Electrolyzer systems for intermittent electricity supply

Abstract

The present invention provides an electrolyzer system (10) comprising a thermal storage unit (14) and an electrolyzer (16). The thermal storage unit (14) comprises at least one heat source inlet. The electrolyzer (16) comprises at least one electrolytic cell (20), a steam inlet, and at least one exhaust gas outlet. The exhaust gas outlet is connected to the heat source inlet and heats the thermal storage unit (14). The thermal storage unit (14) is configured to use stored heat to generate steam for supplying the steam inlet and for generating electrical power, either one at a time or both simultaneously. The present invention also provides a system comprising an intermittent or variable electrical source (12) and the electrolyzer system (10) defined above. The intermittent or variable electrical source (12) can be configured to power the electrolyzer (16) and heat the thermal storage unit (14) via a heating element, either simultaneously or separately.

Description

[Technical Field]

[0001] The present invention relates to an electrolyzer system, preferably a solid oxide electrolyzer system, configured to accommodate intermittent or variable electricity sources, such as typical renewable power sources, including but not limited to hydro, tidal, solar, wind, or wave power. [Background technology]

[0002] Due to the intermittent or fluctuating nature of the power source in the case of intermittent electrical sources, for example due to lack of daylight at night in the case of solar power, or due to periods of stillness in the case of wind or wave power, or due to slow cycles of the tides in the case of tidal power, or due to periods of drought in the case of hydropower, fluctuations, decreases, or declines can occur in the power output from such electrical sources.

[0003] Electricity on the grid may also be considered an intermittent or variable source of electricity, for example, if it prioritizes other electricity users (e.g., homes, hospitals, etc.) by limiting or cutting off supply to industrial users (e.g., electrolyzers) during periods of high demand. Similarly, an electricity grid may be considered intermittent or variable if demand periodically exceeds supply and inadequate and / or unreliable infrastructure results in "blackouts" or power disruptions / supply problems.

[0004] As a result, if these energy sources provide electricity to power an electrolyzer (e.g., to extract hydrogen and oxygen from water), the electrolyzer device will need to shut down if there is no alternative power source to keep the electrolyzer device running.

[0005] For certain electrolysis cells, particularly medium- to high-temperature electrolysis cells, especially those with operating temperatures above 400°C (e.g., SOECs), such downtime can result in extended periods of inoperability and reduced power output efficiency. This is because many electrolysis cell configurations have extended start-up procedures to protect or start-up the electrolysis cell components. For example, SOECs typically do not function below 400°C, and to achieve optimal efficiency, some SOEC designs require operating temperatures above the temperature at which electrolysis begins (e.g., 450°C or 500°C). Therefore, maintaining power to such electrolysis devices is necessary to ensure optimal efficiency or to enable continuous operation.

[0006] Also, in some electrolysis devices, due to the large difference between their operating temperature and the ambient temperature, it is important to maintain their power supply long enough to perform appropriate shutdown procedures to protect their components, particularly their electrochemically active components.

[0007] It would therefore be useful to be able to compensate for such declines in power from intermittent or variable electrical sources, such as typical renewable power sources, including but not limited to solar, wind, tidal, hydro, and wave power.

[0008] Typically, this is done by providing a variety of power sources, for example, by using a combination of solar and wind power or other alternative energy sources such as tidal, wave, or hydropower, or by supplementing the power supply with more traditional "on-demand" sources such as gas, coal, wood pellets, geothermal, or nuclear power. Another approach is to store natural sources of power, such as reservoirs for hydropower. However, in the case of solar and wind power, an acceptable approach is to use energy storage devices such as batteries (most commonly lithium-ion batteries due to their acceptable storage capacity per unit weight). However, because lithium for such batteries is a scarce resource and its mining and refining is energy and carbon intensive, additional approaches to smooth out power declines would be beneficial. Summary of the Invention [Means for solving the problem]

[0009] According to a first aspect of the present invention, there is provided an electrolyzer system comprising: a thermal storage unit; an electrolytic cell; the thermal storage unit includes at least one heat source inlet; the electrolyzer comprises at least one electrolysis cell, a steam inlet, and at least one exhaust gas outlet, the exhaust gas outlet being connected to the heat source inlet for heating the thermal storage unit; An electrolyzer system is provided in which the heat storage unit is configured to use its stored heat to generate steam for supplying the steam inlet and steam for generating electrical power, either at a time or both simultaneously. This configuration allows waste heat generated as a result of the electrolysis reaction in the electrolyzer, or generated elsewhere, such as from an external industrial process in a nearby industrial facility, to be stored in the heat storage unit and reused selectively to generate steam and / or to generate electrical power, either both simultaneously or separately. This allows for leveling of steam and / or electricity supply when required by the electrolyzer due to, for example, fluctuations in the electricity supply, or for supplying electricity to external equipment or the power grid when not required by the electrolyzer.

[0010] Typically, at least one electrolysis cell is part of a stack of electrolysis cells.

