIS PLANT AND METHOD FOR PRODUCEING SYNTHESEGAS

Description

[0001] The present invention relates to a high-temperature co-electrolysis system, a high-temperature co-electrolysis plant and a method for producing synthesis gas using an electrolysis system.

[0002] One way to reduce dependence on fossil fuels and lower CO2 emissions is to substitute crude oil with synthetic hydrocarbons produced from carbon dioxide (CO2) and water (H2O). Using electricity, high-temperature electrolysis (SOE, short for "solid oxide electrolysis") can produce synthesis gas containing hydrogen (H2) and carbon monoxide (CO). In a subsequent synthesis process, the synthetic hydrocarbons are obtained from this synthesis gas.

[0003] Electrolysis cell systems for high-temperature co-electrolysis are known, for example, from US 2014 / 272734 A1 and WL BECKER ET AL: "Production of Fischer-Tropsch liquid fuels from high temperature solid oxide co-electrolysis units", ENERGY, Vol. 47, No. 1, November 1, 2012 (2012-11-01), pages 99-115, XP055361383, AMSTERDAM, NL, ISSN: 0360-5442, DOI: 10.1016 / j.energy. 2012.08.047.

[0004] The object of the present invention is to increase the efficiency of the high-temperature electrolysis described above in a cost-effective and simple manner.

[0005] The foregoing problem is solved by a high-temperature co-electrolysis system with the features of claim 1, a high-temperature co-electrolysis plant with the features of claim 13, and a method with the features of claim 14. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawings. Features and details described in connection with the high-temperature co-electrolysis system according to the invention naturally also apply in connection with the high-temperature co-electrolysis plant and the method according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always refers, or can refer, to each other.

[0006] According to the invention, a high-temperature co-electrolysis system is provided. The high-temperature co-electrolysis system comprises an electrolysis cell stack with a cathode section, which includes a cathode supply section and a cathode discharge section, and an anode section, which includes an anode supply section and an anode discharge section. Furthermore, the high-temperature co-electrolysis system has an anode gas connection, fluidly coupled to the anode supply section by means of an anode supply connection, for supplying anode gas to the anode section. Additionally, the high-temperature co-electrolysis system has an anode discharge connection, fluidly coupled to the anode discharge section by means of an anode discharge connection, for removing anode gases generated by the electrolysis cell stack.Furthermore, the high-temperature co-electrolysis system features a cathode supply port, fluidly coupled to the cathode supply section via a cathode supply connection, for supplying cathode gas to the cathode section. Additionally, the high-temperature co-electrolysis system features a cathode discharge port, fluidly coupled to the cathode discharge section via a cathode discharge connection, for discharging synthesis gas generated by the electrolysis cell stack. The high-temperature co-electrolysis system also includes a residual gas supply port for providing residual gas that is separated from the synthesis gas generated by the electrolysis cell stack during a synthesis process for the production of synthetic hydrocarbons.The high-temperature co-electrolysis system further comprises two catalysts for the catalytic combustion of the residual gas, fluidly coupled to the residual gas supply connection via a residual gas supply connection and arranged in the anode discharge connection, wherein at least one of the two catalysts is designed as an oxidation catalyst. The high-temperature co-electrolysis system also comprises a second and a third heat exchanger, which are arranged in the anode discharge connection downstream of at least one of the two catalysts in the flow direction, wherein one of the second and third heat exchangers is thermally coupled to the anode supply connection, and the other of the second and third heat exchangers is thermally coupled to the cathode supply connection.

[0007] According to the invention, the efficiency of an electrolysis system is increased by utilizing residual gas from the synthesis process for the production of synthetic hydrocarbons for catalytic combustion within two catalysts of the high-temperature co-electrolysis system. The heat generated during the catalytic combustion is utilized within the high-temperature co-electrolysis system by means of at least one heat exchanger. This additional heat can be supplied at various locations, particularly specific feed connections such as the anode feed connection and / or cathode feed connection, within the high-temperature co-electrolysis system, thereby increasing the efficiency of the high-temperature co-electrolysis performed by the electrolysis cell stack to produce the synthetic gas, or in other words, synthesis gas.Compared to the use of a single catalyst and parallel heat exchangers, the use of two catalysts has the particular advantage that the second and third heat exchangers can be supplied with the same amount of heat at lower catalyst temperatures. Furthermore, higher air and / or reactant temperatures could be achieved at the same target outlet temperature. These and other advantages of the invention are explained and clarified in more detail below.

[0008] For the sake of simplicity, this description refers to an electrolysis cell stack. This means at least one electrolysis cell stack. Of course, it is possible to have multiple electrolysis cell stacks in the high-temperature co-electrolysis system, which can be interconnected in any way, e.g., in series or parallel. In this case, each cathode section and each anode section of each electrolysis cell stack is fluidically coupled to the connections mentioned herein, as described.

[0009] The electrolysis cell stack can be, in particular, a solid oxide electrolyzer cell stack. This means the electrolysis system can be a solid oxide electrolyzer cell system (SOEC system). The electrolysis cell stack in the electrolysis system operates in electrolysis mode, specifically in co-electrolysis mode, to achieve the electrolysis of water (H₂O) and carbon dioxide (CO₂). The electrolytes in the electrolysis cell stack then produce hydrogen gas (H₂), carbon monoxide (CO), and oxygen (O₂). It is advantageous if the electrolysis cell stack for generating the synthesis gas is connected to a power supply source that provides electricity from a renewable energy source.With such a power supply source, which is fed from renewable energy sources, the operation of high-temperature electrolysis can be designed in an ecologically sustainable way.

[0010] Within the scope of the invention, the term "high-temperature co-" is understood to include, in particular, a reversible electrolysis system. In a reversible electrolysis system, it is advantageously possible to switch between fuel cell operation and electrolysis operation.

