Electrolysis System

Abstract

The present invention relates to a solid oxide electrolyzer cell system (10) comprising an electrolysis stack (12) comprising an anode, a cathode, and a solid oxide electrolyte. The anode comprises an anode inlet (14). The system (10) further comprises a sweep gas source (16) for supplying a sweep gas to the anode via the anode inlet (14), and a sweep gas supply flow path (18) defining a flow path between the sweep gas source (16) and the anode inlet (14). The system (10) further comprises a first heat exchanger (30) in fluid communication with the sweep gas supply flow path (18). The first heat exchanger (30) has a source external to the solid oxide electrolyzer cell system (10) and is also in fluid communication with a fluid stream (26) defining an external flow path (28). The first heat exchanger (30) is configured to exchange heat between the sweep gas supply flow path (18) and the external flow path (28). The invention further relates to a method of operating such a solid oxide electrolyzer cell system (10) by exchanging heat between the external flow path (28) and the sweep gas supply flow path (18) via a first heat exchanger (30).

Description

[Technical field]

[0001] The present invention relates to an electrolysis or electrolyzer system for producing hydrogen (or synthesis gas) by electrolysis of water (and carbon dioxide) in a cell with an electrolyte. One form of such a cell is the solid oxide electrolyzer cell, or SOEC. [Background technology]

[0002] Electrolysis systems generally comprise one or more cells having an electrolyte, an anode and a cathode, which operate to produce hydrogen by the electrolysis of water, or synthesis gas by the electrolysis of water and carbon dioxide.

[0003] To produce hydrogen, the cell is supplied with water (in the form of steam) at the cathode and a reducing gas or fuel at the anode. A DC current is then supplied between the anode and cathode. The water (steam) then undergoes reduction such that the steam is reduced to hydrogen gas and oxygen, which electrochemically converts the fuel across the electrolyte to provide exhaust gas at the anode side, and hydrogen is output as a gas at the cathode side.

[0004] A characteristic of electrolyzer systems is that they tend to be energy inefficient. Much of this is due to the fact that they operate most effectively at temperatures well above room temperature, typically 500-800 °C. To achieve these temperatures at start-up, electrolyzer systems generally use heaters to warm the system up to operating temperature, typically by heating the input fluid streams (hot steam and hot fuel). Electrolyzer systems also need to maintain fluid supplies at high temperatures during system operation to maintain efficient operation of the electrolyte. Additionally, electrolyzer systems emit off-gases (exhaust gas and hydrogen) at high temperatures, which also wastes energy.

[0005] Prior art systems are known that use a heat exchanger to utilize the heat of the exhaust gas to heat the steam before it is injected into the cathode side. See, for example, US Patent Application Publication Nos. 2007217995(A1) and 2009235587. However, this has the drawback that exhaust gas is only produced when the system is running. This results in a lack of heat available during start-up. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an object of the present invention to more efficiently utilise the heat flow paths during start-up, operation, cool-down etc. It is a further object of the present invention to increase the operational efficiency of the electrolyser system. [Means for solving the problem]

[0007] According to the present invention, there is provided a solid oxide electrolyzer cell system comprising: an electrolysis stack comprising an anode, a cathode, and a solid oxide electrolyte, the anode comprising an anode inlet; a sweep gas source for supplying a sweep gas to the anode via the anode inlet; a sweep gas supply passage defining a flow path between a sweep gas supply and the anode inlet; a first heat exchanger in fluid communication with the sweep gas supply passage; the first heat exchanger has a source external to the solid oxide electrolyzer cell system and is also in fluid communication with a fluid stream defining an external flow path; A solid oxide electrolyzer cell system is provided, wherein a first heat exchanger is configured to exchange heat between the sweep gas supply passageway and the external passageway.

[0008] The external flow path may be available from a variety of sources. The external flow path is outside the operation of the solid oxide electrolyzer cell system. It is therefore a separate process. This heat may otherwise be wasted or not utilized. The use of steam to heat the sweep gas supply flow path increases the efficiency of the electrolysis stack. The heat from the external stream may be of any grade. For example, low grade heat below 200°C may be used.

[0009] The use of an external flow can be particularly useful during start-up of the electrolyzer system when the electrolysis stack produces little or no heat. Thus, the external flow provides a level of heat to the sweep gas supply passage and thus the anode inlet to improve start-up efficiency and reduce heat supplied from other sources (e.g., heaters).

[0010] Preferably, the system includes a bypass flow path connected to the sweep gas supply flow path, the bypass flow path being connected at a first end thereof to a location upstream of the first heat exchanger, and the bypass flow path being connected at a second end thereof to a location downstream of the first heat exchanger.

[0011] The bypass flow path allows the sweep gas supply flow path to be bypassed around the external flow path connected to the first heat exchanger. The flow can therefore be directed towards the anode inlet without heat exchange. This can be useful when the transfer of heat from the external fluid flow is insufficient to heat the sweep gas supply flow path. In some cases, the external heat source may not be operational and therefore it may be desirable to avoid heat exchange with the external flow, as this would reduce the temperature of the sweep gas supply flow path.

[0012] Additionally, a bypass path can be utilized, for example in a heat exchanger, when the maximum possible heat recovery for a component limit is exceeded, thus avoiding damage to the system using the bypass path.

[0013] Preferably, the system comprises a first heater positioned in the sweep gas supply passage and connected downstream of the first heat exchanger. Such a first heater can make fine adjustments for the heating of the sweep gas supply in the sweep gas inlet passage. In particular, the amount of additional heat desired for the anode inlet changes after heat exchange with the external fluid flow. The first heater can adjust the heat supplied. The amount of heat energy supplied by the first heater can be reduced as needed to take into account other heat sources, thus increasing the overall efficiency of the system.

[0014] Preferably, the first heater is an electric heater or a combustion heater. This heater may also be called a trim heater. The first heater may also be called an inlet heater or a sweep gas heater.

[0015] Preferably, the first heater is positioned after the bypass passage, so that the first heater can heat the sweep gas supply passage when necessary and is not bypassed. Instead, the first heater is controlled to provide the required level of heat energy and to stop providing heat when not required. The degree of heat provided can also be varied.

