Electrolysis system for the production of a synthesis gas
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- AVL LIST GMBH
- Filing Date
- 2024-08-21
- Publication Date
- 2026-04-22
Smart Images
Figure AT2024060320_27022025_PF_FP_ABST
Abstract
Description
[0001] Electrolysis system for generating a synthesis gas
[0002] The present invention relates to an electrolysis system, an electrolysis plant and a method for producing synthesis gas by means of an electrolysis system.
[0003] One way to reduce dependence on fossil fuels and CO2 emissions is to replace crude oil with synthetic hydrocarbons produced from carbon dioxide (CO2) and water (H2O). By applying electrical current, high-temperature electrolysis (SOE for "Solid Oxide Electrolysis") can produce a synthesis gas containing hydrogen (H2) and carbon monoxide (CO). In a subsequent synthesis process, the synthetic hydrocarbons are obtained from the synthesis gas.
[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 above object is achieved by an electrolysis system having the features of claim 1, an electrolysis plant having the features of claim 9, and a method having the features of claim 12. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the electrolysis system according to the invention naturally also apply in connection with the electrolysis plant according to the invention and the method according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made to each other.
[0006] According to the invention, an electrolysis system is provided. The electrolysis system comprises an electrolysis cell stack with a cathode section, which has a cathode supply section and a cathode discharge section, and an anode section, which has an anode supply section and an anode discharge section. Furthermore, the electrolysis system comprises 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. Furthermore, the electrolysis system comprises an anode discharge connection, fluidly coupled to the anode discharge section by means of an anode discharge connection, for discharging anode exhaust gases generated by the electrolysis cell stack.Furthermore, the electrolysis system has a cathode supply connection, fluidly coupled to the cathode supply section by means of a cathode supply connection, for supplying cathode gas to the cathode section. Furthermore, the electrolysis system has a cathode discharge connection, fluidly coupled to the cathode discharge section by means of a cathode discharge connection, for discharging synthesis gas generated by the electrolysis cell stack. The electrolysis system also has a recycle gas connection for providing recycle gas, which is produced as a by-product in a subsequent synthesis process for producing synthetic hydrocarbons from the synthesis gas generated by the electrolysis cell stack, wherein the recycle gas connection is fluidly connected to the cathode supply connection.
[0007] For the sake of simplicity, the present description refers to an electrolysis cell stack. This means at least one electrolysis cell stack. Of course, it is possible for several electrolysis cell stacks to be provided in the electrolysis system, which can be interconnected in any desired manner, e.g., connected in series or in parallel. In this case, each cathode section and each anode section of each electrolysis cell stack is fluidly coupled to the connections mentioned herein in the manner described herein.
[0008] The electrolysis cell stack can in particular be a solid oxide electrolysis system or solid oxide electrolyzer cell system (also SOEC system for English “Solid Oxide Electrolyzer Cell System”). The electrolysis cell stack is preferably operated in a co-electrolysis system such that the electrolysis of water (H2O) and carbon dioxide (CO2) is achieved. The electrolytes in the electrolysis cell stack can thus 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 source for providing electricity from a renewable energy source. With such a power source, which is fed from renewable energy sources, the high-temperature electrolysis operation can be designed in an ecologically sustainable manner. The electrolysis cell stack is particularly advantageously designed as a Co-SOEC stack with a Co-SOEC system.Here, water and CO2 are electrolyzed simultaneously to produce syngas. This is a mixture of CO and H2 that can be used in further steps to produce various synthetic fuels and chemicals.
[0009] For the 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, it is possible to extract carbon dioxide from the air, from biogas processes, from industrial exhaust gases, etc. Water can be supplied to the cathode supply section via a first additional supply connection for supplying water. For this purpose, the first additional supply connection, which can be fluidically coupled to the cathode supply connection or the cathode supply section by means of a first additional supply connection, can supply water, preferably in the form of steam, to the cathode supply section.Alternatively or additionally, the water can be evaporated into water vapor in the electrolysis system. The water vapor can be considered part of the cathode gas because it is supplied to the cathode feed section. Any shielding gas supplied to the cathode feed connection can also be considered part of the cathode gas because it is supplied to the cathode feed section.
[0010] From the anode discharge section, the anode exhaust gases are discharged via the anode discharge connection to the anode discharge connection. The anode exhaust gases discharged via the anode discharge connection include, in particular, exhaust air or oxygen discharged from the electrolysis system, especially oxygen-enriched air, as well as catalyst exhaust gases downstream of the catalyst, i.e., combustion products of catalytic combustion. These can be released into the environment, for example, from the anode discharge connection.