[0011] Alternatively, each electrolysis cell may include an anode, a cathode, and an electrolyte. Some stacks may additionally include dummy cells, as known in the art, to improve temperature distribution to the active electrolysis cells within the stack.

[0012] In some embodiments, heat from the thermal storage unit can be selectively used to generate hot air to supply the electrolyzer or external equipment. This can be in addition to steam and electricity (e.g. via a steam cycle / turbine). The present invention can compensate for variations in the supply to the electrolyzer, specifically: a) heat (to maintain the desired operating temperature of the electrolytic cell) - as steam or hot air or both are supplied to the electrolyzer, and b) electricity - to at least partially power the electrolyzer when needed due to variations in its normal power supply.

[0013] Thus, in some embodiments, at least a portion of the generated electrical output is selectively provided to the electrolysis cell, configured to at least partially power the electrolyzer. For example, in some embodiments, the electrolyzer system is configured to selectively connect at least a portion of the electrical output generated by the electrolyzer system to the electrolyzer, such that the electrolyzer can be selectively powered, at least in part, by the generated electrical output, thereby compensating for intermittencies in its normal power source, such as from alternative energy sources such as typical renewable power sources, including but not limited to solar, wind, wave, etc.

[0014] In some embodiments, the thermal storage unit comprises a hot air (or nitrogen) outlet. In some embodiments, the electrolyzer comprises a hot air (or nitrogen) inlet.

[0015] In some embodiments, the hot air outlet of the thermal storage unit is connected to the hot air inlet of the electrolyzer, allowing hot air (or nitrogen) to be selectively supplied to the electrolyzer while the electrolyzer system is in use.

[0016] The input gases to the electrolyzer are usually only steam (or water) and air (or nitrogen).

[0017] According to the present invention, the hot air stream can selectively exit from the hot air (or nitrogen) outlet of the thermal storage unit and be supplied to the electrolyzer or additionally / alternatively to external equipment requiring the hot air (or nitrogen) or its heat.

[0018] In some embodiments, the thermal storage unit comprises a steam outlet such that, during use of the thermal storage unit, a steam stream can selectively exit through the steam outlet and be supplied to an electrolysis cell / electrolyzer or a steam turbine, or alternative external equipment requiring steam (or its heat).

[0019] In some embodiments, the system comprises a steam supply line for supplying steam to the steam inlet of the electrolyzer from the thermal storage unit or from a steam turbine connected to the thermal storage unit.

[0020] In some embodiments, a steam supply line connects between the thermal storage unit and the steam turbine and between the steam turbine and the steam inlet, and in some embodiments may have a bypass for selectively bypassing the steam turbine.

[0021] In some embodiments, the heat from the thermal storage unit is configured to power a steam cycle to generate electricity (electrical output) for external distribution (e.g., to a power grid or distribution to external devices) or to at least partially power the electrolyzer. The steam cycle can occur within or outside the thermal storage unit.

[0022] In some embodiments, the system further comprises a steam turbine for selectively producing electrical output using heat or steam from the thermal storage unit.

[0023] In some embodiments, the thermal storage unit includes a water inlet and / or an air inlet, which may be for replenishing or adding water and / or air to the thermal storage unit. For example, water may be provided for conversion to steam, and air may be provided for preheating before being supplied to the electrolyzer as a sweep stream to the anode side.

[0024] In some embodiments, the thermal storage unit is configured to evaporate water within the thermal storage unit to produce steam that can be used for external applications. Water can be supplied to the thermal storage unit via a water inlet.

[0025] In some embodiments, the exhaust gas outlet is connected to the heat source inlet of the thermal storage unit via a supply pipe.

[0026] The electrolyzer system may be configured to receive steam or water from one or more external industrial systems at a steam inlet of the electrolyzer. Such steam or water supply may be intermittent, and therefore, to compensate for the intermittency of the steam supply to the electrolyzer, additional steam may be supplied from a thermal storage unit or a steam cycle connected thereto.

[0027] Since high pressure steam can damage elements of the electrolyzer system, in particular the electrolyzer or electrolysis cells, or some external equipment, the electrolyzer system is preferably configured to supply steam to the steam inlet of the electrolyzer at a pressure lower than the steam pressure to the steam turbine. In some embodiments, a steam cycle (typically the steam turbine) is used to reduce the pressure of the steam from the pressure at which it is supplied to the steam cycle or turbine to the supply pressure at which it leaves the steam cycle or turbine for supply to the steam inlet of the electrolyzer (or external equipment).

[0028] The steam generated by the heat of the thermal storage unit can potentially be superheated steam at temperatures above 400°C. Passing superheated steam through a steam cycle (or steam turbine) can damage components of that equipment. However, the steam entering the steam inlet of the electrolyzer needs to be at a very high temperature (e.g. above 400°C) to maintain the desired temperature of the electrolyzer and therefore the efficiency of the electrolyzer. Therefore, in some embodiments, the electrolyzer system comprises a steam cycle or a steam turbine.