[0011] For the electrolysis reaction described above, anode gas, in particular air, especially fresh air, or oxygen, is supplied to the anode section via the anode supply connection. Cathode gas, in particular carbon dioxide, is supplied to the cathode section via the cathode supply connection. The cathode supply connection can be connected to various carbon dioxide sources. For example, carbon dioxide can be extracted from the air, from biogas processes, from industrial exhaust gases, etc. Water can be supplied to the cathode supply section via a first auxiliary supply connection. This first auxiliary supply connection, which can be fluidically coupled to the cathode supply connection or the cathode supply section via a first auxiliary supply connection, can supply water, preferably in the form of steam, to the cathode supply section.Alternatively or additionally, the water in the electrolysis system can be vaporized to steam. The steam can be considered part of the cathode gas because it is supplied to the cathode feed section. Any protective gas supplied to the cathode feed section can also be considered part of the cathode gas because it is supplied to this section. The anode exhaust gases are discharged from the anode discharge section to the anode discharge port via the anode discharge port. These exhaust gases include, in particular, exhaust air or oxygen extracted from the electrolysis system, especially oxygen-enriched air, as well as catalyst exhaust gases downstream of the catalysts—that is, combustion products from the catalytic combustion of the residual gas mixed with the anode exhaust gas. From the anode discharge port, these gases can be released into the environment, for example.From the cathode discharge section, the generated cathode gas, which is synthesis gas containing primarily hydrogen gas and carbon monoxide, is fed to the cathode discharge port. This port can be connected to a synthesis plant via a suitable synthesis system to provide the synthetic gas for the production of synthetic hydrocarbons. Typically, not all of the synthesis gas can be converted during this synthesis process. Furthermore, in addition to the long-chain products, short-chain hydrocarbons are also produced during the synthesis process. The unreacted portion of the synthesis gas, together with the short-chain hydrocarbons, forms a gas mixture, which is partly recycled back into the synthesis plant and partly separated. This separated gas fraction is referred to here as residual gas.Surprisingly, it was discovered that this residual gas has a high calorific value and can advantageously be used to provide heat in high-temperature electrolysis, which in particular increases the efficiency of the electrolysis system in the manner according to the invention.

[0012] To distinguish between components or elements of the same type or species, such as heat exchangers, shut-off devices, partial paths, or bypass paths, the components or elements of the same type or species mentioned in this description are numbered and designated as first component, second component, third component (or elements), etc., for example, first heat exchanger, second heat exchanger, etc. This numbering serves solely to differentiate the components or elements of the same type or species mentioned herein and in no way constitutes a limitation of the scope of protection.For example, if a claim refers to a fourth component of a kind or type, this does not necessarily imply a first, second, and third component of that kind or type; unless the first, second, and third component of that kind or type are mentioned in a claim to which the claim in question refers.

[0013] The connections mentioned herein are fluid-carrying, in particular gas-carrying, connections. These connections can be established via various paths or lines, such as pipes or hoses, which are coupled to one another. Various flow-controlling devices, such as shut-off valves, can be arranged in these connections, as mentioned herein.

[0014] Insofar as this text refers to the arrangement of a heat exchanger in one connection and the thermal coupling of the heat exchanger with another connection, these characteristics are to be understood synonymously due to the function of the heat exchanger. The heat exchanger facilitates the exchange of heat between two flows in the respective connections, for example, in counterflow. In this respect, the heat exchanger is indeed located in each of the two connections, and the heat exchanger also thermally couples both connections.

[0015] Wherever the terms "control" or "monitoring" are used herein, particularly in connection with a shut-off valve, this refers to steering and / or regulating. Even if not explicitly stated, appropriate control electronics and monitoring devices beyond shut-off valves, such as flow meters, may be used for monitoring purposes.

[0016] The shut-off devices mentioned herein serve, at a minimum, to stop or allow the flow of the respective fluid, especially gas, within the connections. Depending on the type of shut-off device used, it is also possible to control the flow rate. These shut-off devices can be designed in a variety of ways, for example as valves, gate valves, stopcocks, or butterfly valves.

[0017] It is advantageous if the two catalysts are coupled via different, branching paths of the residual gas supply system. This allows the residual gas flow to each catalyst to be controlled. In other words, the amount of residual gas supplied to each catalyst can be controlled. Consequently, the heat transferred to the heat exchanger located downstream of each catalyst can also be controlled.

[0018] For this purpose, a fifth and / or sixth shut-off device can advantageously be arranged in at least one of the two partial paths. It is particularly advantageous to have such a shut-off device in each of the partial paths. For example, a butterfly valve can be used as a shut-off device. This allows for simple yet precise control of the residual gas flow to the catalysts and thus the amount of heat they generate through catalytic combustion.

[0019] It is also advantageous if each of the two partial paths is fluidically connected to the anode discharge connection upstream of a catalyst feed section of one of the two catalysts, in order to mix the residual gas and the anode exhaust gas into a residual gas-anode exhaust gas mixture. Consequently, the residual gas-anode exhaust gas mixture is introduced into the catalysts and catalytically combusted. This not only optimizes the catalytic combustion but also makes it possible to preheat the residual gas for catalytic combustion using the warm anode exhaust gas from the electrolysis cell stack.

[0020] It can also be advantageously provided that a first catalyst of the two catalysts is arranged downstream of a second catalyst of the two catalysts in the flow direction of the anode discharge connection. Consequently, the first catalyst provides a first catalyst stage, and the second catalyst provides a second catalyst stage. Particularly in conjunction with the aforementioned partial pathways, each catalyst stage can be individually controlled, for example, switched on or off, or the amount of residual gas supplied can be controlled, as required for optimal operation of the electrolysis system.Accordingly, one of the second and third heat exchangers can be arranged in the flow direction in the anode discharge connection behind both catalysts, and another of the second and third heat exchangers can be arranged in the flow direction in the anode discharge connection only behind the second catalyst.

[0021] According to the invention, one of the second and third heat exchangers is thermally coupled to the anode supply connection. This allows heat from the catalyst exhaust gases of one or both catalysts to be transferred to the anode supply connection, thus heating the anode gas arriving at the anode supply section in order to increase the efficiency of the high-temperature electrolysis.

[0022] Additionally, one of the second and third heat exchangers is thermally coupled to the cathode feed connection. This allows heat from the catalyst exhaust gases of one or both catalysts to be transferred to the cathode feed connection, thus heating the cathode gas arriving at the cathode feed section and increasing the efficiency of the high-temperature electrolysis. Preferably, one of the second and third heat exchangers is used for thermal coupling with the anode feed connection, and another for thermal coupling with the cathode feed connection.