[0011] From the cathode discharge section, the generated cathode offgas, which is synthesis gas containing primarily hydrogen gas and carbon monoxide, is fed to the cathode discharge connection. This connection can be connected to a synthesis plant via a suitable synthesis system to provide the synthetic gas for the production of synthetic hydrocarbons. In this synthesis process, typically not all of the synthesis gas can be converted, and / or short-chain hydrocarbons are formed, which are separated.
[0012] Some of the resulting hydrocarbons are unsuitable for their subsequent intended use, for example, because the chains are too short. However, the portion of the hydrocarbons that is unusable for subsequent use contains a chemically stored energy component and can be considered a carbon dioxide source. This gas component is referred to as recycle gas in the context of the present invention.
[0013] To obtain the recycle gas, a method for separating the usable portion of the hydrocarbons is provided, which will be described in more detail later. The recycle gas obtained in this way is then fed to the recycle gas connection of the electrolysis system and made available for reuse in the electrolysis system. The recycle gas can be introduced into the cathode feed connection via this recycle gas connection. The recycle gas thus supplements the cathode feed gas supplied from another source, thus reducing the amount of carbon dioxide required as one of the starting materials in the production of the synthesis gas.
[0014] In other words, it becomes possible to recycle the synthesis gas converted in the synthesis process, which has been converted into an unusable portion of the hydrocarbons, back into the electrolysis system. This also allows the CO2 already converted in the synthesis process to be recycled and made available for recirculation. This increases efficiency in particular, as the recycled portion of the short-chain hydrocarbons reduces the CO2 required to operate the electrolysis system. A further advantage of this technical feature is that the short-chain and thus unusable components of the hydrocarbons, and thus the recycle gas, do not have to be disposed of separately and released into the environment.Last but not least, another advantage is that the recycle gas is typically at a high temperature due to the high operating temperatures of the synthesis process. This high temperature can then be used to preheat the externally supplied cathode feed gases, for example, the CO2 from the CO2 source. By mixing the recycle gas with the cathode feed gas, a mixed temperature is created that is already sufficient as an inlet temperature for the electrolysis system, or at least reduces the required amount of residual heat.
[0015] It can be summarized that the integration of a recycle gas connection and the associated possibility of recycling the unusable part of the production result of the synthesis process brings about an increase in efficiency in both the chemical and energetic sense.
[0016] In order to distinguish components or elements of the same kind or type from one another, such as heat exchangers, shut-off devices, partial paths or bypass paths, the components or elements of the same kind or type mentioned in this description are numbered consecutively and are referred to as first component, second component, third component (or elements), etc., for example first heat exchanger, second heat exchanger, etc. This designation based on the numbering serves solely to distinguish the components or elements of the same kind or type mentioned herein and in no way represents 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 presuppose a first, second and third component of that kind or type, unless the first, second and third components of that kind or type are mentioned in a claim to which the claim in question refers back.
[0017] The connections mentioned here are fluid-carrying, in particular gas-carrying, connections. The connections can be established via various paths or lines, such as pipes or hoses, which are each coupled to one another. Various flow-influencing devices, as mentioned here, such as shut-off devices, can be arranged in the connections. Where reference is made herein to the arrangement of a heat exchanger in one connection and a thermal coupling of the heat exchanger to another connection, these features are to be understood as synonymous due to the function of the heat exchanger. This is because the heat exchanger exchanges the heat of two flows in the respective connections, for example in countercurrent. In this respect, the heat exchanger is actually arranged in each of the two connections, and the heat exchanger also thermally couples both connections.
[0018] Whenever reference is made to control or monitoring, particularly in connection with a shut-off device, this refers to controlling and / or regulating. Even if not explicitly stated, appropriate control electronics and control devices beyond shut-off devices, such as flow meters, may be provided for monitoring purposes.
[0019] The shut-off devices mentioned herein serve at least to stop or allow the flow of the respective fluid, especially gas, flowing through the connections. Controlling the flow rate is also possible depending on the design of the shut-off device used. The shut-off device can be designed in a variety of ways, for example, as a valve, gate valve, shut-off cock, or butterfly valve.