[0029] Furthermore, in some embodiments, the electrolyzer system also comprises a regenerative heat exchanger, which is advantageously arranged to exchange heat between the outlet of the steam cycle or steam turbine and the steam inlet of the electrolyzer. In some embodiments, a regenerative heat exchanger is arranged both between the thermal storage unit and the steam cycle or steam turbine, and between the steam cycle or steam turbine and the steam inlet of the electrolyzer. Such a regenerative heat exchanger is therefore configured to cool the steam before it enters the steam cycle or steam turbine, and to reheat the steam after it leaves the steam cycle or steam turbine but before it reaches the steam inlet of the electrolyzer.

[0030] In some embodiments, the electrolyzer system comprises a control system that controls the distribution of steam within the system, the control system being configured to selectively supply steam to the steam cycle or steam turbine, or to a steam inlet of the electrolyzer, or both.

[0031] In some embodiments, the or each electrolysis cell has an operating stack temperature above 400°C.

[0032] In some embodiments, at least one electrolysis cell is a solid oxide electrolysis cell, i.e., the electrochemically active region is a solid oxide. Solid oxide electrolysis cells (SOECs) typically operate in the temperature range of 400-650°C, or more specifically, 520-620°C. Such electrolysis cells are sometimes referred to as intermediate-temperature solid oxide electrolysis cells, or IT-SOECs.

[0033] There are many possible configurations of SOECs that use different electrochemically active electrolyte chemistries, for example, three well-known electrolyte materials are yttria-stabilized zirconia (YSZ), scandium-stabilized zirconia (ScSZ), and gadolinium-doped ceramic (GDC or CGO).

[0034] Ideally, the or each electrolysis cell is an intermediate temperature solid oxide electrolysis cell or IT-SOEC with an operating stack temperature between 400° C. and 700° C. However, in some embodiments, the electrolysis cell system comprises a high temperature electrolysis cell with an operating stack temperature between 700° C. and 1100° C.

[0035] In some embodiments, the thermal storage unit is a molten salt technology unit, which may use various eutectic mixtures of different salts (e.g., sodium nitrate, potassium nitrate, and / or calcium nitrate).

[0036] In some embodiments, the thermal storage unit is a latent heat storage unit, a thermochemical heat storage unit, a hot silicon technology unit, a steam accumulation unit, or a molten aluminum technology unit (such as those offered by Azelio®).

[0037] In some embodiments, the electrolyzer system includes connections for connection to an intermittent or variable electricity source. An intermittent or variable electricity source is one that experiences "blackouts" or power disruptions or supply continuity issues due to a lack of infrastructure and / or unreliability, and is not simply an alternating current electricity source (i.e., not simply AC power). For example, intermittent does not necessarily mean "dropping to zero," but rather refers to the intermittent drop in available supply below a required or target threshold for operation, resulting in a sub-optimal or insufficient supply.

[0038] In some embodiments, the heat storage unit is connected to an external heat source in order to increase the amount of heat stored therein, thereby increasing the compensation for downtime of the electrolyzer's electrical supply.

[0039] The present invention also provides a system comprising an intermittent or variable electricity source and an electrolyzer system as defined above, which system may be configured to utilise excess heat stored in a thermal storage unit to compensate for fluctuations or reductions in electrical power from the intermittent or variable electricity source, which may be achieved by selectively powering a steam turbine to generate an electrical output to at least partially power the electrolyzer.

[0040] In some embodiments, an intermittent or fluctuating electrical source is configured to power the electrolyzer and to heat the thermal storage unit via a heating element, either simultaneously or separately.

[0041] In some embodiments, the intermittent or fluctuating electrical source is configured to power the electrolyzer, to heat or generate steam for the stack, and / or to generate hot air for the stack, either both simultaneously or separately.

[0042] The present invention also provides a method of operating an electrolytic cell system, the electrolytic cell system comprising: a thermal storage unit; an electrolytic cell; the thermal storage unit includes at least one heat source inlet; the electrolyzer comprises at least one electrolysis cell, a steam inlet, and at least one exhaust gas outlet, the exhaust gas outlet being connected to the heat source inlet; The method is: heating a thermal storage unit using exhaust gas from the exhaust gas outlet; using heat stored in the thermal storage unit to generate steam for supplying to the steam inlet and steam for generating electrical power, either one at a time or both at the same time; A method is provided that includes:

[0043] In a preferred aspect, the present invention provides a method for operating an electrolytic cell system or an electrical power supply system as defined above.

[0044] In some embodiments, the method comprises supplying additional heat to the thermal storage unit from one or more external industrial processes. This method allows waste heat generated as a result of the electrolysis reaction in the electrolyzer or generated elsewhere, such as from an industrial plant, to be stored in the thermal storage unit and selectively reused, either simultaneously or separately, to generate steam and / or to generate electrical output. This allows, for example, to level the supply of steam and / or electricity to the electrolyzer when needed by the electrolyzer due to fluctuations in the intermittent supply of electricity, or to supply electricity to external equipment or the power grid when not needed by the electrolyzer.