[0023] Furthermore, it is advantageous if a fourth heat exchanger is arranged downstream of the second and third heat exchangers in the anode discharge connection and is thermally coupled to a first auxiliary feed connection. This auxiliary feed connection links the cathode feed connection or cathode feed section to a first auxiliary feed port for supplying water or steam to the cathode feed section. This allows the residual heat remaining in the catalyst exhaust gas after heat exchange in the second and third heat exchangers to be used in the anode discharge connection to heat the water or steam supplied at the first auxiliary feed port, thereby further increasing the efficiency of the electrolysis system.

[0024] Additionally or alternatively, and advantageously, a fifth heat exchanger can be provided in the flow direction in the anode discharge connection downstream of the second and third heat exchangers and is thermally coupled to the anode supply connection. This allows the residual heat in the exhaust gas remaining after the heat exchange in the second and third heat exchangers to be used in the anode discharge connection to heat the air transported in the anode supply connection, thereby further increasing the efficiency of the electrolysis system.

[0025] Furthermore, it is advantageous if a first heat exchanger is arranged in the anode supply line and thermally coupled to the anode discharge line upstream of the two catalysts. This allows, particularly in a first step, the heat from the catalyst exhaust gases to be used with the anode exhaust gas, especially the discharged air, from the anode discharge section to heat the anode gas, especially the supplied air. Besides heating the anode gas, this has the advantage that the anode exhaust gases from the anode section are cooled by the heat transfer, thereby reducing the auto-ignition temperature of the residual gas-anode exhaust gas mixture, which is generated by mixing the residual gas and the anode exhaust gas downstream of the first heat exchanger. This is because the anode exhaust gas is very oxygen-rich, with approximately...30% oxygen, since oxygen diffuses from the cathode section to the anode section in the electrolysis cell stack. Lowering the temperature below the auto-ignition temperature is advantageous because it prevents high thermal stress on the components in the electrolysis system and ensures controlled combustion via the subsequent catalyst.

[0026] It is advantageous if a third bypass path connects the anode supply connection upstream of the first heat exchanger with the anode supply connection downstream of the first heat exchanger, wherein a third shut-off device is arranged in the third bypass path bypassing the first heat exchanger, and / or a fourth shut-off device is arranged in the anode supply connection downstream of a branch from the anode supply connection to the third bypass path and upstream of the first heat exchanger. This allows the supplied air in the anode supply connection to easily bypass the first heat exchanger. Furthermore, this enables simple control of the temperature of the anode gas and the anode exhaust gas in the respective anode connection.

[0027] Advantageously, a first heating device can be arranged in the third bypass path. This first heating device can be, in particular, an electric heater. This allows the temperature of the supplied anode gas to be increased even further in order to operate the electrolysis cell stack at its optimal operating point.

[0028] Furthermore, the anode discharge connection is advantageously connected to the anode supply connection upstream of at least one of the two catalysts by means of a first and / or a second bypass path. In particular, such bypass paths, namely a first bypass path and a second bypass path, can be provided upstream of each of the two catalysts, and these bypass paths are connected to the anode supply connection. This allows, in addition to the mixing that already occurs upstream of the catalysts, in which the oxygen-rich exhaust air of the anode gas from the anode discharge section is mixed with the residual gas, additional cool air for catalytic combustion to be introduced into the catalyst, thus also cooling the catalysts. Advantageously, a shut-off device is arranged in the bypass path.It is particularly advantageous to have a first shut-off valve in the first bypass path and a second shut-off valve in the second bypass path. This allows for control of the amount of additional air supplied.

[0029] It is further stipulated that at least one of the two catalysts is designed as an oxidation catalyst. In particular, both catalysts can be designed as oxidation catalysts. An oxidation catalyst can oxidize pollutants such as carbon monoxide and hydrocarbons, but it cannot reduce nitrogen oxides. With the help of an oxidation catalyst, not only can the energy contained in the residual gas be utilized in the form of heat, but the hydrogen still present in the exhaust gas is also converted.

[0030] Finally, it is advantageous if the electrolysis system also has a first auxiliary feed port for supplying heated steam, which is heated during cooling in the synthesis process to produce synthetic hydrocarbons from the synthesis gas generated by the electrolysis cell stack. Accordingly, for efficiency optimization of the electrolysis system, not only the residual gas from the synthesis process but also the heated steam generated during cooling in the synthesis process is utilized, thereby achieving a dual and synergistic efficiency optimization of the high-temperature electrolysis.

[0031] The present invention also relates to a high-temperature co-electrolysis plant comprising a high-temperature co-electrolysis system according to the invention and a synthesis system comprising a synthesis unit. The cathode discharge connection is fluidically coupled to the synthesis unit via a synthesis gas supply connection. The synthesis unit is also equipped for the synthesis of synthetic hydrocarbons produced from the synthesis gas generated by the electrolysis cell stack and supplied via the synthesis gas supply connection. Finally, the synthesis unit is fluidly coupled to the residual gas supply connection via a residual gas discharge connection for the provision of residual gas.

[0032] Within the scope of the invention, the high-temperature co-electrolysis system is to be understood in particular as a complete system, which is preferably designed as a so-called "power-to-liquid" or PtL system.

[0033] Thus, a high-temperature co-electrolysis system according to the invention offers the same advantages as have been explained in detail with reference to the high-temperature co-electrolysis system according to the invention.

[0034] Also part of the present invention is a method for producing synthesis gas using a high-temperature co-electrolysis system, in particular the high-temperature co-electrolysis system according to the invention, and furthermore, in particular, using the high-temperature co-electrolysis plant according to the invention, comprising the steps of: Feeding residual gas separated from a synthesis process in which synthesis gas is converted into hydrocarbons to two catalysts of a high-temperature co-electrolysis system, wherein at least one of the two catalysts is designed as an oxidation catalyst, catalytic combustion of the residual gas using the two catalysts of the high-temperature co-electrolysis system, transferring heat from a catalyst exhaust stream of the catalytic combustion of the two catalysts to an anode gas and a cathode gas via two heat exchangers, feeding the anode gas, the cathode gas and an electric current to an electrolysis cell stack of the high-temperature co-electrolysis system, and generating the synthesis gas using the electrolysis cell stack from the supplied anode gas, cathode gas and electric current.