[0020] It can be advantageous if, in an electrolysis system according to the invention, a reformer device is fluidly connected to the recycle gas connection upstream of the recycle gas connection for at least partially reforming the by-products from the synthesis process. The aim of this reforming is, in particular, to reform the recycle gas into carbon dioxide or at least an increased proportion of carbon dioxide in the recycle gas. This enables improved mixing and more efficient conversion in the electrolysis system of the thus increased carbon dioxide concentration. In addition to chemical reforming and the associated advantages of recirculation to the cathode supply connection, such reforming is usually subject to an endothermic process.This means that the reforming process is typically endothermic, and the heat required for reforming is provided, for example, by simultaneous catalytic partial oxidation. As already explained, a certain minimum temperature for the cathode feed gas is necessary for the operation of the electrolysis system. Since the electrolysis system primarily involves high-temperature electrolysis, increasing the temperature of the recycle gas is a further energetic advantage. Here, it is clearly evident that the integration of a reformer device also offers advantages from both a chemical and thermal, and thus energetic, perspective.In addition to complete reforming to CO2 and / or CO or at least an increase in the concentration ratio of CO2, a simple reduction in the chain length of the hydrocarbons may be sufficient to achieve the desired increase in chemical and / or thermal efficiency.
[0021] Further advantages can be achieved if, in an electrolysis system according to the invention, the reformer device has at least one of the following configurations:
[0022] - Steam Reformer,
[0023] - Dry Reformer,
[0024] - CPOX reformer.
[0025] The above list is not exhaustive. Of course, it is also possible for a reformer device to have two or more different reformer modules with different reforming processes. The combination of multiple reformer modules can serve to further improve the desired reforming and, in particular, result in a greater increase in the CO2 concentration. It may even be preferable for a specific design of the reformer to be configured to completely or essentially completely reconvert the recycle gas into a carbon dioxide-containing gas.
[0026] It is also advantageous if, in an electrolysis system according to the invention, at least one controllable synthesis recycle gas connection is arranged upstream of the recycle gas connection for at least partially recirculating the recycle gas into the synthesis process. This means that, in contrast to a long recycle into the electrolysis system, the recycle gas can also be recirculated directly into the synthesis process via a short recycle. This can be provided in addition to or as an alternative to the recycle gas connection into the electrolysis system. Depending on the operating situation and / or the composition of the recycle gas, it can already be advantageous to recirculate the short-chain hydrocarbons of the recycle gas directly to the inlet section of the synthesis device and thus run them through the synthesis again.In other words, the short-chain and thus unusable hydrocarbons are returned to the inlet section of the synthesis device for direct further synthesis to extend the chain length. This can be controlled flexibly, depending, for example, on the current CO2 availability for the electrolysis system, the current energy situation with regard to the need for temperature control of the electrolysis system, but also the current operating situation of the synthesis device and thus, for example, the chemical composition of the recycle gas. The possibility of recirculating the recycle gas directly into the synthesis via the synthesis recycle gas connection thus allows for flexible control with regard to a short recycle directly into the synthesis device and a long recycle back into the electrolysis system.Such control can be purely qualitative and / or quantitative.
[0027] It may also be advantageous if, in an electrolysis system according to the invention, the synthesis recycle gas connection is arranged upstream of a reformer device. As already explained, reformer devices can provide advantages for adapting the recycle gas for reuse in the electrolysis system. For recirculating the recycle gas via the short recycle gas connection directly into the synthesis device, such reforming is not necessary and may even be detrimental. Particularly if, in the case of short-chain hydrocarbons in the recycle gas, the repeated synthesis is intended to lengthen the existing chains, reforming and thus further shortening the chains before this short recirculation would potentially be counterproductive.According to the invention, the reformer device in this embodiment is arranged downstream of the synthesis recycle gas connection, so that, in particular with flexible and freely controllable shut-off devices, for example control valves, the volume flow can be diverted upstream of the reformer device and fed to the short recycle connection. It can also be advantageous if a recycle gas catalyst device is connected to the recycle gas connection upstream of the recycle gas connection in a fluid-communicating manner. Such a recycle gas catalyst device can be integrated into a reformer device or at least partially form it. However, it is also possible for such a recycle gas catalyst device to be integrated into an electrolysis system according to the invention independently of a reformer device or even without a reformer device.The catalytic conversion of the recycle gas serves in particular to increase the temperature of the recycle gas through catalyzed chemical conversion of components of the recycle gas. As already explained several times, one aim of the present invention is to improve the energetic and, in particular, the thermal efficiency during operation of the electrolysis system. Thus, the use of such a recycle gas catalyst device supports this increase in thermal efficiency, since by increasing the temperature of the recycle gas, it can be used to preheat the externally supplied carbon dioxide. The internal recirculation of the energy contained in the recycle gas as heat to heat the recycle gas thus increases the overall efficiency during operation of the electrolysis system and the electrolysis plant in accordance with the invention.