[0045] In some embodiments, the method includes selectively using heat from the thermal storage unit to generate hot air for supply to the electrolyzer or external equipment.

[0046] In some embodiments, the method comprises using said stored heat to compensate for fluctuations in the supply to the electrolyzer, in particular fluctuations in at least one of a) heat when steam or hot air or both are supplied to the electrolyzer, and b) electricity.

[0047] The heat can be used at least in part to maintain a desired operating temperature of the electrolyzer, if desired. The electricity can be used at least in part to at least in part power the electrolyzer, if desired.

[0048] In some embodiments, the method includes selectively supplying at least a portion of the generated electrical output to an electrolysis cell to at least partially power the electrolysis cell.

[0049] In some embodiments, the hot air (or nitrogen) stream selectively exits a hot air (or nitrogen) outlet of the thermal storage unit and is supplied to the electrolyzer.

[0050] In some embodiments, the method includes controlling a stream of steam selectively exiting a steam outlet of the thermal storage unit to supply to each of an electrolyzer and a steam turbine for producing electrical power, either individually or simultaneously, and a control system may be provided for effecting this control.

[0051] In some embodiments, steam is selectively supplied to the steam inlet of the electrolyzer through a steam supply line from a thermal storage unit or from a steam turbine connected to the thermal storage unit.

[0052] In some embodiments, the heat from the thermal storage unit powers a steam cycle that generates electricity for external distribution to a power grid or external equipment, or for at least partially powering the electrolyzer.

[0053] In some embodiments, the thermal storage unit evaporates water within the thermal storage unit to produce steam.

[0054] In some embodiments, the exhaust gas outlet supplies exhaust gas from the electrolyzer, and the gas supply line supplies the exhaust gas through a heat source inlet of the thermal storage unit to heat the thermal storage unit.

[0055] In some embodiments, the exhaust gas is either hydrogen-rich steam and / or oxygen-rich air.

[0056] In some embodiments, the thermal storage unit has an outlet for the or their exhaust gases for further collection or distribution of the exhaust gases after passing through the thermal storage unit.

[0057] In some embodiments, the electrolyzer system receives steam from one or more external industrial processes at a steam inlet, and steam is selectively supplied to the steam inlet from a further heat storage unit or a steam cycle connected thereto to compensate for interruptions in the steam supply to the electrolyzer from the external industrial processes.

[0058] In some embodiments, the method comprises reducing the pressure of the steam from an inlet pressure when fed to the steam cycle or turbine to a delivery pressure when leaving the steam cycle or turbine. In some embodiments, the steam cycle or steam turbine of the electrolyzer system reduces the pressure of the steam from the pressure when fed to the steam cycle or turbine to a delivery pressure when leaving the steam cycle or turbine and delivers the reduced pressure to a steam inlet of the electrolyzer or to external equipment.

[0059] In some embodiments, the electrolyzer system comprises a steam cycle or a steam turbine.

[0060] In some embodiments, the electrolyzer system further comprises a regenerative heat exchanger, which exchanges heat between the outlet of the steam cycle or steam turbine and the steam inlet of the electrolyzer. The regenerative heat exchanger may be located between the thermal storage unit and the steam cycle or steam turbine, and between the steam cycle or steam turbine and the steam inlet of the electrolyzer, and the regenerative heat exchanger cools the steam before it enters the steam cycle or steam turbine and reheats the steam after it leaves the steam cycle or steam turbine and before it reaches the steam inlet of the electrolyzer.

[0061] In some embodiments, the method uses a control system to control the distribution of steam within the system, the control system selectively supplying steam to a steam cycle or steam turbine, or to a steam inlet of the electrolyzer, or both.

[0062] In some embodiments, the at least one electrolysis cell operates during the electrolysis process at an operating stack temperature between 400° C. and 700° C., preferably in the range of 400° C. and 650° C., or particularly in the temperature range of 520° C. and 620° C. However, in some embodiments, the at least one electrolysis cell operates at an operating stack temperature between 700° C. and 1100° C.

[0063] In some embodiments, the method includes connecting the electrolysis system to an intermittent or variable electricity source, and the electrical output generated using the stored heat of the thermal storage unit is used to compensate for power fluctuations of the intermittent or variable electricity source. The intermittent or variable electricity source may be one or more power sources, such as typical renewable electricity sources, including, but not limited to, solar, wind, wave, tidal, or hydroelectric power.

[0064] In some embodiments, the thermal storage unit is further connected to an external heat source that supplies heat to it and increases the amount of heat stored therein, thereby increasing the compensation for downtime of the electrolyzer's electrical supply.