[0016] The sweep gas is CO 2 , O 2 , N 2 The sweep gas may be any number of gases, such as Ar, Ar, etc. The sweep gas may be air. In general, any gas that does not react with oxygen may be used as the sweep gas. The sweep gas may be referred to as a reducing gas.

[0017] Preferably, the system comprises: an anode outlet for an anode of the electrolysis stack, an anode outlet comprising an anode outlet flow path defining a flow path between the anode outlet and the first outlet; a second heat exchanger in fluid communication with the sweep gas supply passage and positioned downstream of the first heat exchanger in the sweep gas supply passage, the second heat exchanger also in fluid communication with the anode outlet passage and configured to exchange heat between the sweep gas supply passage and the anode outlet passage.

[0018] As a result of the electrolytic reaction in the stack, exhaust gas is produced and output through the anode outlet. This exhaust gas is then discharged from the outlet, i.e. the first outlet. However, the exhaust gas contains energy in the form of heat. The exhaust gas may have a temperature in the range of 500°C to 650°C. Therefore, it is also beneficial to use this heat. The second heat exchanger provides an additional means of heating the sweep gas supply passage.

[0019] The second heat exchanger is downstream of the first. When the exhaust gas has a higher temperature than the external supply stream, such as during full operation after warm-up, the temperature of the sweep gas supply stream must be increased before it reaches the anode inlet. The sequential heating through the heat exchanger increases system efficiency.

[0020] Preferably, in some embodiments, the first heat exchanger is located downstream of the second heat exchanger, which can be advantageous when the external stream is particularly high-grade heat and therefore an increased order of heat exchange is preferred.

[0021] The bypass flow path can also bypass the second heat exchanger. Thus, the sweep gas supply flow path does not pass through the first and second heat exchangers. This can be useful during start-up, when the anode exhaust gas temperature can be lower than the sweep gas supply temperature. As mentioned above, it is also useful to protect components that may exceed their limits.

[0022] The terms low-grade and high-grade heat are used to describe the quality or level of heat in the flow path. If the process produces heat as a by-product, this is called waste heat and is often classified as low-grade, medium-grade, and high-grade depending on the temperature. Other terms such as waste heat or secondary heat are also used. For the purposes of this description, low-grade heat is considered to be in the range of 150°C to 300°C, although lower temperatures may be utilized. The term high-grade heat is also used, meaning temperatures in the range of 500°C and above. However, for the purposes of this description, temperatures above 350°C may also be considered high-grade.

[0023] In some embodiments, the bypass flow path preferably bypasses only the first or second heat exchanger.

[0024] Preferably, the system comprises: a cathode inlet for the cathode of the electrolysis stack; a fuel supply for supplying fuel to the cathode via the cathode inlet; a fuel supply channel defining a flow path between a fuel supply and the cathode inlet; a cathode outlet for the cathode of the electrolysis stack; a cathode outlet flow path defining a flow path between the cathode outlet and the second outlet; and a third heat exchanger in fluid communication with the downstream side of the fuel supply passage, the third heat exchanger also in fluid communication with the cathode outlet passage and configured to exchange heat between the fuel supply passage and the cathode outlet passage.

[0025] The electrolysis reaction in the stack produces hydrogen gas (or sometimes synthesis gas) which is output through the cathode outlet. This may be called product, product gas or fuel. The product is then sent to an outlet and used for various other processes. The product at the cathode outlet has high-grade thermal energy in the range of 500°C to 650°C. Therefore, heat from here may also be used to heat the sweep gas inlet passage. This ensures a supply of hot steam to the cathode inlet.

[0026] Preferably, the system comprises a cathode outlet branch flow path connecting and fluidly connecting the cathode outlet flow path and the anode outlet flow path.

[0027] It is advantageous to have a cathode outlet branch connected to the anode outlet channel also for providing thermal energy for transfer in the second heat exchanger, said branch allowing a partial flow of products from the cathode outlet channel to the anode outlet channel leading to the first outlet.

[0028] Preferably, the system comprises a valve disposed in the cathode outlet branch, which allows control of the flow of product gas to the anode outlet. It may be advantageous to only use the branch, especially during start-up, when an increase in the temperature of the sweep gas supply path is required.

[0029] Preferably, the system comprises a fourth heat exchanger in fluid communication with the fuel supply passage and also in fluid communication with the external passage and configured to exchange heat between the passages.

[0030] A fuel supply is connected to the cathode inlet for the electrolysis reaction in the stack. The fuel supply is usually water, more precisely steam. It is advantageous to heat the fuel supply passage for a more efficient electrolysis reaction in the stack. This further ensures that the water is heated to a level that supplies the steam. Thus, by using the external passage to also heat the fuel supply, low-grade heat can be utilized for both passages to the anode inlet and the cathode inlet. The external passage can be divided to have one passage for the first heat exchanger and one passage for the fourth heat exchanger for this purpose.

[0031] Preferably, the external flow path for the fourth heat exchanger is a second flow path supplying the fourth heat exchanger which is different from the flow path supplying the first heat exchanger.

[0032] Preferably, the third heat exchanger in fluid communication with the fuel supply flow path is downstream of the fourth heat exchanger in that flow path. The third heat exchanger is in fluid communication with the cathode outlet flow path and configured to exchange heat between the fuel supply flow path and the cathode outlet flow path.

[0033] As mentioned above, when the stack is in full operation, the output from the cathode outlet has high-grade heat. This heat can also be used to heat the fuel supply flow path. This ensures a high-temperature steam supply to the cathode inlet. A fourth heat exchanger can be added to the third heat exchanger. Alternatively, the third and fourth heat exchangers can form separate embodiments. Similarly, the third and fourth heat exchangers can be in a system that does not include a branch flow path connecting the cathode outlet flow path to the anode outlet flow path.

[0034] Preferably, in some embodiments, the fourth heat exchanger is downstream of the third heat exchanger in the fuel supply flow path, which may be advantageous when the external flow path is a high quality heat flow path.