[0028] It is also advantageous if, in an electrolysis system according to the invention, the recirculation gas connection is integrated into the cathode supply connection. This is, in particular, a design configuration that further reduces the overall complexity of the electrolysis system. For example, the cathode supply connection can have an integrated shut-off device that provides a controlled introduction of the recirculation gas in a quantitative and / or qualitative manner. In particular, it is thus possible to switch the recirculation of the recirculation gas on and off and / or even to control it in a quantifiable manner.
[0029] It is also advantageous if, in an electrolysis system according to the invention, the cathode supply connection and the recycle gas connection each have at least one control valve for controlling the volume flow of recycle gas and cathode supply gas. While purely qualitatively switching control valves would generally fulfill the purpose of controlling and thus controlling, quantitative switching using variably switchable control valves offers further advantages. Particularly when integration into a short recycle cycle with the aid of a synthesis recycle gas connection is planned, such quantitatively adjustable and thus controllable control valves can offer the advantage of flexibly and freely adapting volume flows and their relationships to one another to the respective operating situation.In other words, it is now possible to respond flexibly to the actual composition of the recycle gas, the temperature conditions in the synthesis process and in the electrolysis system, and / or the temperature conditions in the cathode feed gas. Through flexible and thus complex control of the individual volume flows, efficiency can be further increased and the core concept of the invention further improved.
[0030] The present invention also relates to an electrolysis plant comprising an electrolysis system according to the invention and a synthesis system comprising a synthesis plant. The cathode discharge connection is fluidly coupled to the synthesis plant by means of a synthesis gas supply connection. The synthesis plant is also configured for synthesizing synthetic hydrocarbons from synthesis gas generated in the electrolysis cell stack and supplied via the synthesis gas supply connection. Finally, the synthesis plant is fluidly coupled to a recycle gas connection by means of a recycle gas discharge connection for providing recycle gas. Thus, an electrolysis plant according to the invention offers the same advantages as those explained in detail with reference to the electrolysis system according to the invention.
[0031] It can be advantageous if, in an electrolysis plant according to the invention, the recycle gas discharge connection is fluidly connected to a hydrocarbon discharge connection of the synthesis plant via a separation device for separating the gaseous by-products from the synthesis as recycle gas. In addition to the generally known separation of so-called tail gases, also called residual gases, the integration of a separation device into the discharge device for the generated synthesis gas can provide the aforementioned possibility of reusing the recycle gas. Such a separation device can be based on physical and / or chemical separation functionalities and, in particular, operates continuously. This ensures that the usable portion of the synthesis products, i.e. those hydrocarbons with a sufficient chain length, can be separated from the unusable portion, which, for example, has chain lengths that are too short.The separated part from the separation device is passed on to the return gas connection as return gas.
[0032] It may also be advantageous if, in an electrolysis system according to the invention, the recycle gas discharge connection is fluidly connected to the synthesis gas supply connection for at least partial recirculation of the recycle gas into the synthesis system. This can be achieved, for example, using a synthesis recycle gas connection, as already explained with reference to an electrolysis system according to the invention. This means that, in addition to a long recycle cycle into the electrolysis system, a short recycle cycle directly into the synthesis process is now also available as an alternative, with the aforementioned advantages.
[0033] The present invention also relates to a process for producing synthesis gas by means of an electrolysis system, in particular the electrolysis system according to the invention and furthermore very particularly by means of the electrolysis plant according to the invention, comprising the steps:
[0034] - feeding recycle gas separated from a synthesis process in which synthesis gas is converted into hydrocarbons to a recycle gas connection of an electrolysis system,
[0035] - feeding the recycle gas into the cathode feed connection (500) of the electrolysis system (10).
[0036] Thus, a method according to the invention brings with it the same advantages as have been explained in detail with reference to the electrolysis system according to the invention.
[0037] In particular, the electrolysis system according to the invention and / or the electrolysis plant according to the invention can be set up or designed to carry out the method according to the invention.