[0065] The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0066] [Figure 1] 1 shows a schematic representation of a first embodiment of an electrolyzer system according to the invention; [Figure 2] 2 shows a schematic representation of a second embodiment of an electrolyzer system according to the invention; [Figure 3] 1 shows a schematic representation of a typical electrolysis cell for use as an electrolyzer in an electrolyzer system, where multiple electrolysis cells may be stacked into an electrolysis cell stack. DETAILED DESCRIPTION OF THE INVENTION

[0067] The present invention relates to coupling an electrolyzer to a heat storage device that can selectively supply steam and / or electricity to the electrolyzer when power for inputs such as steam and / or electricity is unavailable, variable, unreliable or scarce (e.g. due to intermittent or variable sources). Figures 1 and 2 show different system configurations for coupling a heat storage device with an electrolyzer to enable extended or continuous operation using an intermittent or variable electricity source.

[0068] Referring initially to Figure 1, an electrolyzer system 10 is shown. The system uses electricity generated by an intermittent or fluctuating electrical source 12 to power an electrolyzer 16 to produce hydrogen and oxygen from water. These gases exit the electrolyzer 16 at an elevated temperature (i.e., above ambient temperature (or greater than 20°C)). This is typically a temperature comparable to or slightly lower than the operating temperature of the electrolyzer. For electrolyzers using solid oxide electrolysis cells (also known as SOECs), this temperature can exceed 400°C.

[0069] The intermittent or variable electricity source may utilize an external power source, typically a renewable energy source such as a wind turbine 46 , solar panels 48 , or hydropower 50 .

[0070] The heat of the gases (also known as exhaust gases) leaving the electrolyzer can be used to heat the thermal storage unit 14 by directing or passing the gases through the thermal storage unit 14. The stored heat can be returned to the electrolyzer 16 as needed to maintain the operating temperature of the electrolyzer 16. For this purpose, the thermal storage unit can be provided with a steam outlet 34 and a hot air outlet 30, which can be connected to the steam inlet 22 and hot air inlet 32 ​​of the electrolyzer 16 via a steam supply line 36 and a hot air supply line 52.

[0071] In this embodiment, the superheated steam leaving the thermal storage unit 14 passes first through a regenerative heat exchanger 40 and then through a steam cycle steam turbine 38 to generate electricity. The electricity can be diverted to supply the electrolyzer 16 or can be used for other purposes by connecting external equipment to a power take-off 58. The outlet of the steam turbine 38 is recuperated 36 at low pressure and returned to the steam inlet 22. This steam is heated by a regenerative heat exchanger 40 which recovers heat from the superheated steam leaving the thermal storage unit 14 to raise the temperature of the steam 36 entering the electrolyzer 16.

[0072] According to the present invention, energy in the form of heat in the by-products of the electrolysis reaction in the electrolyzer 16 is stored in a heat storage unit. This heat can be used to provide electricity and / or steam to the electrolyzer, either alone or simultaneously. In this way, intermittent power flow or power dips from intermittent or fluctuating electricity sources can be smoothed out by reusing the stored energy.

[0073] The electrolyzer system 10 comprises a main electricity supply from one or more sources. In this example, this may be renewable energy sources such as solar panels 48, wind turbines 46, and hydropower 50. Typically, only one of these may be present. The electrolyzer 16 comprises at least one stack 28 of solid oxide electrolysis cells (SOECs) for carrying out the electrolysis reaction. This reaction converts water (in the form of steam) into hydrogen and oxygen. The effluent gases from the anode and cathode heat a thermal storage unit 14, which stores at least a portion of the excess heat contained in the exhaust gases emitted by the SOEC.

[0074] The thermal storage unit 14 may provide steam to a steam turbine 38 that generates electricity. The steam turbine also provides low pressure steam for return to the electrolyzer 16.

[0075] In one example, a thermal storage unit uses molten salt to store excess heat. The operating temperature of a molten salt storage system is typically between 150°C and 565°C. This range significantly overlaps with the operating temperatures of low- and intermediate-temperature SOECs and is therefore suitable for thermal coupling with an SOEC as described above. In use, the excess heat is used to heat the molten salt, and a steam generator is used to extract heat as needed. As described above, this steam can drive a turbine to generate electricity, to provide steam for an SOEC, or both simultaneously.

[0076] Alternatively, the thermal storage unit can be a metal hydride or metal carbonate-based storage system. These systems can have higher thermal storage densities than molten salts, but are more complex and costly. Metal hydride and metal carbonate energy storage utilize thermochemical reactions to store excess energy, which can be delivered as steam and / or electricity, as described above. These technologies can also be designed to have operating temperatures that overlap with those of SOECs, making them suitable for thermal coupling with SOECs, as described above.

[0077] Other heat storage units operating on similar principles that may be suitable in the present context include latent heat storage units, hot silicon technology units, steam accumulation units, and molten aluminum technology units.

[0078] In many of these cases, it is possible to design thermal storage units with higher power densities than electric batteries. Additionally, storing excess electricity in the form of heat is beneficial, as this excess energy may later be needed in the form of heat to provide steam and / or to maintain the temperature of the SOEC stack.