[0035] Thus, a method according to the invention offers the same advantages as those that have been explained in detail with reference to the high-temperature co-electrolysis system according to the invention.

[0036] In particular, the high-temperature co-electrolysis system and / or the high-temperature co-electrolysis plant according to the invention can be set up or configured to carry out the process according to the invention.

[0037] The term "anode gas" refers to the gas supplied to the anode section, in particular air or oxygen. This excludes the anode exhaust, i.e., the exhaust gas discharged from the anode section, in particular air and / or oxygen. The term "cathode gas" refers to the gas supplied to the cathode section, in particular carbon dioxide, water vapor, and / or a protective gas. This excludes the cathode exhaust, i.e., the synthetic gas discharged from the cathode section.

[0038] It has proven advantageous to divide the residual gas flow into two paths and supply each of the two catalysts via one of these paths. This allows for the control of residual gas flows to the catalysts, as mentioned above, and thus the control of heat transfer between the anode and cathode supply lines. In particular, it is advantageous to ensure that essentially the same amount of heat is transferred to both heat exchangers, and therefore to both the anode and cathode supply lines, by controlling the residual gas flow in the two paths accordingly.

[0039] For this purpose, it is advantageous if the catalyst exhaust gas flow in the two sub-paths is controlled by means of a shut-off device in each of the two sub-paths behind the respective heat exchanger of the respective sub-path.

[0040] It is also advantageous if the exhaust gas stream from one of the two catalysts is fed to the other catalyst via the anode return connection. This allows the heat from the exhaust gas stream of one catalyst to be used for the catalytic combustion of the other catalyst, thus maintaining high efficiency.

[0041] Finally, it is preferred that the catalyst exhaust streams flow through a fourth heat exchanger for further heat transfer to warm water or steam supplied to the electrolysis system and / or through a fifth heat exchanger to warm the anode gas. This makes it possible to utilize any remaining residual heat in the catalyst exhaust streams to further increase the efficiency of the electrolysis system.

[0042] It is also advantageous if the residual gas is mixed with the anode exhaust gas from the electrolysis cell stack in the direction of flow upstream of the catalysts to form a residual gas-anode exhaust gas mixture. The oxygen-rich air in the anode exhaust gas can thus raise the temperature of the residual gas-anode exhaust gas mixture and be used for controlled catalytic combustion.

[0043] It is advantageous if the anode exhaust gas transfers heat to the supplied anode gas via a first heat exchanger before being mixed with the residual gas. This allows the supplied anode gas to be heated by the air and the anode exhaust gas to be cooled by the air, particularly below the auto-ignition temperature of the residual gas-anode exhaust gas mixture.

[0044] Furthermore, it is advantageous to add anode gas to the residual gas-anode exhaust mixture. This can be achieved through the aforementioned bypass paths, particularly the first and second bypass paths. In this way, the amount of fresh air containing anode gas in the residual gas-anode exhaust mixture can be further increased.

[0045] It has proven advantageous if the residual gas-anode exhaust gas mixture has a temperature in the range of 300 to 550 °C, particularly in the range of 400 to 500 °C. This refers to the temperature at the catalyst feed sections of the catalysts. The highest efficiency increase in synthesis gas production has been observed in this temperature range.

[0046] It is advantageous if the catalyst exhaust gases from catalytic combustion have a temperature in the range of 800 to 1,000 °C, particularly in the range of 850 to 950 °C. This refers to the temperature at the catalyst discharge sections. The highest efficiency increase in synthesis gas production has been observed in this temperature range.

[0047] Advantageously, the generated synthesis gas is fed into the synthesis process, from which the residual gas is separated and fed to the two catalysts.

[0048] It is also advantageous if the synthesis process is a Fischer-Tropsch process. The coupling of high-temperature co-electrolysis and Fischer-Tropsch synthesis (FTS) has proven to be a particularly promising approach for the production of various hydrocarbons. In FTS, synthesis gas generated from high-temperature co-electrolysis is converted into hydrocarbon molecules with different chain lengths at comparatively moderate temperatures, particularly in the temperature range of 200 to 300 °C, and elevated pressures, particularly in the pressure range of 10 to 30 bar, using a catalyst, especially cobalt- or iron-based. The FTS process is highly exothermic. To maintain the temperature within the specified range, cooling can be achieved along the length of a reactor in the synthesis plant. This cooling can be accomplished by water evaporation at the specified pressure level.The steam can subsequently be used for further process steps and, as mentioned previously, for the high-temperature electrolysis itself by adding the steam to the cathode gas. The hydrocarbon chain length distribution generated in FTS is described by a chain growth probability (high chain growth probability results in large molecules and thus a shift towards liquid fuels). However, the synthesis gas is not completely converted. Furthermore, depending on the chain growth probability, short-chain molecules are formed that cannot be used as liquid fuel. The unreacted synthesis gas and the resulting short-chain hydrocarbons can be separated as residual gas in the product processing stage. While some of the residual gas can be recirculated into the FTS, some must be discharged. The discharged portion of the residual gas, in particular, is used in the process according to the invention.

[0049] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments are described in detail with reference to the drawings. The drawings schematically show: Fig. 1 shows a first embodiment of a high-temperature co-electrolysis plant according to the invention, Fig. 2 shows a second embodiment of a high-temperature co-electrolysis plant according to the invention, Fig. 3 shows a third embodiment of a high-temperature co-electrolysis plant according to the invention, and Fig. 4 shows an embodiment of a method according to the invention.

[0050] Identical or functionally equivalent elements are in the Figures 1 to 4 each designated with the same reference symbol.

[0051] Figure 1Figure 1 schematically shows a high-temperature co-electrolysis plant 30 comprising a high-temperature co-electrolysis system 10 with an electrolysis cell stack 100 and a synthesis system 20 with a synthesis plant 900. The high-temperature co-electrolysis system 10 and the synthesis system 20 are fluidically coupled, as will be explained in more detail later.