[0038] The anode gas is understood to mean the gas supplied to the anode section, in particular air or oxygen. This excludes the anode exhaust gas, i.e., the exhaust gas discharged from the anode section, in particular air and / or oxygen. The cathode gas is understood to mean the gas supplied to the cathode section, in particular carbon dioxide, water vapor, and / or a protective gas. This excludes the cathode exhaust gas, i.e., the synthetic gas discharged from the cathode section.
[0039] It is also advantageous if the synthesis process is a Fischer-Tropsch process. The coupling of high-temperature electrolysis, in particular high-temperature co-electrolysis, and Fischer-Tropsch synthesis (FTS for short) has proven to be a particularly promising variant for the production of various hydrocarbons. In FTS, synthesis gas produced from high-temperature co-electrolysis is converted into hydrocarbon molecules with various 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, with the help of a catalyst, particularly a Co- or Fe-based one. The FTS process is highly exothermic. To maintain the temperature within the specified temperature range, cooling can be carried out along the length of a reactor in the synthesis plant. Cooling can be achieved by water evaporation at the specified pressure level.The steam can subsequently be used for further process steps and, as previously mentioned, for the high-temperature electrolysis itself by adding the steam to the cathode gas. The hydrocarbon chain length distribution resulting from FTS is described by a chain growth probability (a high chain growth probability results in large molecules and thus a shift towards liquid fuels). However, the synthesis gas is not fully converted. Furthermore, depending on the chain growth probability, short-chain molecules are formed that cannot be used as liquid fuel. The unconverted synthesis gas and the resulting short-chain hydrocarbons can be separated as the residual gas during product processing. While some of the residual gas can be recirculated into the FTS, some must be discharged. In particular, the discharged portion of the residual gas is utilized in the process according to the invention.
[0040] 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. They show schematically: Fig. 1 shows a first embodiment of an electrolysis plant according to the invention,
[0041] Fig. 2 shows a second embodiment of an electrolysis plant according to the invention,
[0042] Fig. 3 shows a third embodiment of an electrolysis plant according to the invention,
[0043] Fig. 4 shows a fourth embodiment of an electrolysis plant according to the invention and
[0044] Fig. 5 shows a further embodiment of a fuel cell system according to the invention.
[0045] Identical or functionally equivalent elements are designated by the same reference numeral in Figures 1 to 5.
[0046] Figure 1 schematically shows an electrolysis plant 30 comprising an electrolysis system 10 with an electrolysis cell stack 100 and a synthesis system 20 with a synthesis plant 900. The electrolysis system 10 and the synthesis system 20 are fluidically coupled to one another, as will be explained in more detail later.
[0047] By way of example, only one electrolysis cell stack 100 is shown in Fig. 1. However, it is possible to provide multiple electrolysis cell stacks 100. The electrolysis cell stack 100 has a cathode section 110 with a cathode supply section 112 and a cathode discharge section 114. The electrolysis cell stack 100 also has an anode section 120 with an anode supply section 122 and an anode discharge section 124. A power supply source 130, which provides electricity from renewable energies, is connected to the electrolysis cell stack 100. The electrolysis cell stack 100 is presently designed as a solid oxide electrolysis cell stack and is used in reverse mode for high-temperature co-electrolysis.
[0048] Anode gas in the form of fresh air is provided to the electrolysis system 10 by means of 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 in the form of an air filter, for air filtration and a fan 206 for transporting the anode gas are arranged in the anode supply connection 200.
[0049] A first heat exchanger 220 is arranged in the anode supply connection 200, downstream of the filter device 204 and the blower 206, in the flow direction of the anode gas from the anode gas connection 202 to the anode supply section 122. The first heat exchanger 220 is used for heat exchange with a warm anode exhaust gas, in particular in the form of exhaust air discharged from the anode section 120, from the electrolysis cell stack 100. For this purpose, the first heat exchanger 220 is thermally coupled to an anode discharge connection 300 upstream of a catalyst 404 in the form of an oxidation catalyst. The anode discharge connection 300 fluidically connects the anode discharge section 124 to an anode discharge connection 316.
[0050] As Figure 1 shows, a recycle gas connection 520 is provided as a further connection as part of the electrolysis system 10. The downstream synthesis plant 900 produces production gas, which in particular has different chain lengths of hydrocarbons. With the aid of a separation device 932, shown schematically here, the produced gas is then divided into usable and unusable components, in particular with regard to the existing chain length of the hydrocarbons. Chain lengths of the hydrocarbons that are too short for the intended use are then introduced as unusable recycle gas from the separation device 932, separate from the usable portion, which can be referred to as useful gas, into the recycle gas discharge connection 930. This recycle gas discharge connection 930 is fluidly connected to the recycle gas connection 520.