[0079] The regenerative heat exchanger 40 serves to mitigate heat losses to the steam produced by the thermal storage as it passes through the steam turbine. Thus, it essentially cools the high temperature steam released by the thermal storage unit and then reheats the steam that has passed through the steam turbine 38 so that it is at the correct temperature for introduction into the electrolyzer 16 as its water source. It is important to note that the regenerative heat exchanger 40 shown is not required, but rather a convenient means of ensuring that the steam re-entering the SOEC is at the correct temperature. This could also be achieved by a heater and / or heat exchanger with another (hot) stream in the system.

[0080] 3, the basic structure and operation of the electrolyzer 16 is shown with reference to one electrolysis cell 20 of the stack 28. These electrolysis cells may also be known as regenerative fuel cells.

[0081] The electrolysis cell 20 comprises an anode 60, a cathode 62, and an electrolyte 64, in a configuration known in the art. Water (here in the form of steam) is supplied to the cathode 62, and hot air (optionally useful as an extraction stream) is supplied to the anode 60. Furthermore, a current / voltage is applied to the electrolysis cell 20 via electrical terminals 66, 68. As a result, an electrolysis reaction occurs across the electrolyte, causing oxygen ions to pass through the electrolyte from the cathode to the anode. Thus, a portion of the steam is decomposed into hydrogen on the cathode side of the electrolysis cell 20, and oxygen is produced on the anode side.

[0082] The oxygen can be extracted using a sweep stream, for example, via air flow through the inlet side to exhaust the exhaust gases through the exhaust gas outlet 36 on the anode side.

[0083] The hydrogen can instead be extracted by the remaining steam stream and discharged through another exhaust gas outlet 24 on the cathode side (a small portion of the steam is converted to hydrogen and oxygen). This makes the steam leaving the cathode side "hydrogen-rich" and the air leaving the anode side "oxygen-rich". These exhaust gases are at approximately the same temperature as the operating temperature of the electrolysis cell, which for an SOEC is typically above 400°C.

[0084] This operating characteristic of SOECs is well known in the art and is beneficial to the present invention because it allows the heat in the exhaust gases to be efficiently utilized by the heat storage unit 14 rather than being wasted.

[0085] The exhaust gas from the SOEC passes through the heat source inlet and the residual heat generated from the exhaust gas is stored in the heat storage unit 14 .

[0086] Referring to Figure 2, a second embodiment of the present invention is shown. This figure has many elements in common with those shown in Figure 1, and the same reference numerals are used. For the sake of brevity, a detailed description of the common elements will be omitted.

[0087] As can be seen, this also shows an electrolyzer system 10 comprising an intermittent or variable electricity source 12, such as a wind turbine, solar panels, or hydropower, and a thermal storage unit 14 with two heat source inlets 18 (one for hot oxygen-rich air and one for hot hydrogen-rich steam). It also comprises an electrolyzer 16, which also typically comprises at least one stack 28 of electrolysis cells (not shown). The electrolyzer 16 again has a steam inlet 22 and two exhaust gas outlets 24, 26 for supplying exhaust gases (typically oxygen-rich air and hydrogen-rich steam) to the thermal storage unit 14. In this embodiment, the thermal storage unit 14 is shown to have outlet ports 102, 104 for supplying the exhaust gases (typically oxygen-rich air and hydrogen-rich steam) to another location or to a bulk storage, after heat has been extracted into the thermal storage unit 14. Similar outlet ports may be present in the first embodiment, but are not shown for simplicity. However, instead of the turbine 38 and recuperator 40, a steam cycle 70 is provided that is driven by hot gas or hot fluid exiting the thermal storage unit 14. This steam cycle 70, or the steam turbine 38 of the previous embodiment, can also be integrated into the thermal storage unit 14 if desired.

[0088] In this embodiment, the hot fluid exits the thermal storage unit 14 via an outlet 74 and enters the steam cycle 70 via an inlet 76. A steam generator and steam turbine, or other electrical energy generating device, may be located within the steam cycle 70 to utilize the steam or heat from the thermal storage unit to provide electrical power generation. Steam utilized in the steam cycle 70 may exit the steam cycle 70 via a steam exhaust 78, while the generated electrical energy exits the steam cycle 70 via an outlet 80.

[0089] 2, by providing a bypass 72 in the steam cycle, heat from the thermal storage unit can be transferred directly to the steam supply line 36 for the SOEC. The hot fluid exiting the thermal storage unit 14 is then typically steam. This may eliminate the need for a steam generator in the steam cycle. This allows a separate water supply (e.g., via a heat exchanger or heating loop) to be heated instead to heat or generate steam.

[0090] 2 also shows an optional external steam source 82. The external steam source 82 can originate from an external industrial process (not shown). Alternatively, it could be a water source to be heated by steam (or a heated fluid) passing through the steam supply line 36. Because the steam comes from the steam supply line 36, if the external steam source is intermittent or missing, it can be compensated for with steam from the steam supply line 36.

