Pressurisable system

Abstract

A system and method for the system. The system comprising at least two pressurisable fluid volumes which are not in fluidic communication with one another, at least two pressure regulators configured to regulate pressure in the respective at least two pressurisable fluid volumes, at least two pilot lines, each configured to provide a reference pressure to a respective one of the at least two pressure regulators, and a flow restriction device. The system is configured such that in a depressurisation condition the at least two pilot lines are in fluidic communication with one another and with the flow restriction device. Further, in the depressurisation condition, the pilot lines are configured to gradually depressurise by flow of fluid therein through the flow restriction device, thereby reducing the reference pressures for the at least two pressure regulators.

Description

[0001] PRESSURISABLE SYSTEM

[0002] Field of the Invention

[0003] The present invention relates to a system, and in particular a electrochemical cell system configured to operate at an elevated (above ambient) pressure, such as a pressurisable electrolyser system or a pressurisable fuel cell system. The present invention also relates to a method of depressurising the system. The system may comprise at least one stack of electrochemical cell units - typically electrolyser cell units, which may include cell units of solid oxide or molten carbonate electrolyser cells. The present invention more specifically relates to the integration of solid oxide electrolyser cell (SOEC) units within an enclosure to form the pressurisable electrochemical cell system. The solid oxide electrolyser cell (SOEC) units may include metal-supported solid oxide electrolyser cell (MS-SOEC) units.

[0004] Background to the Invention

[0005] Electrochemical cell units are commonly referred to as fuel cell units or electrolyser cell units, and in some instances their names are interchangeable as some fuel cell units can work as electrolyser cell units and some electrolyser cell units can operate as fuel cell units, each either as a producer of electricity or in a regenerative mode - electrolyzing a fluid to electrochemically split it into two or more component parts. For example, some fuel cell units can produce electricity by using an electrochemical conversion process that oxidises fuel to produce electricity. Some fuel cell units can also, or instead, operate as regenerative fuel cells (or reverse fuel cells) units, often known as electrolyser cell units, for example to separate hydrogen and oxygen from water, carbon monoxide and oxygen from carbon dioxide, or nitrogen monoxide and oxygen from nitrogen dioxide.

[0006] Electrochemical cell units may be tubular or planar in configuration. Planar cell units may be arranged overlying one another in a stack arrangement, for example 100-400 cell units in a stack, with the individual fuel cell units arranged, for example, electrically in series. Tubular cell units may be arranged in groups, stacks or coils thereof.

[0007] A solid oxide fuel cell (SOFC) unit that produces electricity is based upon a solid oxide electrolyte that conducts negative oxygen ions from an oxygen electrode to a fuel electrode located on opposite sides of the electrolyte. For this, a fuel, or reformed fuel, contacts the fuel electrode and an oxidant, such as air or an oxygen rich fluid, contacts the air electrode. A solid oxide electrolyser cell (SOEC) may have the same structure as an SOFC but is essentially that SOFC operating in reverse, or in its regenerative mode, to achieve the electrolysis of fuel, for example water and / or carbon dioxide, by input of electrical energy and using the solid oxide electrolyte to produce hydrogen gas and / or carbon monoxide and oxygen. Conventional ceramic-supported (e.g. fuel electrode-supported) SOFCs and SOECs have low mechanical strength and are vulnerable to fracture. Hence, metal-supported SOFCs and SOECs have been developed which have the active cell component layer supported on a metal substrate. In these cells, the ceramic layers can be very thin since they only perform an electrochemical function: that is to say, the ceramic layers are not self-supporting but rather are thin coatings / films laid down on and supported by the metal substrate. Such metal-supported SOEC stacks are more robust, lower cost, have better thermal properties than ceramic-supported SOECs and can be manufactured using conventional metal welding techniques.

[0008] Electrolyser cell stacks commonly operate at elevated temperatures. For example, intermediate or high temperature electrolysers (such as SOEC and alkaline electrolyte cells) have operational temperatures in excess of 400 °C, typically 450 °C to 700 °C for an intermediate temperature electrolyser such as one based on an MS-SOEC, and above 700 °C for high temperature electrolysers.

[0009] Electrolyser cell stack(s) can be assembled within a housing, and can be combined with heat exchangers and fluid delivery pipework, amongst other equipment, to form an electrolyser system, and the electrolyser system will be configured to supply input gas to and exhaust off-gas from the electrolyser cell stack(s) at the required operational temperatures.

[0010] The electrochemical cell units may themselves be pressurisable and / or they can be integrated within a pressurisable enclosure, for forming a pressurisable system. There can be times when the system needs to be depressurised.