[0035] Preferably, the system comprises a second heater positioned in the fuel supply flow path and arranged downstream of the third heat exchanger in this flow path. Preferably, the second heater is arranged downstream of the fourth heat exchanger. Such a second heater can make fine adjustments for the heating of the fuel supply in the fuel supply flow path. In particular, after heat exchange with either or both of the third and fourth heat exchangers, the amount of heat required at the cathode inlet changes. The second heater can adjust the heat supplied. Furthermore, this can increase energy efficiency, since the heat supplied by the second heater can be reduced when it is not needed. The second heater can be called a (further) inlet heater or a fuel supply heater.

[0036] Preferably, the second heater is an electric heater or a combustion heater.

[0037] Preferably, the system includes a third heater positioned in the anode outlet flow path between the anode outlet and the second heat exchanger. The third heater allows for heating of the anode outlet flow path to increase the heat exchanged with the sweep gas supply flow path. A third heater in this flow path may be particularly useful during start-up when the anode exhaust gas has a lower level of thermal energy.

[0038] The burner is a fired heater or an electric heater. It may also be called a stack outlet heater, an anode exhaust gas heater, or a burner. Preferably, when the third heater is a fired heater, a fuel supply is provided for the third heater.

[0039] Preferably, the third heater is fueled by an external fuel supply. The anode exhaust gas may not be combustible. Thus, an external fuel supply may be provided to the burner to heat the anode exhaust gas, allowing heat exchange with the sweep gas supply passage. This is particularly advantageous during start-up or heat-up of the stack.

[0040] If a branch flow path is provided, it is preferable to connect the branch flow path to a third heater. The cathode outlet gas is a combustible gas (e.g., hydrogen or synthesis gas), which can be burned in a burner. This heats the anode outlet flow path, which in turn heats the sweep gas supply flow path in the second heat exchanger. This can be used during start-up. In this case, a valve located in the branch flow path can be opened to allow the product gas to flow from the cathode outlet to the burner. This can be useful when the exhaust gas from the anode outlet is low quality, such as during start-up or heat-up of the stack.

[0041] Preferably, the system comprises a switching valve connected to the anode outlet flow path at a location between the anode outlet and the second heat exchanger, the switching valve also connected to the external flow path and the third outlet, the switching valve configured to direct flow between the anode outlet and the second heat exchanger, the external flow path or the third outlet.

[0042] The diverter valve allows the exhaust gas from the anode outlet to be diverted to a third outlet that does not pass through a heat exchanger, rather than the above-mentioned path of the anode outlet flow path to the second heat exchanger. This can be useful for cooling the system. In such a situation, recuperation (e.g., via the second heat exchanger) is not required. Thus, the diverter valve allows the hot gas to be discharged elsewhere, i.e., through the third outlet. This is also useful when the temperature of the exhaust gas exceeds the thermal limit of the heat exchanger. Thus, the gas is discharged before the second heat exchanger.

[0043] The switching valve can also be connected to the external flow path, which may have a branch flow path for this purpose. This allows low-grade heat flow from an external source to the anode outlet flow path. This may be useful during start-up to heat the external stream and reduce the energy input to the external stream. This is especially the situation where the external flow is warmer than the anode outlet flow passage. This may also be beneficial if an external source provides a combustible gas and allows combustion of this gas in the third heater to generate heat for the sweep gas supply flow passage. The flow may be in either direction, for example towards the anode outlet or towards the second heat exchanger, as required.

[0044] Preferably, the third heater may be connected to the switching valve when the switching valve is present, and the third heater is positioned between the second heat exchanger and the switching valve.

[0045] Preferably, if there is a branch flow path, this may be connected to the anode outlet flow path which is connected to the switching valve.

[0046] Such a configuration allows for great flexibility for the flow and heat transfer around the system. In particular, during start-up, heat can be supplied to the sweep gas supply passage from a variety of sources. Similarly, during cool-down, there is also the option to exhaust heat through a third exhaust.

[0047] In accordance with the present invention, there is provided a method of operating a solid oxide electrolyzer cell system, comprising the steps of: providing a sweep gas source for supplying a sweep gas to an anode of the electrolysis stack via an anode inlet, defining a sweep gas supply passage between the sweep gas source and the anode inlet; forming a fluid stream having a source external to the solid oxide electrolyzer cell system and defining an external flow path from the fluid stream; and exchanging heat between the external flow path and the sweep gas supply flow path via a first heat exchanger.

[0048] The use of an external fluid flow to heat the sweep gas supply passages increases the efficiency of the electrolysis stack, which can be particularly useful during start-up when the system temperature is low and thermal energy cannot be recovered from internal means.

[0049] Preferably, the method of operating a solid oxide electrolyzer cell system defines an anode outlet flow path between an anode outlet of the electrolyzer anode and a first outlet to the system.

[0050] Preferably, the method of operating a solid oxide electrolyser cell system includes exchanging heat between the anode outlet flow path and the sweep gas supply flow path by means of a second heat exchanger disposed in the sweep gas supply flow path at a location downstream of the first heat exchanger.

[0051] If there is enough heat to do so, the exhaust gas from the stack can also be used to heat the sweep gas supply passage. This recuperative heat exchanger relies on the heat quality available from the stack. This reduces the need to provide heat to the sweep gas supply passage from another source.

[0052] Preferably, the method of operating the solid oxide electrolyzer cell system includes bypassing the first and second heat exchangers by a bypass flow path disposed in the sweep gas supply flow path upstream of the first heat exchanger and downstream of the second heat exchanger, allowing the heat exchangers to be bypassed when there is not enough heat to exchange, such as from the external flow path or from the anode outlet flow path.

[0053] Preferably, the method of operating the solid oxide electrolyzer cell system includes supplying heat to the anode outlet flow passage from a third heater disposed in the anode outlet flow passage between the anode outlet and the second heat exchanger. This may be beneficial when heat generated from the anode outlet requires additional heat to exchange with the sweep gas supply flow passage. Situations where this may occur may include start-up where the stack is not producing high grade heat.