[0052] For example, in the Fig. 1Only one electrolysis cell stack 100 is shown. However, it is possible to provide several electrolysis cell stacks 100. The electrolysis cell stack 100 has a cathode section 110 with a cathode feed section 112 and a cathode discharge section 114. Furthermore, the electrolysis cell stack 100 has an anode section 120 with an anode feed section 122 and an anode discharge section 124. A power supply 130, which provides electricity from renewable energy sources, is connected to the electrolysis cell stack 100. The electrolysis cell stack 100 is designed here as a solid oxide electrolysis cell stack and is used in electrolysis mode for high-temperature co-electrolysis.

[0053] Anode gas in the form of fresh air is supplied to the high-temperature co-electrolysis system 10 via an anode gas connection 202. The anode gas is supplied to the electrolysis cell stack 100 for electrolysis via an anode supply connection 200, which is fluidly coupled to the anode gas connection 202 and the anode supply section 122. A filter device 204, in particular an air filter, for air filtration and a blower 206 for transporting the anode gas are arranged in the anode supply connection 200.

[0054] In the anode supply connection 200, a first heat exchanger 224 is arranged downstream of the filter unit 204 and the blower 206, in the direction of anode gas flow from the anode gas connection 202 to the anode supply section 122. The first heat exchanger 224 is used for heat exchange with warm anode exhaust gas, particularly in the form of exhaust air discharged from the electrolysis cell stack 100 by the anode section 120. For this purpose, the first heat exchanger 224 is thermally coupled to an anode discharge connection 300 upstream of a second catalyst 418 in the form of an oxidation catalyst. The anode discharge connection 300 fluidically connects the anode discharge section 124 to an anode discharge port 308.

[0055] The second catalyst 418 is arranged in the anode discharge connection 300 downstream of the first heat exchanger 224 in the direction of anode exhaust gas flow and is fluidically coupled to a residual gas connection 402 via a residual gas supply connection 400. The residual gas connection 402 receives residual gas from the synthesis unit 900, as will be described in more detail later. The residual gas supplied to a second catalyst feed section 420 of the second catalyst 418, which is mixed with the anode exhaust gas in the anode discharge connection 300 at a junction between the residual gas supply connection 400 and the anode discharge connection 300 to form a residual gas-anode exhaust gas mixture, is catalytically combusted by the second catalyst 418. Hot catalyst exhaust gases with a temperature in the range of 800 to 1000 °C, especially around 950 °C, exit from the second catalyst discharge section 422.

[0056] A second bypass path 212 with a second shut-off device 214 arranged therein connects the anode supply connection 200 in the flow direction of the anode gas in front of the first heat exchanger 224 with the anode discharge connection 300 in front of the second catalyst supply section 420 and thus allows the air content of the residual gas-anode exhaust gas mixture to be further increased before entering the second catalyst 418 and the residual gas-anode exhaust gas mixture to be further cooled.

[0057] In addition, a third bypass path 216 with a third shut-off device 218 is provided, which connects the anode supply connection 200 in the flow direction of the anode gas upstream of the first heat exchanger 224 with the anode supply connection 200 in the flow direction of the anode gas downstream of the first heat exchanger 224, thereby making it possible to control the temperature of the residual gas-anode exhaust gas mixture upstream of the second catalyst 418 by regulating the amount of anode gas flowing through the first heat exchanger 224. Furthermore, a fourth shut-off device 222 is arranged upstream of the second heat exchanger 302 and downstream of the third bypass path 216.

[0058] The hot catalyst exhaust gases from the second catalyst 418 flow from the second catalyst discharge section 422 in the anode discharge connection 300 through a second heat exchanger 302, which is thermally coupled to the anode supply connection 200. This allows the heat from the catalyst exhaust gas of the second catalyst 418 to be transferred to the anode gas upstream of the anode supply section 122.

[0059] In addition to the second catalyst 418, the high-temperature co-electrolysis system 10 also includes a further catalyst 408, referred to herein as the first. The first catalyst 408 is located in the anode discharge connection 300 downstream of the second catalyst 418, i.e., downstream of the second heat exchanger 302 and in the catalyst exhaust stream of the second catalyst 418. The residual gas supply connection 400 is divided into two separate sub-paths 404 and 414, namely a first sub-path 404 and a second sub-path 414. A fifth shut-off device 406 is located in the first sub-path 404. A sixth shut-off device 416 is located in the second sub-path 414. In this respect, the residual gas quantity supplied to each of the two catalysts 408, 418 can be controlled by means of the shut-off devices 406, 416, and thus the amount of heat released by the catalyst exhaust gases through catalytic combustion.As explained above, a mixing of residual gas and anode exhaust gas occurs at the aforementioned junction before the second catalyst feed section 420 of the second catalyst 418. Similarly, a mixing of residual gas and catalyst exhaust gases, which are also referred to here as anode exhaust gas because they flow in the anode exhaust connection 300, occurs at a junction before the first catalyst feed section 410 of the first catalyst at a junction where the anode discharge section 300 and the first partial path 404 meet. This mixing is likewise referred to here as a residual gas-anode exhaust gas mixture.

[0060] Downstream of the first catalyst 408 and its first catalyst discharge section 412, a third heat exchanger 304 is located in the anode discharge connection 300. The third heat exchanger 304 is thermally coupled to a cathode supply connection 500. The cathode supply connection 500 fluidically connects a cathode supply port 502 to the cathode supply section 112. Cathode gas, in particular carbon dioxide, is supplied from the cathode supply port 502 to the cathode supply section 112 in the cathode supply connection 500. Downstream of the cathode section 110, a seventh shut-off device 504 and an ejector 506 are arranged in the cathode supply connection 500. Furthermore, a second heating device 508, in the form of an electric heater, is arranged behind the ejector 506 in the direction of flow of the anode gas.The third heat exchanger 304 allows the cathode gas to be heated with the heat from the catalyst exhaust gas of one or both catalysts 408, 418.