[0011] In some electrochemical cell systems, for example where the electrochemical cell units are solid oxide electrolyser cell (SOEC) units, or more specifically metal-supported solid oxide electrolyser cell (MS-SOEC) units, at least some of the components may have ceramic or relatively brittle components within them. Such components can be relatively fragile, or temperamental when exposed to bending forces or unexpected (or out-of-the-ordinary) mechanical strains or stresses. Rapid depressurization events, for example, can create pressure imbalances across surfaces of the cell units, or force-imbalances either side of the components. These can lead to such bending forces or unexpected (or out-of-the-ordinary) mechanical strains or stresses. These in turn can lead to cracking of the ceramic components, or other failures or defects within the cell units.

[0012] The present invention seeks to reduce a likelihood of such bending forces or unexpected (or out- of-the-ordinary) mechanical strains or stresses, and to thus reduce or eliminate the opportunities for such consequential failures or defects.

[0013] SUMMARY OF THE INVENTION

[0014] According to a first aspect of the present invention there is provided a system comprising: at least two pressurisable fluid volumes which are not in fluidic communication with one another; at least two pressure regulators configured to regulate pressure in the respective at least two pressurisable fluid volumes; at least two pilot lines, each configured to provide a reference pressure to a respective one of the at least two pressure regulators; and a flow restriction device; wherein the system is configured such that in a depressurisation condition: the at least two pilot lines are in fluidic communication with one another and with the flow restriction device; and the pilot lines are configured to gradually depressurise by flow of fluid therein through the flow restriction device, thereby reducing the reference pressures for the at least two pressure regulators.

[0015] In this way, it will be understood that depressurisation of the fluid volumes can be achieved by reduction of the reference pressure provided to the pressure regulators (via the pilot lines), rather than the usual arrangement of providing a separate pressure relief value or path. In other words, in the depressurisation condition, fluid from the fluid volumes can be exhausted through the pressure regulators that are usually used to maintain a specific pressure, albeit those pressure regulators can have their reference pressure rapidly de-rated, by action of exhausting the (common) pilot line through the flow restriction device. The present inventors have found that this arrangement has particular advantage for depressurising multiple different volumes while at all times ensuring that the pressure difference between those volumes is kept to a minimum.

[0016] The system may be configured to be operated at a pressure above ambient pressures, and as such may be referred to as a pressurisable system.

[0017] As the pilot lines are in fluidic communication in the depressurisation condition, they are configured such that in use they will have substantially matched or identical fluidic pressures.

[0018] As the matched or identical fluidic pressures define the reference pressures provided to the pressure regulators, the pressurisable fluid volumes can be configured to depressurise in parallel.

[0019] In some embodiments, the flow restriction device is configured to control the rate at which the pilot lines depressurise such that the pressurisable fluid volumes can depressurise with substantially matched or identical pressures at any point in time during the depressurisation process. In other words, the at least two pilot lines depressurise through the same flow restriction device (which may include at least one flow restriction element on a fluidic path through said device).

[0020] In some embodiments, there are three or more pressurisable fluid volumes, and the system is configured to contain within the pressurisable fluid volumes at least two fluids of differing fluidic properties or compositions, i.e. different fluids in at least two of the pressurisable fluid volumes. In some cases there may be two and in other cases there may be three different fluids in the three or more pressurisable fluid volumes. Differing fluidic properties may include viscosity, density, compressibility, temperature and so forth, and these may affect how a fluid flows, e.g., how it flows through a restriction or regulator. It will be understood that each pressurisable fluid volume may be configured to contain more than species. For example, a first pressurisable fluid volume may be configured to contain a mixed fluid (in the case of an electrochemical system, this may be air or an inert gas (e.g., nitrogen and oxygen) and a second pressurisable fluid volume may be configured to contain a second mixed fluid (in the case of an electrochemical system, this may be hydrogen and water, where steam or hydrogen are the fuel).

[0021] Each pressurisable fluid volume typically is not in fluidic communication with the others.

[0022] Each pressurisable fluid volume may be provided with its own pressure regulator, its own pilot line and reference pressure, and all pilot lines, in the depressurisation condition, are configured to be in fluidic communication with one another and with the flow restriction device

[0023] In some embodiments, the at least two pilot lines are configured to contain fluids of similar fluidic properties. For example, they may contain the same fluidic species.