[0054] Preferably, the method of operating the solid oxide electrolyzer cell system includes supplying heat to the anode outlet flow path from an external fluid flow path or a third heater by a diverter valve disposed in the flow path between the anode outlet and the burner. There are situations, such as during cool down, where heat exchange with the sweep gas supply flow path is undesirable. Thus, the diverter valve can direct heat from the anode outlet to another path, such as an exhaust. This will increase the cooling rate of the system.

[0055] These and other features of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0056] [Figure 1] FIG. 1 is a schematic diagram of an electrolyzer system having an external flow path for the anode side of the stack. [Diagram 2] FIG. 2 is a schematic diagram of FIG. 1 including a third heater in the anode exhaust gas flow path. [Diagram 3] FIG. 2 is a schematic diagram of FIG. 1, with the external flow passages provided in different positions. [Figure 4] FIG. 2 is a schematic of FIG. 1, with an external flow path provided on the cathode side of the stack. [Diagram 5] FIG. 5 is a schematic diagram of FIG. 4, with the external flow passages provided in different positions. [Figure 6] FIG. 3 is a schematic diagram of FIG. 2 including a diverter valve. [Figure 7] FIG. 2 is a schematic diagram of an electrolyser system similar to FIG. 1, where the external stream flows on the cathode and anode sides are the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Reference will now be made in detail to embodiments of the invention, one or more examples of which are set forth below, each of which is provided by way of explanation of the invention, and not as a limitation of the invention.

[0058] A list of reference numbers used herein is provided at the end of the detailed embodiment description.

[0059] Referring to Figure 1, there is shown an electrolyzer system 10. The electrolyzer system 10 generally comprises an electrolysis stack 12. The electrolysis stack 12 generally comprises an anode and a cathode for a reduction reaction to produce a product.

[0060] The stack 12 has an anode inlet 14 through which the anode of the stack 12 is fed. A sweep gas supply 16 is provided which is connected to the anode inlet 14 by a sweep gas supply passage 18.

[0061] A flow path is described, but generally a flow path is a flow through a pipe or line from one location to another. A flow path thus defines a fluid connection or fluid communication between points. A sweep gas supply flow path 18 is described, but this is also a sweep gas supply pipe or line 18, which forms the fluid communication. For consistency, reference is made to a flow path when possible.

[0062] Generally, a sweep gas is supplied through a sweep gas source 16 and passes through a sweep gas supply passage 18 to the anode inlet 14 .

[0063] The stack 12 includes an anode outlet 20 through which the exhaust product is discharged. This is typically exhaust gas. The anode outlet 20 is connected to a first outlet 22 by an anode outlet flow passage 24. As a result, the exhaust gas produced in the stack 12 is discharged at the anode outlet 20 and passes through the anode outlet flow passage 24 to the first outlet 22.

[0064] The exhaust gas may be utilized for a variety of purposes external to the system 10 .

[0065] An external fluid stream 26 enters the electrolytic cell system 10. The external fluid stream 26 is an external stream that is generated separately from the process of the electrolytic cell system 10. The external fluid stream 26 may be a high temperature stream of fluid or gas.

[0066] The external fluid stream 26 is an exhaust gas from another process and is expected to be a fluid stream with low grade heat (e.g., about 200° C.), although different sources can be utilized to provide higher or lower grade heat to the external fluid stream 26.

[0067] The external fluid stream 26 forms an external flow passage 28. The external flow passage 28 passes through a first heat exchanger 30. The first heat exchanger 30 is also disposed within the sweep gas supply flow passage 18 between the sweep gas supply 16 and the anode inlet 14. Thus, both the external flow passage 28 and the sweep gas supply 18 pass through and exchange heat within the first heat exchanger 30.

[0068] As mentioned above, the external fluid stream 26, and therefore the external flow path 28, is expected to contain thermal energy. Therefore, if the heat content of the sweep gas supply path 18 is low, heat is transferred to the sweep gas supply path 18 in the first heat exchanger 30 before entering the stack 12. This can be beneficial as a hot sweep gas supply 16 at the anode inlet 14 is favorable for the electrolyzer reactions in the electrolysis stack 12.

[0069] In some circumstances, the sweep gas supply passage 18 has a higher temperature than the external passage 28. Thus, heat transfer in the first heat exchanger 30 is from the sweep gas supply passage 18 to the external passage 28. This is generally expected to be undesirable, unless, for example, the temperature of the sweep gas supply passage 18 is to be reduced to cool the stack 12 and the system 10.

[0070] The use of an external fluid stream 26 to supply heat to the system 10, and more specifically to the sweep gas supply passage 18, is beneficial because it does not rely on any process within the system 10 to supply heat to the sweep gas supply passage 18 or other components of the system 10. In particular, when the system 10 is starting up, the electrolyzer reactions in the electrolysis stack 12 do not generate any / significant heat. Therefore, the external fluid stream 26 can independently supply thermal energy to the system 10 and is not dependent on the operating state of the system 10.

[0071] 1 also shows that the anode outlet flow path 24 passes through a second heat exchanger 32 before proceeding to the first outlet 22. This second heat exchanger 32 is also disposed in the sweep gas supply flow path 18. The second heat exchanger 32 is disposed in the sweep gas supply flow path 18 between the first heat exchanger 30 and the anode inlet 14. Thus, the anode outlet flow path 24 and the sweep gas supply flow path 18 exchange heat in the second heat exchanger 32.

[0072] The anode outlet flow passage 24 can carry exhaust gas from the anode outlet 20. The exhaust gas from the anode outlet 20 can contain thermal energy. In particular, during operation of the system 10, the exhaust gas can contain high-grade heat (e.g., about 550° C.). Thus, the heat from the exhaust gas can be utilized to heat the sweep gas supply flow passage 18 in the second heat exchanger 32. This is beneficial for supplying a sweep gas to the anode inlet 14 at a high temperature to enhance the efficiency of the electrolysis reaction in the stack 12.