[0061] A first bypass path 208 with a first shut-off device 210 arranged therein connects the anode supply connection 200 in the flow direction of the anode gas upstream of the first heat exchanger 224, and in particular upstream of the branch to the second bypass path 212, with the anode discharge connection 300 upstream of the first catalyst supply section 410 and thus allows the air content of the residual gas-anode exhaust gas mixture to be increased before entering the first catalyst 408 and the residual gas-anode exhaust gas mixture to be cooled.

[0062] With the arrangement of catalysts 408, 418 in the high-temperature co-electrolysis system 10 described above, it is thus possible to operate only one or both catalysts 408, 418 together, the latter being preferred. In this way, the oxygen-rich exhaust air in the anode exhaust can be mixed with a first quantity of the residual gas, which can be controlled by means of the sixth shut-off device 416, for controlled catalytic combustion via the second catalyst 418, which in this respect functions as the first oxidation catalyst stage, to supply the temperature to the second heat exchanger 302, which acts as an air superheater for the air in the anode gas.The oxygen-rich catalyst exhaust gas from the second catalyst 418 can again be mixed with a second quantity of the residual gas, which can be controlled by means of the fifth shut-off device 406, for controlled catalytic combustion via the first catalyst 408, which in this respect functions as a second oxidation catalyst stage, to provide temperature at the third heat exchanger 304, which functions as a reactant superheater for the cathode gas.

[0063] The two oxidation catalyst stages ensure the same heat exchange at lower oxidation catalyst target temperatures (meaning the total mass flow through both heat exchangers 302, 304 and the same enthalpy at lower temperatures), or vice versa, as in a single-stage system with the two heat exchangers 302, 304 arranged in parallel. Furthermore, it is advantageous that higher air and reactant temperatures can be achieved at the same oxidation catalyst target temperature.

[0064] The present interconnection of catalysts 408, 418 in the high-temperature co-electrolysis system 10 can be used as an alternative to the one described in Fig. 1The arrangement shown can also be such that the third heat exchanger 304 is arranged in the catalyst exhaust stream of the second catalyst 418 and the second heat exchanger 302 is arranged in the catalyst exhaust stream of the first catalyst 408. It should be noted again that the designation of components or elements of the same type or kind serves only to distinguish them from one another and does not follow any technically necessary sequence or the like.

[0065] In the direction of flow of the catalyst exhaust gas behind the second heat exchanger 302, in the embodiment of the Fig. 1In the anode discharge connection 300, a fourth heat exchanger 306 is located. This fourth heat exchanger 306 is thermally coupled to a first auxiliary supply connection 700, which fluidically connects a first auxiliary supply port 702 to the cathode supply connection 500. Water or steam is supplied from the first auxiliary supply port 702 for the high-temperature co-electrolysis. This water or steam is heated by the fourth heat exchanger 306 and flows to the cathode supply connection 500.

[0066] Cathode exhaust gas, in the form of synthesis gas containing hydrogen and carbon monoxide, produced by high-temperature co-electrolysis, is discharged to the synthesis system 20 via a cathode discharge connection 600, which fluidically connects the cathode discharge section 114 to a cathode discharge port 612. Two heat exchangers 608 and 610, namely a sixth heat exchanger 608 and a seventh heat exchanger 610, are thermally arranged in the cathode discharge connection 600 and thermally coupled to the cathode supply connection 500 to transfer heat from the synthesis gas to the cathode gas, thereby increasing the efficiency of the high-temperature co-electrolysis system 10.

[0067] A fourth bypass path 602 leads from the cathode discharge section 600 to the ejector 506. In the fourth bypass path 602, a nozzle 604, in particular a Venturi nozzle, and an eighth shut-off device 606, in particular a valve, are arranged.

[0068] A second additional supply connection 800 fluidically connects a second additional supply port 802 for supplying a protective gas to the cathode supply connection 500 in the flow direction of the cathode supply connection 500 upstream of the seventh shut-off device 504.

[0069] The electrolysis cell stack 100, supplied with anode gas comprising air and cathode gas comprising carbon dioxide, water vapor, and protective gas in the manner described above, generates cathode exhaust gas in the form of synthesis gas comprising hydrogen and carbon monoxide, and anode exhaust gas comprising exhaust air, in electrolysis mode by high-temperature co-electrolysis. The anode exhaust gas is catalytically combusted by the two catalysts 408 and 418 together with residual gas, so that catalyst exhaust gases are separated from the high-temperature co-electrolysis system 10 at the anode discharge port 308.

[0070] The synthesis gas is supplied to synthesis plant 900 of synthesis system 20 via a synthesis gas supply connection 906, which fluidically connects a synthesis feed section 902 of synthesis plant 900 to the cathode discharge port 612. In a reactor located there (not explicitly shown), it undergoes a synthesis process, in particular a Fischer-Tropsch synthesis process, and is converted into synthetic hydrocarbons. The hydrocarbons are discharged via a hydrocarbon discharge connection 908, which is fluidically connected to a synthesis discharge section 904. However, synthesis gas not converted during the synthesis process and short-chain hydrocarbons remain. Some of these can be returned to the synthesis process, while some can be discharged as residual gases via a residual gas discharge connection 910 to the residual gas supply port 402, which are fluidically coupled to each other.

[0071] Figure 2 shows a modification of the embodiment of the electrolysis system 30 of the Fig. 1 . And that was in the Fig. 2 The fourth heat exchanger 306 was omitted. Instead, a fifth heat exchanger 310 was installed in the anode discharge connection 300 downstream of the two heat exchangers 302 and 304. This fifth heat exchanger is thermally coupled to the anode supply connection 200, specifically downstream of the blower 206 and upstream of the first heat exchanger 224 in the direction of anode gas flow. This allows the residual heat in the anode exhaust or catalyst exhaust to be used as an alternative for the anode gas. However, it is also possible to provide both the fourth heat exchanger 306 and the fifth heat exchanger 310, either in series or in parallel with appropriate shut-off devices and bypass paths.

[0072] Furthermore, any configuration of the heat exchangers 224, 302, 304, 306, 310, 608, 610 shown is possible, which means that these heat exchangers can each be used individually or in any selection thereof in the high-temperature co-electrolysis system 10, so that it is not necessary to equip the high-temperature co-electrolysis system 10 with all heat exchangers 224, 302, 304, 306, 310, 608, 610.