[0051] The recycle gas, i.e., the short-chain hydrocarbons, are now introduced directly into the cathode feed connection 500, thus providing a supplement to the starting materials for carrying out the chemical process in the electrolysis cell stack 100. This ensures at least the chemical recycle as a long recycle cycle. As an alternative to direct introduction into the cathode feed connection 500, an indirect, particularly controlled, introduction can also be provided. In particular, such a controlled introduction can allow for a targeted adjustment and / or modification of the gas composition in the cathode feed connection 500.
[0052] 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 220 with the anode discharge connection 300 upstream of the catalyst supply section 406 and thus allows the air content of the anode exhaust gas to be further increased before entering the catalyst 404.
[0053] In addition, a second bypass path 212 with a second shut-off device 214 is provided, which connects the anode supply connection 200 upstream of the first heat exchanger 220 in the flow direction of the anode gas with the anode supply connection 200 downstream of the first heat exchanger 220 in the flow direction of the anode gas, thereby making it possible to control the temperature of the anode exhaust gas upstream of the catalyst 404 by regulating the amount of anode gas flowing through the first heat exchanger 220. Furthermore, a third shut-off device 218 is arranged upstream of the second heat exchanger 220 and downstream of the second bypass path 212 in the flow direction.
[0054] The hot catalyst exhaust gases flow in the anode exhaust connection 300 through two individual sub-paths 302, 308, into which the anode exhaust connection 300 divides in the flow direction of the catalyst exhaust gas downstream of the catalyst exhaust section 408. Located in the first sub-path 302 is a second heat exchanger 304, which is thermally coupled to the anode supply connection 200. This allows the heat of the catalyst exhaust gas to be transferred to the anode gas upstream of the anode supply section 122. Downstream of the second heat exchanger 304 is a fourth shut-off device 306 for controlling the catalyst exhaust gas flow in the first sub-path 302.
[0055] Located in the second partial path 308 is a third heat exchanger 310 with a fifth shut-off device 312 arranged downstream of it in the flow direction of the catalyst exhaust gas. The third heat exchanger 310 is thermally coupled to a cathode supply connection 500. The cathode supply connection 500 fluidically connects a cathode supply connection 502 to the cathode supply section 112. In the cathode supply connection 500, cathode gas, in particular carbon dioxide, is supplied from the cathode supply connection 502 to the cathode supply section 112. An ejector 504 is arranged in the cathode supply connection 500 upstream of the cathode section 110 in the flow direction of the cathode gas. Furthermore, a second heating device 506, in the form of an electric heater, is arranged downstream of the ejector 504 in the direction of flow of the cathode gas. The third heat exchanger 310 allows the cathode gas to be heated using heat from the catalyst exhaust gas.
[0056] In the embodiment of Fig. 1, a fourth heat exchanger 314 is located in the anode discharge connection 300 downstream of the second heat exchanger 304 and the third heat exchanger 310 in the flow direction of the catalyst exhaust gas. The fourth heat exchanger 314 is thermally coupled to a first auxiliary supply connection 700, which fluidically connects a first auxiliary supply connection 702 to the cathode supply connection 500. Water or steam is provided from the first auxiliary supply connection 702 for the high-temperature co-electrolysis, which is heated by the fourth heat exchanger 314 and flows to the cathode supply connection 500.
[0057] By means of a cathode discharge connection 600, which fluidically connects the cathode discharge section 114 to a cathode discharge connection 612, cathode exhaust gas in the form of the synthesis gas generated by the high-temperature co-electrolysis, comprising hydrogen and carbon monoxide, is discharged to the synthesis system 20. Two heat exchangers 608, 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 in order to transfer heat from the synthesis gas to the cathode gas and thus increase the efficiency of the electrolysis system 10.
[0058] A second additional supply connection 800 fluidically connects a second additional supply connection 802 for supplying a protective gas to the cathode supply connection 500. The second additional supply connection 800 is divided, for example, into two sub-paths 804, 806, namely a third sub-path 804 and a fourth sub-path 806. The third sub-path 804 leads to the cathode supply connection 500 upstream of the ejector 504 and, in particular, upstream of the heat exchangers 608, 610, while the fourth sub-path 806 leads to the ejector 504. A third bypass path 602 leads from the cathode discharge section 600 to the fourth partial path 806 upstream of the ejector 504. In the third bypass path 602, a nozzle 604, in particular a Venturi nozzle, and a sixth shut-off device 606, in particular a valve, are arranged.