[0073] The sweep gas supply passage 18 is provided with a first heater 34. It is positioned between the second heat exchanger 32 and the anode inlet 14. The first heater 34 is used to increase the temperature of the sweep gas supply source 16 in the sweep gas supply passage 18. The first heater 34 may be an electric heater or a combustion heater, as required. The first heater 34 further heats the sweep gas supply passage 18, as required. It may be referred to as an inlet heater or a sweep gas heater.

[0074] In situations where the heat transfer capacity in the first and second heat exchangers 30, 32 is high, a smaller amount of heat energy can be provided in the first heater 34. On the other hand, when the heat transfer capacity in the first and second heat exchangers 30, 32 is low, a larger amount of heat energy can be provided in the first heater 34. This can be beneficial during start-up when the system 10 is not generating much heat energy in the electrolysis reactions in the electrolysis stack 12.

[0075] The first heater 34 is also referred to as a trim heater because it provides a small amount of heat to fine-tune the temperature at the anode inlet 14 to ensure a consistent and efficient electrolyzer reaction in the stack 12 .

[0076] The bypass flow path 36 is shown connected to the sweep gas supply flow path 18. The bypass flow path 36 is connected at a first end 38 to a point on the sweep gas supply flow path 18 between the sweep gas supply 16 and the first heat exchanger 30. The first end 38 is therefore upstream of the first heat exchanger 30. The bypass flow path 36 is connected at a second end 40 to a point between the second heat exchanger 32 and the first heater 34. The second end is therefore downstream of the second heat exchanger 32.

[0077] The bypass flow path 36 bypasses the first and second heat exchangers 30, 32, allowing the sweep gas supply flow path 18 to avoid exchanging heat with the heat exchangers. This may be beneficial when the thermal energy in the external flow path 28 and / or the anode outlet flow path 24 is at a level that is not needed for the sweep gas supply flow path 18. Such situations may include during start-up, when the flow paths may be cold, or during cool-down, when the transfer of heat to the sweep gas supply flow path 18 is no longer needed and the sweep gas supply 16 is being used to cool the system 10.

[0078] The bypass flow path 36 can be operated by a control valve or the like. The control valve can be a mechanical or electrical control valve set to a particular setting to open or close, or can be manually operated. A controller, i.e., a controller including a processor and memory, can be programmed to operate the control valve as needed in particular situations.

[0079] While the above is presented as shown in Figure 1, it is emphasized that certain variations are possible. In particular, the presence or absence of the first heat exchanger 30, the second heat exchanger 32, the first heater 34, and the bypass flow path 36 can be modified as necessary to the functionality of the system 10. In some circumstances, such as when the external fluid stream 26 is high grade heat, the second heat exchanger 32 may not be required.

[0080] A fuel supply 42 is provided and connected to a cathode inlet 44 provided in the electrolysis stack 12. The cathode inlet 44 is the inlet to the cathode of the electrolysis stack 12. Connecting therebetween is a fuel supply passage 56, which forms a fuel flow, pipe or line that enters the system 10 at the fuel supply 42 and leads to the cathode inlet 56.

[0081] The electrolysis stack 12 further comprises a cathode outlet 48 which is an outlet from the cathode of the electrolysis stack 12. The cathode outlet 48 is connected to the second exhaust 46 by a cathode outlet passage 54.

[0082] The electrolyzer reaction in the stack 12 requires fuel, which is provided in a fuel source 42 and delivered to the electrolysis stack 12 at the cathode inlet 44. The fuel is typically water or steam and it is at the cathode that the product of the reaction, typically hydrogen, is produced. Thus, it is hydrogen that is output at the cathode outlet 48 and delivered via the cathode outlet flow path 54 to the second outlet 46. The output of the second outlet 46 is captured for use in the required process.

[0083] 1, a third heat exchanger 50 is provided in the fuel supply passage 56 between the fuel supply source 42 and the cathode inlet 44. Furthermore, the cathode outlet passage 54 is connected to the third heat exchanger 50 between the cathode outlet 48 and the second outlet 46 of the cathode outlet passage 54. Thus, heat exchange occurs between the cathode outlet passage 54 and the fuel supply passage 42.

[0084] This thermal energy can then be utilized to heat the fuel supply channel 56. This can be beneficial since it is preferred to use steam for the electrolyzer reaction and therefore the fuel has high thermal energy. Thus, in the third heat exchanger 50, thermal energy can be transferred from the cathode outlet channel 54 to the fuel supply channel 56. This heat exchanger 50 can be referred to as a recuperative heat exchanger.

[0085] This can also be beneficial because the product (e.g., hydrogen) at the second outlet 46 preferably has lower thermal energy for delivery to other processes, and therefore the transfer of heat from the product is beneficial.

[0086] The fuel supply passage 56 is provided with a second heater 52 for heating the passage. The second heater 52 is positioned between the third heat exchanger 50 and the cathode inlet 44. The second heater 52 is therefore downstream of the fuel inlet 42. The second heater 52 is similar to the first heater 34 in that it may be an electric heater or a combustion heater, as desired. The second heater 52 provides additional heating to the fuel supply passage 56, as desired.

[0087] In situations where the heat transfer capacity in the third heat exchanger 50 is high, a lower amount of thermal energy can be provided in the second heater 52. On the other hand, when the heat transfer capacity in the third heat exchanger 50 is low, a higher amount of thermal energy can be provided in the second heater 52. This can be beneficial during start-up when the system 10 is not producing much thermal energy in the electrolyzer reactions in the electrolysis stack 12.

[0088] The second heater 52 is also referred to as a trim heater for the same reasons as the first heater 34, as it provides a small amount of heat to fine-tune the temperature at the cathode inlet 44 to ensure a consistent and efficient electrolyzer reaction in the stack 12.

[0089] The addition of the third heat exchanger 50 and second heater 52 is optional, and each of these may vary depending on other components such as the first heat exchanger 30, the second heat exchanger 32, the first heater 34, and the bypass flow path 36, as needed for the desired functionality and efficiency of the system 10.