[0073] Figure 3 shows a variation of the electrolysis system 30 of the embodiment of the Fig. 1, in which changes are provided for in the synthesis system 20. A cooling device in the synthesis plant 900 is shown with dashed lines, which in particular cools a corresponding reactor in the synthesis plant 900. Steam is used to cool the strongly exothermic reaction of the synthesis process. The heated steam is advantageously supplied to the first auxiliary feed port 702 by means of a corresponding third auxiliary feed connection, which is fluidically connected to the first auxiliary feed port 702.

[0074] Figure 4 This is already shown in relation to the Figs. 1 to 3Method 1000 for producing synthesis gas using the high-temperature co-electrolysis system 10 is explained using the high-temperature co-electrolysis plant 30 as an example. Method 1000 is shown purely schematically with reference to its process steps 1002, 1004, 1006, 1008, 1010, whereby further process steps, not explicitly shown, may be added.

[0075] In a first process step 1002 of process 1000, residual gas is separated from the synthesis process taking place in the synthesis plant 900, in which the synthesis gas from the cathode discharge port 612 is converted into hydrocarbons. The residual gas is supplied to the residual gas supply port 402 via the residual gas discharge connection 910 and thus supplied to the two catalysts 408, 418 via the partial paths 404, 414 of the residual gas supply connection 400 of the high-temperature co-electrolysis system 10.

[0076] In the second process step 1004 of process 1000, the residual gas is catalytically combusted by means of the two catalysts 408 and 418. Corresponding catalyst exhaust gases emerge from their catalyst discharge sections 412 and 422. The catalyst exhaust gases can have a temperature in the range of 800 to 1,000 °C. The residual gas upstream of the second catalyst 418 can, as in the Figs. 1 to 3 As can be seen, the gas is first mixed with the anode exhaust, i.e., the exhaust air from the electrolysis cell stack 100, and optionally also with the anode gas, i.e., fresh air, via the second bypass path 212, so that a residual gas-anode exhaust mixture enters the second catalyst feed section 420. The residual gas can also be mixed before the first catalyst 408, as shown in the Figs. 1 to 3As can be seen, the exhaust gas is first mixed with the anode exhaust gas, i.e., the oxygen-rich catalyst exhaust gas from the second catalyst 418, and optionally also with the anode gas, i.e., fresh air, via the first bypass path 208, so that a residual gas-anode exhaust gas mixture enters the first catalyst feed section 410. The residual gas-anode exhaust gas mixture can have a temperature in the range of 300 to 550 °C.

[0077] In the third process step 1006 of process 1000, heat from the catalyst exhaust gas streams of the two catalysts 408, 418 of the catalytic combustion is transferred at least by means of the heat exchangers 302, 304 to the anode gas in the anode supply connection 200 and the cathode gas in the cathode supply connection 500, and advantageously also by means of the fourth heat exchanger 306 and / or the fifth heat exchanger 310.

[0078] In a fourth process step 1008 of process 1000, the heated anode and cathode gases are fed to the electrolysis cell stack 100 of the high-temperature co-electrolysis system 10 with the addition of an electric current. Finally, in the fifth process step 1010, the synthesis gas can be produced from the supplied anode gas, cathode gas, and electric current using the electrolysis cell stack 100.

[0079] The process steps 1002 to 1010 of process 1000 are carried out continuously, as indicated by the arrow from process step 1010 to process step 1002.

[0080] The preceding explanations of the embodiments describe the present invention exclusively by way of examples. Reference symbol list

[0081] 10 High-temperature co-electrolysis system 20 Synthesis system 30 High-temperature co-electrolysis plant 100 Electrolysis cell stack 110 Cathode section 112 Cathode feed section 114 Cathode discharge section 120 Anode section 122 Anode feed section 124 Anode discharge section 130 Power supply source 200 Anode feed connection 202 Anode feed connection 204 Filter unit 206 Blower 208 First bypass path 210 First shut-off valve 212 Second bypass path 214 Second shut-off valve 216 Third bypass path 218 Third shut-off valve 220 First heating unit 222 Fourth shut-off valve 224 First heat exchanger 300 Anode discharge connection 302 Second heat exchanger 304 Third Heat exchanger 306 fourth heat exchanger 308 anode discharge connection 310 fifth heat exchanger 400 residual gas supply connection 402 residual gas supply connection 404 first partial path 406 fifth shut-off device 408 first catalyst 410 first catalyst supply section 412 second catalyst supply section 414 second partial path 416 sixth shut-off device 418 second catalyst420 Second catalyst feed section 422 Second catalyst discharge section 500 Cathode feed connection 502 Cathode feed connection 504 Seventh shut-off valve 506 Ejector 508 Second heating device 600 Cathode discharge connection 602 Fourth bypass path 604 Nozzle 606 Eighth shut-off valve 608 Sixth heat exchanger 610 Seventh heat exchanger 612 Cathode discharge connection 700 First auxiliary feed connection 702 First auxiliary feed connection 800 Second auxiliary feed connection 802 Second auxiliary feed connection 900 Synthesis plant 902 Synthesis feed section 904 Synthesis discharge section 906 Synthesis gas feed connection 908 Hydrocarbon discharge connection 910 Residual gas discharge connection 1000 Process 1002 first process step 1004 second process step 1006 third process step 1008 fourth process step 1010 fifth process step