[0091] Thus, steam is supplied along the steam supply line 36, and optionally from an external steam source 82, towards the electrolyzer 16. It then flows towards the electrolyzer 16 through a heat exchanger 84. In this embodiment, the steam is heated through the heat exchanger 84 (since it has been cooled by the steam cycle). The heat exchanger cools the hydrogen-rich steam that leaves the electrolyzer 16 through the first exhaust gas outlet 24 of the electrolyzer 16. Because it is preferred that the steam entering the electrolyzer 16 is at or near the operating temperature of the electrolyzer 16, an auxiliary heater 90 may be connected across the steam line 94. This first auxiliary heater 90 may be powered by the intermittent or variable electrical source 12 or by electrical energy leaving the steam cycle 70. In this example, its outlet terminal 80 is connected in circuit back to the circuit 96 of the intermittent or variable electrical source.

[0092] This circuit 96 is also shown supplying power to the electrolyzer 16 via electrolyzer power supply line 98. However, this circuit also extends to a second auxiliary heater 88 and a third auxiliary heater 92 to provide optional functionality as described below. Power can also be supplied elsewhere via power take-off 58 if required.

[0093] These circuits are shown only schematically for ease of reference.

[0094] A second auxiliary heater 88 is for heating the hot air supply before it enters the anode side of the electrolytic cells in the electrolytic cell 16 at the hot air inlet 32. This is optional and is only needed if the hot air (which in some embodiments may be hot nitrogen or other suitable sweep gas, depending on whether a suitable source is available from a nearby industrial process or storage source) has not been sufficiently preheated. A control system may control these auxiliary heaters 88, 90, 92.

[0095] The hot air is supplied from a mixture of ambient air and optionally preheated air from the thermal storage unit 14. In the latter case, the thermal storage unit 14 may be provided with an air inlet 44, as in the previous embodiment, which heats the air within the thermal storage unit before sending it along the hot air supply line 52 to the second heat exchanger 86 or the second auxiliary heater 88 (or both). A bypass line 96 is shown to bypass the second heat exchanger 86 if not required. A similar bypass may be provided for the first heat exchanger 84.

[0096] In this embodiment, the second heat exchanger 86 uses the hot oxygen-enriched air exiting the second exhaust gas outlet 26 of the electrolyzer 16 to heat the ambient air before it enters the electrolyzer. A second auxiliary heater 88 supplements that heating if required. However, if the ambient air is mixed with hot air from a thermal storage unit, the second heat exchanger 86 may not be necessary. This could also serve to heat the exhaust gas if the thermal storage unit becomes hotter than the electrolyzer.

[0097] A third auxiliary heater 92 is provided (possibly with an external heat source, e.g., from a nearby industrial process) to heat the thermal storage unit. This could also be powered by an intermittent or variable electrical source, or power from the steam cycle, or both.

[0098] The provision of heat exchangers and auxiliary heaters allows for a wide range of heat, steam, and power sources (intermittent, variable, or constant) to be accommodated, and supply outages, fluctuations, or reductions can be compensated for, as needed, by the heat stored in the thermal storage unit 14 via the power and steam exiting the steam cycle 70.

[0099] The present invention has been described above with reference to the drawings and claims. Those skilled in the art will recognize that various modifications and variations are possible without departing from the scope of the invention, as defined by the appended claims. For example, features described as part of one embodiment can be used in another embodiment to yield a still further embodiment. It is therefore intended that the present invention cover such modifications and variations as come within the scope of the appended claims.

[0100] Reference signs in the claims are used for illustrative purposes only and shall not limit the scope of the claims.

Claims

1. 1. An electrolyzer system comprising: a thermal storage unit; an electrolytic cell; the thermal storage unit includes at least one heat source inlet; the electrolyzer comprises at least one electrolysis cell, a steam inlet, and at least one exhaust gas outlet, the exhaust gas outlet being connected to the heat source inlet for heating the thermal storage unit; the heat storage unit is configured to use its stored heat to generate steam for supplying the steam inlet and steam for generating electrical power, either at a time or both simultaneously.

2. 2. The electrolytic cell system of claim 1, wherein the thermal storage unit comprises a hot air outlet and the electrolytic cell has a hot air inlet, the hot air outlet of the thermal storage unit being connected to the hot air inlet of the electrolytic cell for selectively supplying hot air to the electrolytic cell during use of the electrolytic cell system.

3. 3. The electrolyzer system of claim 1 or 2, wherein the thermal storage unit comprises a steam outlet.

4. 4. The electrolyzer system of claim 1 , further comprising a steam supply line for supplying steam from the heat storage unit or a steam turbine connected to the heat storage unit to the steam inlet of the electrolyzer.