[0090] Referring to Figure 2, there is shown an electrolyser system 10 as shown in Figure 1, except that the anode outlet flow passage 24 is provided with a third heater 58. The third heater 58 is positioned in the anode outlet flow passage 24 between the anode outlet 20 and the second heat exchanger 32.

[0091] The third heater 58 is an electric or fired heater provided to heat the anode exhaust gas in the anode outlet passage 24. This can be useful to provide additional heating for the sweep gas supply passage 18, such as when the anode exhaust gas has low grade heat (e.g., during start-up or warm-up).

[0092] The third heater 58 can further heat the anode outlet flow passage 24 between the anode outlet 20 and the third heater 58. This can be accomplished by a counterflow through the anode outlet flow passage 24. The counterflow can be provided, for example, from the external fluid stream 26. Thus, the external flow passage 28 can be heated by the third heater 58. Heating the anode outlet flow passage 24 using a counterflow to the anode outlet 20 can be useful for heating the system 10 and stack 12 during start-up and prior to operation.

[0093] During full operation, when the anode exhaust gas at the anode outlet 20 is hot, the third heater 58 may not be needed, thereby reducing the need to heat the anode outlet flowpath 24 by the third heater 58. The third heater 58 may also be controlled to provide variable heating to the anode outlet flowpath 24 as needed.

[0094] Referring to Figure 3, there is shown an electrolyser system 10 as shown in Figure 1, except that in Figure 3 the location of the first heat exchanger 30 is reversed from the location of the second heat exchanger 32. That is, the second heat exchanger 32 is positioned upstream of the first heat exchanger 30, the second heat exchanger is positioned between the sweep gas inlet 16 and the first heat exchanger 30, and the first heat exchanger is positioned between the second heat exchanger 32 and the anode inlet 14. The connections to each heat exchanger remain the same, i.e. the external flow path 28 from the external fluid stream 26 remains in fluid connection with the first heat exchanger 30. Similarly, the anode outlet flow path 24 from the anode outlet 20 to the first outlet 22 is in fluid communication with the second heat exchanger 32.

[0095] The reordering of the first and second heat exchangers 30, 32 allows for a situation where heat exchange with the anode exhaust gas and sweep gas source 16 is preferred followed by heat exchange with the external fluid stream 26 and sweep gas source 16. This can be beneficial when the external fluid stream 26 is, for example, high grade heat.

[0096] Referring to Figure 4, there is shown an electrolyser system 10 as shown in Figure 1. In Figure 4, a fourth heat exchanger 60 is provided in the fuel supply flow path 56. The fourth heat exchanger 60 is positioned downstream of the third heat exchanger 50, i.e. between the third heat exchanger 50 and the cathode inlet 44, or between the third heat exchanger 50 and the second heater 52, if the second heater 52 is provided.

[0097] The fourth heat exchanger 60 is further in fluid contact with a second external flow path 64. The second external flow path 64 is a flow path that is generated separately from the process of the electrolyzer system 10. The second external flow path 64 is formed from a second external fluid stream 62 from a source that is external to the system 10. Although the external fluid stream 26 and the second external fluid stream 62 are shown as separate, these streams may be the same. In such a case, the splitting of the streams may occur within the electrolyzer system 10 or outside the system 10.

[0098] The second external flow path 64 exchanges heat with the fuel supply flow path 56 via the fourth heat exchanger 60. If the second external fluid stream 62 contains thermal energy, it can be transferred into the fourth heat exchanger 60 to supply heat to the fuel supply flow path 56 for feeding into the electrolysis stack 12 through the cathode inlet 44. The hotter fuel can support the electrolyzer reaction. This can be beneficial during start-up when the products in the cathode outlet flow path 54 have no or low thermal energy and therefore are not as effective as being used to recover heat through the third heat exchanger 50.

[0099] Referring to Figure 5, there is shown an electrolyser system 10 as shown in Figure 4, except that in Figure 5 the location of the fourth heat exchanger 60 is reversed from the third heat exchanger 50. Thus, the fourth heat exchanger 60 is upstream of the third heat exchanger 50 in the fuel supply flow path 56, and the fourth heat exchanger 60 is between the fuel supply 42 and the third heat exchanger 50. Similarly, the third heat exchanger is between the fourth heat exchanger 60 and the cathode inlet 44 (or the second heater 52, if provided) in the fuel supply flow path 56.

[0100] The fluid connections of the heat exchangers remain the same, i.e. the fourth heat exchanger 60 is connected to the second external flow passage 64 for exchanging heat between the second external flow passage 64 and the fuel supply flow passage 56. Similarly, the third heat exchanger 50 is connected to the cathode outlet flow passage 54 for exchanging heat between the cathode outlet flow passage 54 and the fuel supply flow passage 56.

[0101] Reversing the third and fourth heat exchangers 50, 60 allows the second external fluid stream 62 to be fed into the fuel supply passage 56 before the heat from the cathode outlet passage 54. This may be beneficial when the second external fluid stream 62 has lower grade heat and it is desirable to exchange this heat before the higher grade heat from the cathode outlet 48 to reduce temperature exchange in each of the heat exchangers.

[0102] Referring to Figure 6, there is shown an electrolyser system 10 as shown in Figure 2, where a third heater 58 in the anode outlet flow passage 24 is provided.

[0103] 6, a switching valve 66 is provided that is positioned in the anode outlet flowpath 24 and configured to switch flow through the various ports. The switching valve 66 is positioned between the anode outlet 20 and the second heat exchanger 32. More specifically, if the third heater 58 is present, the switching valve 66 is positioned in the anode outlet flowpath 24 between the anode outlet 20 and the third heater 58.

[0104] The diverter valve 66 has a further connection to the external flow path 28. Thus, the diverter valve 66 can switch flow between a stack section 72 of the anode outlet flow path 24, a burner section 74 of the anode outlet flow path 24, and the external flow path 28.

[0105] While many means can be used to connect the external flow path 28 to the diverter valve 66, in one embodiment, a branch line 70 (branch flow path) can be used. The branch line 70 connects from the external flow path 28 directly to the diverter valve 66. The branch line 70 may also be referred to as an external flow path, a branch pipe, an extension, or a duct.