Claims

1. A high-temperature co-electrolysis system (10), comprising: - an electrolysis cell stack (100) with a cathode section (110) having a cathode supply section (112) and a cathode discharge section (114), and an anode section (120) having an anode supply section (122) and an anode discharge section (124), - an anode gas connection (202) fluidly coupled to the anode supply section (112) by means of an anode supply connection (200) for supplying anode gas to the anode section (120), - an anode discharge connection (308) fluidly coupled to the anode discharge section (124) by means of an anode discharge connection (300) for discharging the anode gas flowing through the electrolysis cell stack (100) generated anode exhaust gases, - a cathode supply connection (502) fluidly coupled to the cathode supply section (112) by means of a cathode supply connection (500) for supplying cathode gas to the cathode section (110), and - a cathode discharge connection (612) fluidly coupled to the cathode discharge section (114) by means of a cathode discharge connection (600) for discharging synthesis gas generated by the electrolysis cell stack (100), characterized in that the high-temperature co-electrolysis system (10) further comprises: - a residual gas supply connection (402) for providing residual gas which is separated from the synthesis gas generated by the electrolysis cell stack (100) during a synthesis process for producing synthetic hydrocarbons, - two catalysts (408, 418) fluidically coupled to the residual gas supply connection (402) by means of a residual gas supply connection (400) and arranged in the anode discharge connection (300) for the catalytic combustion of the residual gas, wherein at least one of the two catalysts (404) is designed as an oxidation catalyst, and - a second heat exchanger (302) and a third heat exchanger (304) arranged in the anode discharge connection (300) downstream of at least one of the two catalysts (408, 418) in the flow direction, wherein one of the second and third heat exchangers (302, 304) is thermally coupled to the anode supply connection (200) and wherein the other of the second and third heat exchangers (302, 304) is thermally coupled to the cathode supply connection (500) is coupled2. High-temperature co-electrolysis system (10) according to claim 1, characterized in that the two catalysts (408, 418) are coupled to different, dividing sub-paths (404, 414) of the residual gas supply connection (400).

3. High-temperature co-electrolysis system (10) according to claim 2, characterized in that a fifth and / or a sixth shut-off device (406, 416) is arranged in at least one of the two partial paths (404, 414).

4. High-temperature co-electrolysis system (10) according to claim 2 or 3, characterized in that each of the two partial paths (404, 414) is fluidly connected to the anode discharge connection (300) upstream of a catalyst feed section (410, 420) of one of the two catalysts (408, 418) in order to mix the residual gas and the anode exhaust gas to form a residual gas-anode exhaust gas mixture.

5. High-temperature co-electrolysis system (10) according to one of the preceding claims, characterized in that a first catalyst (408) of the two catalysts (408, 418) is arranged downstream of a second catalyst (418) of the two catalysts (408, 418) in the flow direction of the anode discharge connection (300).

6. High-temperature co-electrolysis system (10) according to one of the preceding claims, characterized in that a fourth heat exchanger (306) is arranged downstream of the second and third heat exchangers (302, 304) in the anode discharge connection (300) and is thermally coupled to a first auxiliary supply connection (700) which connects the cathode supply connection (500) or the cathode supply section (112) to a first auxiliary supply connection (702) for supplying water or steam to the cathode supply section (112).

7. High-temperature co-electrolysis system (10) according to one of the preceding claims, characterized in that a fifth heat exchanger (310) is arranged in the flow direction in the anode discharge connection (300) downstream of the second and third heat exchangers (302, 304) and is thermally coupled to the anode supply connection (200).

8. High-temperature co-electrolysis system (10) according to one of the preceding claims, characterized in that a first heat exchanger (224) is arranged in the anode supply connection (200) and is thermally coupled to the anode discharge connection (300) upstream of the two catalysts (408, 418) in the flow direction.

9. High-temperature co-electrolysis system (10) according to claim 8, characterized in that a third bypass path (216) connects the anode supply connection (200) upstream of the first heat exchanger (224) with the anode supply connection (200) downstream of the first heat exchanger (224), wherein a third shut-off device (218) is arranged in the third bypass path (216) bypassing the first heat exchanger (224), and / or a fourth shut-off device (222) is arranged in the anode supply connection (200) downstream of a branch from the anode supply connection (200) to the third bypass path (216) and upstream of the first heat exchanger (224).

10. High-temperature co-electrolysis system (10) according to claim 9, characterized in that a first heating device (220) is arranged in the third bypass path (216).

11. High-temperature co-electrolysis system (10) according to one of the preceding claims, characterized in that the anode discharge connection (300) is connected to the anode supply connection (200) upstream of at least one of the two catalysts (408, 318) by means of a first and / or a second bypass path (208, 212).

12. High-temperature co-electrolysis system (10) according to one of the preceding claims, characterized in that the high-temperature co-electrolysis system (10) further comprises a first auxiliary supply port (702) for providing heated steam, which is heated during cooling in the synthesis for producing synthetic hydrocarbons from the synthesis gas generated by the electrolysis cell stack (100).

13. A high-temperature co-electrolysis plant (30) comprising a high-temperature co-electrolysis system (10) according to one of the preceding claims and a synthesis system (20) comprising a synthesis plant (900), wherein: - the cathode discharge connection (612) is fluidly coupled to the synthesis plant (900) by means of a synthesis gas supply connection (906), - the synthesis plant (900) is configured to synthesize the synthetic hydrocarbons produced from the synthesis gas generated by the electrolysis cell stack (100) and supplied by means of the synthesis gas supply connection (906), and - the synthesis plant (900) is fluidly coupled to the residual gas supply connection (402) by means of a residual gas discharge connection (910) for providing residual gas.

14. A method (1000) for generating synthesis gas using a high-temperature co-electrolysis system (10), comprising the steps of: - feeding residual gas separated from a synthesis process in which synthesis gas is converted into hydrocarbons to two catalysts (408, 418) of a high-temperature co-electrolysis system (10), wherein at least one of the two catalysts (404) is designed as an oxidation catalyst, - catalytically combusting the residual gas using the two catalysts (408, 418) of the high-temperature co-electrolysis system (10), - transferring heat from catalyst exhaust streams from the catalytic combustion of the two catalysts (408, 418) to an anode gas and a cathode gas, respectively, using two heat exchangers (302, 304), - feeding the anode gas, cathode gas, and electric current to an electrolysis cell stack (100) of the high-temperature co-electrolysis system (10), and - generating the synthesis gas by means of the electrolysis cell stack (100) from the supplied anode gas, cathode gas, and electric current.

15. Method (1000) according to claim 14, characterized in that the residual gas stream is divided into two partial paths (404, 414) and residual gas is supplied to one of the two catalysts (408, 418) by means of one of the two partial paths (404, 414).