5. 5. The electrolyzer system of claim 4, wherein the steam supply line includes a bypass connected between the thermal storage unit and the steam turbine and between the steam turbine and the steam inlet for selectively bypassing the steam turbine.

6. 6. The electrolyzer system of any one of claims 1 to 5, further comprising a steam turbine for selectively producing an electrical output using heat or steam from the thermal storage unit.

7. 7. The electrolyzer system according to any one of claims 1 to 6, wherein the heat storage unit comprises a water inlet and / or an air inlet.

8. 8. The electrolyzer system of claim 1, wherein the thermal storage unit is configured to evaporate water in the thermal storage unit to generate steam.

9. 9. The electrolyzer system according to any one of claims 1 to 8, wherein the exhaust gas outlet is connected to the heat source inlet of the heat storage unit via a supply pipe.

10. 10. The electrolyzer system of any one of claims 1 to 9, further comprising a steam cycle or a steam turbine.

11. Further comprising a regenerative heat exchanger; the regenerative heat exchanger is arranged to exchange heat between an outlet of the steam cycle or steam turbine and the steam inlet of the electrolyzer; 11. The electrolytic cell system of claim 10.

12. 12. The electrolyzer system of any one of claims 1 to 11, wherein said at least one electrolysis cell is a solid oxide electrolysis cell.

13. 13. An electrolyser system according to any preceding claim, wherein the or each electrolysis cell has an operating stack temperature in excess of 400°C.

14. 14. The electrolyzer system according to any one of claims 1 to 13, wherein the thermal storage unit is a molten salt thermal storage unit.

15. 14. The electrolyzer system according to any one of claims 1 to 13, wherein the heat storage unit is a thermochemical heat storage unit.

16. 10. The electrolyzer system of claim 1, wherein the at least one electrolytic cell is part of a stack of electrolytic cells.

17. A system comprising an intermittent or fluctuating electricity source and an electrolyzer system according to any one of claims 1 to 16.

18. 18. The system of claim 17, wherein the intermittent or fluctuating electrical source is configured to power the electrolyzer and to heat the thermal storage unit via a heating element, either simultaneously or separately.

19. 19. The system of claim 17 or 18, wherein the intermittent or fluctuating electrical source is configured to power the electrolyzer, to heat or generate steam for the stack, and / or to generate hot air for the stack, either both simultaneously or separately.

20. 1. A method of operating an electrolytic cell system, the electrolytic cell system comprising: a thermal storage unit; an electrolytic cell; the thermal storage unit includes at least one heat source inlet; the electrolytic cell comprises at least one electrolytic cell, a steam inlet, and at least one exhaust gas outlet, the exhaust gas outlet being connected to the heat source inlet; The method comprises: heating the heat storage unit using exhaust gas from the exhaust gas outlet; using heat stored in the thermal storage unit to generate steam for supplying to the steam inlet and for generating electrical power, either one at a time or both at the same time; A method comprising:

21. The method of claim 20, wherein the electrolytic cell system is as claimed in any one of claims 1 to 16.

22. 22. The method of claim 20 or 21, comprising supplying additional heat to the thermal storage unit from one or more external industrial processes.

23. 23. A method according to any one of claims 20 to 22, comprising selectively using heat from the thermal storage unit to generate hot air for supply to the electrolyser or external equipment.

24. using the stored heat to compensate for fluctuations in the supply to the electrolyzer, the fluctuations comprising: a) heat when steam or hot air or both are supplied to the electrolytic cell, and b) electricity for at least partially powering said electrolytic cell; The method according to any one of claims 20 to 22, wherein the variation is at least one of:

25. 25. The method of any one of claims 20 to 24, comprising selectively supplying at least a portion of the generated electrical power to the electrolysis cell to at least partially power the electrolysis cell.

26. 26. A method according to any one of claims 21 to 25, comprising selectively controlling a stream of steam exiting a steam outlet of the thermal storage unit to supply to each of the electrolyser and a steam turbine for producing electrical power, either individually or both simultaneously.

27. 27. The method of any one of claims 20 to 26, wherein the exhaust gas outlet supplies exhaust gas from the electrolyzer and a gas supply line supplies the exhaust gas through the heat source inlet of the thermal storage unit to heat the thermal storage unit.

28. 28. A method according to any one of claims 20 to 27, comprising reducing the pressure of steam from an inlet pressure as it is supplied to the steam cycle or turbine to a delivery pressure as it leaves the steam cycle or turbine.

29. 29. The method of any one of claims 20 to 28, wherein the electrolyzer system comprises a steam cycle or a steam turbine and a regenerative heat exchanger, the regenerative heat exchanger exchanging heat between an outlet of the steam cycle or steam turbine and the steam inlet of the electrolyzer.

30. 30. The method of any one of claims 20 to 29, wherein the electrolyzer system is connected to an intermittent or fluctuating electricity source, and the electrical power generated using heat stored in the thermal storage unit is used to compensate for power fluctuations of the intermittent or fluctuating electricity source.

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