[0106] The diverter valve 66 may further be connected to another connection, which is a third outlet 68. This allows flow through the diverter valve 66 to also be directed to a third outlet 68, which may generally be located away from other components and external to the system 10.

[0107] The diverter valve 66 can be utilized in a number of ways depending on the operation required: (i) During normal operation of the system 10, such as when the stack 12 is warmed up and operating at base load, the diverter valve 66 connects the stack section 72 and the burner section 74 of the anode outlet flowpath 24 to form a connection between the anode outlet 20 and the second heat exchanger 32. This is beneficial during normal operation because the hot anode exhaust gas can be used to heat the sweep gas supply in the second heat exchanger 32, thus acting as a recuperator.

[0108] The third heater 58 in this configuration may further be used to supply additional thermal energy to the anode outlet flow passage 24 for use in a second heat exchanger, such as during a warm-up phase, or for heating the backflow to the anode outlet 20 to warm the stack 12.

[0109] (ii) In warm-up operation, the diverter valve 66 can connect the branch line 70 to the stack portion 72 of the anode outlet flowpath 24. This can use heat from the external fluid stream 26 to heat the anode outlet 20 and the anode outlet flowpath 24, including the stack 12.

[0110] Additionally or alternatively, the diverter valve 66 can connect the branch line 70 to a burner section 74 of the anode outlet flowpath 24. This allows hot flow from the external fluid stream 26 to pass through both heat exchangers to warm the sweep gas supply flowpath 18, such as during start-up or warm-up. This mode can also use heat from the third heater 58 to heat the external fluid stream 26 to provide a counterflow for heating the stack section 72 of the anode outlet flowpath 24.

[0111] (iii) In the cool-down operation, the switching valve 66 can connect the stack section 72 of the anode outlet flow path 24 to the third exhaust port 68. This allows the anode exhaust gas from the anode outlet 20 to be discharged through the third exhaust port 68 without heat exchange in the second heat exchanger 32.

[0112] Such an operating mode may be beneficial when the electrolysis stack 12 is cooled down so that heat recovery in the second heat exchanger 32 is no longer required. This mode can also be operated when the temperature of the exhaust gas from the anode outlet 20 exceeds the thermal limits of the components, such as during full operation.

[0113] Although the diverter valve 66 is shown with four connection ports, it will be understood that the diverter valve 66 may be configured in many ways to allow one or more connections as needed. The diverter valve 66 may be a mechanical or electrically controlled valve set to a particular value to switch the flow in the required direction, or may be manually operated. In some circumstances, a controller, i.e., a controller including a processor and memory, is programmable to operate the diverter valve 66 as needed.

[0114] Referring to Figure 7, an electrolyzer system 10 as shown in Figure 1 and described above is shown, combining features of the other figures. For example, as mentioned above, the external fluid stream 26 and the second external fluid stream 62 may be from the same source. Here, it is shown that the external fluid streams 26, 62 are supplied from the same source and then split into an external flow path 28 for connection to the first heat exchanger 30 and a second external flow path 64 for connection to the fourth heat exchanger 60. Thus, the first and fourth heat exchangers 30, 60 use the same heat source for heat transfer with the sweep gas supply and the fuel supply, respectively.

[0115] A third heater 58 is also shown in Figure 7. However, a burner fuel supply line 80 is provided which may supply fuel to the third heater 58 using a combustion burner or the like. It will be appreciated that the third heater 58 only needs to operate the burner fuel supply line 80 during operation when the anode exhaust gas is cold. The supply line may also be referred to as the burner fuel supply passage.

[0116] The cathode outlet flow passage 54 is provided with a cathode outlet branch flow passage 76 (branch flow passage 76) between the anode outlet 48 and the second exhaust port 46. The branch flow passage 76 is connected to the anode outlet flow passage 24 between the anode outlet 20 and the third heater 58. Thus, the branch flow passage 76 can supply a product (e.g., hydrogen gas) to the anode outlet flow passage 24. This branch flow passage 76 makes it possible to supply the product from the cathode outlet 48 to the third heater 58. Therefore, the third heater 58 can use the direct product of the electrolysis stack 12 without using a burner fuel supply line 80.

[0117] The inclusion of a third heater 58 downstream of the stack 12 allows products (e.g., hydrogen) to be bled off the cathode exit passage 54 to raise the sweep gas supply temperature in the second heat exchanger 32 without the need for electrical heating. During start-up of the system 10, a dedicated hydrogen flow or other combustible fuel flow can be supplied from a burner fuel supply line 80.

[0118] A bleed valve 78 is provided in the branch flow path 76 to control the flow of product from the cathode outlet flow path 54 to the third heater 58 according to the requirements of the system 10. The bleed valve 78 may be a mechanical or electrically controlled valve set to a specific value to switch the flow in the required direction, or may be manually operated. In some circumstances, a controller, i.e., a controller including a processor and memory, is programmable to operate the bleed valve 78 as needed.

[0119] The branch flow path 76 may be positioned anywhere along the cathode outlet flow path 54, either before, i.e., upstream, of the third heat exchanger 50, or between the third heat exchanger 50 and the second exhaust 46, i.e., downstream of the third heat exchanger 50. The products do not need to be hot if they are combusted in the third heater 58. Therefore, it may be preferable to exchange heat before the branch flow path.

[0120] Overall, the electrolyzer system design improves the use of heat recovery and heat exchange during start-up, normal operation, and cool-down to enable more efficient reactions in the electrolysis stack, and efficient use of otherwise unused heat from the process.