[0059] 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 the cathode exhaust gas in the form of synthesis gas comprising hydrogen and carbon monoxide, and the anode exhaust gas comprising exhaust air in reverse mode by high-temperature co-electrolysis. The anode exhaust gas is catalytically combusted by the catalyst 404, so that catalyst exhaust gases are separated from the electrolysis system 10 at the anode discharge connection 316.
[0060] The synthesis gas is provided to the synthesis system 900 of the synthesis system 20 via a synthesis gas supply connection 906, which fluidically connects a synthesis supply section 902 of the synthesis system 900 to the cathode discharge connection 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 fluidically connected to a synthesis discharge section 904.
[0061] Figure 2 builds on the technical solution of Figure 1. In this embodiment, however, a reformer device 522 was additionally positioned upstream of the recycle gas connection 520. Such a reformer device serves in particular to reform the recycle gas, for example, to further shorten the chain length of the hydrocarbons in the recycle gas. Reforming to an increased concentration of carbon dioxide is also conceivable here as part of the reformer device. This makes it possible, on the one hand, to improve the chemical usability in the electrolysis cell stack 100, thereby increasing the chemical efficiency. If this reforming takes place as an endothermic reforming and thus requires an increase in temperature, catalytic oxidation can provide the necessary heat.The elevated-temperature recycle gas can now be mixed with a cathode feed gas via an external source at the cathode feed port 502. This mixing and its own elevated temperature will directly lead to an increased mixing temperature of the mixed gas as the cathode feed gas. In addition to increasing chemical efficiency, this also enables an increase in thermal efficiency.
[0062] Figure 3 also shows a further development of the embodiment of Figure 1. Here, a synthesis recycle gas connection 530 is provided, which is arranged upstream of the recycle gas connection 520. In this way, two parallel recycle options are provided. A long recycle cycle into the electrolysis system 10 and thus the electrolysis cell stack 100 is ensured via the recycle gas connection 520. Alternatively, a short recycle cycle can be operated via the synthesis recycle gas connection 530, for example, which can also be controlled with the aid of shut-off devices or control valves. In this recycle cycle, the recycle gas is recirculated, so to speak, past the electrolysis system 10 directly into the synthesis gas supply connection 906, thus serving for direct and repeated synthesis starting from the recycle gas.
[0063] Figure 4 also shows another further development of the embodiment of Figure 1. Here, a recycle gas catalyst device 524 is provided, which can, for example, at least partially carry out reforming through a catalytic chemical conversion of the recycle gas. The core idea of using a recycle gas catalyst device 524, however, is to achieve an increase in the temperature of the recycle gas through the catalytic conversion of at least some components of the recycle gas. As already explained, the increased temperature, in particular the catalytically further increased temperature of the recycle gas, results in an increased mixing temperature with the externally supplied cathode feed gas, so that the thermal efficiency during operation of the electrolysis system 10 increases accordingly.
[0064] Figure 5 shows an alternative embodiment. This is a variant with a heating device 230 in a separate path of the anode supply connection 200. This separate path can be switched qualitatively and / or quantitatively as a bypass using valves (not shown). In this way, the controllability, in particular the adjustability of the operating mode, can be further improved. This embodiment can also be applied to all other variants, in particular those shown in Figures 1 to 4.
[0065] The above explanations of the embodiments describe the present invention exclusively by way of examples. List of reference symbols
[0066] 10 Electrolysis system
[0067] 20 Synthesis system
[0068] 30 electrolysis plant
[0069] 100 electrolysis cell stacks
[0070] 110 Cathode section
[0071] 112 Cathode feed section
[0072] 114 Cathode discharge section
[0073] 120 anode section
[0074] 122 Anode feed section
[0075] 124 Anode discharge section
[0076] 130 Power source
[0077] 200 Anode feed connection
[0078] 202 Anode feed connection
[0079] 204 Filter device
[0080] 206 blowers
[0081] 208 first bypass path
[0082] 210 first shut-off device
[0083] 212 second bypass path
[0084] 214 second shut-off device
[0085] 216 first heating device
[0086] 218 third shut-off device
[0087] 220 first heat exchanger
[0088] 230 heater
[0089] 300 anode discharge connection
[0090] 302 first partial path
[0091] 304 second heat exchanger
[0092] 306 fourth shut-off device
[0093] 308 second part path
[0094] 310 third heat exchanger
[0095] 312 fifth shut-off device
[0096] 314 fourth heat exchanger
[0097] 316 anode discharge connection
[0098] 318 fifth heat exchanger
[0099] 320 Heat exchanger Residual gas supply connection Residual gas supply connection Catalyst
[0100] Catalyst feed section
[0101] Catalyst discharge section catalyst
[0102] Catalyst feed section
[0103] Catalyst discharge section
[0104] Cathode supply connection
[0105] Cathode supply connection
[0106] Ejector second heating device recirculation gas connection reformer device
[0107] Recycle gas catalyst device Synthesis recycle gas connection Cathode discharge connection Third bypass path
[0108] Nozzle sixth shut-off device sixth heat exchanger seventh heat exchanger cathode discharge connection first additional feed connection first additional feed connection second additional feed connection second additional feed connection third sub-path fourth sub-path synthesis plant synthesis feed section
[0109] Synthesis discharge section
[0110] Synthesis gas supply connection Hydrocarbon discharge connection Residual gas discharge connection Cooling device Third additional supply connection Recycle gas discharge connection Separation device
Claims
Patent claims 1. Electrolysis system (10), comprising: - an electrolytic 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 (316) fluidly coupled to the anode discharge section (124) by means of an anode discharge connection (300) for discharging anode exhaust gases generated by the electrolysis cell stack (100), - 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 electrolysis system (10) further comprises: - a recycle gas connection (520) for providing recycle gas which is produced as a by-product in a subsequent synthesis process for producing synthetic hydrocarbons from synthesis gas generated in the electrolysis cell stack (100), wherein the recycle gas connection (520) is fluidly connected to the cathode supply connection (500).
2. Electrolysis system (10) according to claim 1, characterized in that upstream of the recycle gas connection (520) a reformer device (522) is fluidly connected to the recycle gas connection (520) for at least partially reforming the by-products from the synthesis process.
3. Electrolysis system (10) according to claim 2, characterized in that the reformer device (522) has at least one of the following configurations: - Steam Reformer - Dry Reformer - CPOX reformer 4. Electrolysis system (10) according to one of the preceding claims, characterized in that at least one controllable synthesis recycle gas connection (530) is arranged upstream of the recycle gas connection (520) for at least partially recirculating the recycle gas into the synthesis process.
5. Electrolysis system (10) according to claim 4, characterized in that the synthesis recycle gas connection (530) is arranged upstream of a reformer device (522).
6. Electrolysis system (10) according to one of the preceding claims, characterized in that upstream of the recirculation gas connection (520) a recirculation gas catalyst device (524) is fluidly connected to the recirculation gas connection (520).
7. Electrolysis system (10) according to one of the preceding claims, characterized in that the return gas connection (520) is integrated into the cathode supply connection (502).
8. Electrolysis system (10) according to one of the preceding claims, characterized in that the cathode supply connection (502) and the recirculation gas connection (520) each have at least one control valve for controlling the volume flow of recirculation gas and cathode gas.
9. Electrolysis plant (30) with an electrolysis system (10) according to one of the preceding claims and a synthesis system (20) with a synthesis plant (900), wherein - the cathode discharge connection (612) is fluidically coupled to the synthesis plant (900) by means of a synthesis gas supply connection (906), - the synthesis plant (900) is designed to synthesize synthetic hydrocarbons from synthesis gas produced 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 a recycle gas connection (520) by means of a recycle gas discharge connection (930) for providing recycle gas.
10. Electrolysis plant (30) according to claim 9, characterized in that the recycle gas discharge connection (930) is fluidly connected via a separating device (932) to a hydrocarbon discharge connection (908) of the synthesis plant (900) for separating the gaseous by-products from the synthesis as recycle gas.
11. Electrolysis plant (30) according to one of claims 9 or 10, characterized in that the recycle gas discharge connection (930) is fluidly connected to the synthesis gas supply connection (906) for at least partially recirculating the recycle gas into the synthesis plant (900).
12. A method for producing synthesis gas by means of an electrolysis system (10) according to one of claims 1 to 8, comprising the steps: - feeding recycle gas separated from a synthesis process in which synthesis gas is converted into hydrocarbons to a recycle gas connection (520) of an electrolysis system (10), Feeding the recycle gas into the cathode feed connection (500) of the electrolysis system (10).