[0121] The present invention is not limited to only the above-described embodiments, and other embodiments will be readily apparent to those skilled in the art without departing from the scope of the appended claims. [Explanation of symbols]

[0122] 10 Electrolyzer System 12 Electrolytic Stack 14 Anode inlet 16 Sweep gas supply source 18 Sweep gas supply passage 20 Anode outlet 22 First outlet 24 Anode outlet flow path 26 External Fluid Flow 28 External flow path 30 First heat exchanger 32 Second heat exchanger 34 First heater 36 Bypass flow path 38 First end of bypass flow path 40 second end of bypass flow path 42 Fuel supply source 44 Cathode inlet 46 Second outlet 48 Cathode outlet 50 Third Heat Exchanger 52 Second Heater 54 Cathode outlet flow path 56 Fuel supply passage 58 Third Heater 60 Fourth Heat Exchanger 62 Second external fluid flow 64 Second external flow path 66 Switching valve 68 Third Outlet 70 Branch Line 72 (Anode outlet flow path) stack section 74 (Anode outlet passage) burner section 76 Cathode outlet branch flow channel 78 Bleed valve 80 Burner fuel supply line

Claims

1. A solid oxide electrolyzer cell system, An electrolysis stack comprising an anode, a cathode, and a solid oxide electrolyte, wherein the anode has an anode inlet, the electrolysis stack; A sweep gas supply source for supplying a sweep gas to the anode through the anode inlet; A sweep gas supply flow path defining a flow path between the sweep gas supply source and the anode inlet; And a first heat exchanger in fluid communication with the sweep gas supply flow path. The first heat exchanger has a supply source outside the solid oxide electrolyzer cell system and is also in fluid communication with a fluid flow defining an external flow path. The first heat exchanger is configured to exchange heat between the sweep gas supply flow path and the external flow path, the solid oxide electrolyzer cell system.

2. A bypass flow path connected to the sweep gas supply flow path, which is connected at its first end to a position upstream of the first heat exchanger and at its second end to a position downstream of the first heat exchanger. The solid oxide electrolyzer cell system according to claim 1, further comprising a bypass flow path.

3. The solid oxide electrolyzer cell system according to claim 1, further comprising a first heater positioned within the sweep gas supply flow path and connected downstream of the first heat exchanger.

4. An anode outlet for the anode of the electrolysis stack, comprising an anode outlet flow path defining a flow path between the anode outlet and a first discharge outlet, the anode outlet; A second heat exchanger in fluid communication with the sweep gas supply flow path and positioned downstream of the first heat exchanger in the sweep gas supply flow path, the second heat exchanger being also in fluid communication with the anode outlet flow path and configured to exchange heat between the sweep gas supply flow path and the anode outlet flow path. The solid oxide electrolyzer cell system according to any one of claims 1 to 3, further comprising.

5. A cathode inlet for the cathode of the electrolysis stack; A fuel supply source for supplying fuel to the cathode through the cathode inlet; A fuel supply flow path defining a flow path between the fuel supply source and the cathode inlet; A cathode outlet for the cathode of the electrolysis stack; A cathode outlet flow path defining a flow path between the cathode outlet and a second discharge outlet; A third heat exchanger that is in fluid communication with the downstream side of the fuel supply flow path, is also in fluid communication with the cathode outlet flow path, and is configured to exchange heat between the fuel supply flow path and the cathode outlet flow path. The solid oxide electrolysis cell system according to claim 4, further comprising the same. **Claim 6** The solid oxide electrolysis cell system according to claim 5, further comprising a cathode outlet branch flow path that connects the cathode outlet flow path and the anode outlet flow path to put them in fluid communication. **Claim 7** The solid oxide electrolysis cell system according to claim 6, further comprising a valve disposed in the cathode outlet branch flow path. **Claim 8** The solid oxide electrolysis cell system according to claim 4, further comprising a fourth heat exchanger that is in fluid communication with the fuel supply flow path, is also in fluid communication with the external flow path, and is configured to exchange heat between the flow paths. **Claim 9** In the solid oxide electrolysis cell system according to claim 8, the third heat exchanger is in fluid communication with the fuel supply flow path downstream of the fourth heat exchanger. **Claim 10** The solid oxide electrolysis cell system according to claim 5, further comprising a second heater positioned in the fuel supply flow path disposed downstream of the third heat exchanger. **Claim 11** The solid oxide electrolysis cell system according to claim 4, further comprising a third heater positioned in the anode outlet flow path between the anode outlet and the second heat exchanger. **Claim 12** The solid oxide electrolysis cell system according to claim 4, further comprising a switching valve connected to the anode outlet flow path at a position between the anode outlet and the second heat exchanger. The switching valve is also connected to the external flow path and a third discharge port, and the switching valve is configured to direct the flow between at least one of the anode outlet and the second heat exchanger, the external flow path, or the third discharge port. **Claim 13** A method of operating a solid oxide electrolysis cell system, comprising: providing a sweep gas supply source for supplying a sweep gas to the anode of the electrolysis stack through the anode inlet, and defining a sweep gas supply flow path between the sweep gas supply source and the anode inlet; forming a fluid flow having a supply source outside the solid oxide electrolysis cell system, and defining an external flow path from the fluid flow. Performing heat exchange between the external flow path and the sweep gas supply flow path via the first heat exchanger An operation method including this.

14. The operation method of the solid oxide electrolytic cell system according to claim 13, wherein an anode outlet flow path is defined between the anode outlet of the anode of the electrolytic cell and the first discharge port to the system.

15. The operation method of the solid oxide electrolytic cell system according to claim 14, including performing heat exchange between the anode outlet flow path and the sweep gas supply flow path by a second heat exchanger disposed in the sweep gas supply flow path at a position downstream of the first heat exchanger.

16. The operation method of the solid oxide electrolytic cell system according to claim 15, including bypassing the first heat exchanger and the second heat exchanger by a bypass flow path disposed in the sweep gas supply flow path upstream of the first heat exchanger and downstream of the second heat exchanger.

17. The operation method of the solid oxide electrolytic cell system according to claim 15 or claim 16, including supplying heat to the anode outlet flow path from a third heater disposed in the anode outlet flow path between the anode outlet and the second heat exchanger.

18. The operation method of the solid oxide electrolytic cell system according to claim 17, including supplying heat to the anode outlet flow path from the external fluid flow path or the third heater by a switching valve disposed in the flow path between the anode outlet and the burner.

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