[0024] In some embodiments, each pilot line is configured to contain fluid substantially comprising or consisting of an inert gas. For example, the fluid may be nitrogen - or a gas that is greater than or equal to 95% by weight nitrogen. In some embodiments, the fluid in the pilot lines is air.

[0025] In some embodiments, the system is configured such that the pilot lines are configured to be fluidically isolated from one another in operational conditions, i.e. non-decompression conditions. They may be configured to be individually pressure controlled by a respective electronic pressure controller, and they may be configured to be provided pressurised fluid by a supply line. Operational conditions, i.e. non-decompression conditions, may include normal operational conditions, start-up / warm up conditions, standby conditions, steady-state conditions and in the case of an electrolyser system, product-generating conditions.

[0026] In some embodiments, the system can be configured such that the pilot lines are configured to be fluidically isolated from one another even in certain specific decompression conditions, such as normal or planned shut-down modes, during which the decompression of the pressurisable fluid volumes are controlled by the at least one electronic pressure controller(s) connected to the pilot lines. The decompression condition in which the pilot lines are in fluidic connection can then be an unplanned or emergency decompression condition.

[0027] Each pilot line may comprise at least one normally closed valve. At least one normally closed valve may be provided between the supply and the electronic pressure controller.

[0028] At least one normally open valve may also be provided for the system - for example shared by the pilot lines. Usually, however, each pilot line may comprise at least one normally open valve to provide redundancy. At least one normally open valve may be provided on each pilot line between the respective pressure regulator and the flow restriction device (for example, before and after a joining point for the pilot lines).

[0029] The pressure regulators may be back pressure regulators.

[0030] In some embodiments, the system can be configured such that in the decompression condition, the pilot lines are fluidically connected by opening at least one normally open valve, such as one or both of the normally open valves, and said normally open valve(s) is / are configured to be controlled to be closed in the operational (i.e. non-decompression) conditions (and where provided for, the certain specific decompression conditions). In some embodiments, each pilot line comprises a respective pressure controller which, in operational conditions, is configured to set the reference pressure in the respective pilot line for the pressure regulator of the allocated pressurised fluid volume and is configured during operational conditions to be in fluidic communication with its supply line that is configured to supply fluid to the pressure controller. The supplied fluid may then pass therethrough to the pilot line, and thereon to the connected pressure regulator.

[0031] In operational conditions, the pressure controllers thus are each configured to control, via its pilot line and the pressure regulator of an assigned fluid volume, the pressure in the respective one of the at least two pressurisable fluid volumes. In some embodiments, in operational conditions, the pressures within the pilot lines are controlled by the pressure controllers to be at substantially equal pressures. This can be by using a control system connected to the respective pressure controllers. In some embodiments, the control system or the pressure controllers, or both, are configured to maintain a difference in pressure between the separate fluid volumes at no more than 0.5 bar, optionally no more than 0.2 bar, optionally no more than 0.1 bar, optionally no more than 0.05 bar, or optionally no more than 0.01 bar.

[0032] In some embodiments, the fluid in the first fluid volume contains oxygen at a percentage by weight exceeding 18%. In some embodiments, the second fluid volume contains a fuel gas - for example a hydrocarbon or hydrogen based fuel for a fuel cell or a fluid for electrolysis (such as steam or carbon dioxide) for an electrolyser cell. In some embodiments the third fluid volume contains air or a gas containing at least 70% nitrogen. In some embodiments the third fluid volume is a housing or case surrounding the fuel cell or the electrolyser cell, or at least one stack of such cells.

[0033] In some embodiments, although the intention is for substantially equal pressures, there will inevitably be small pressure differences between the fluid volumes, so the systems are controlled to maintain specific direction of pressure differences. For example, the oxygen side of the cells within a stack may be maintained at a slightly higher pressure than a fuel side of the cells within a stack.

[0034] In some embodiments, at least one of the pilot lines, and usually each pilot line, comprises at least one tank configured to retain a volume of supplied gas - the volume being at least two times larger than the volume of the rest of the pilot line. The pressure within the tank is generally maintained at the same pressure as the rest of the pilot line by the tank and the rest of the pilot line being in fluid communication. By adding a tank to the pilot line, a larger volume of fluid is present in the pilot line, thus increasing the time for it to depressurise by a flow of fluid through the flow restriction device (the flow restriction device being located downstream of the tank and the pressure controller). As the tank provides an extra volume of fluid for the pilot line, this enables a more gradual depressurisation, minimising chances of an unintended pressure differential between the separate fluid volumes. In some embodiments, where there is more than one pilot line only one of the pilot lines may be provided with a tank and / or there may be fewer tanks than pilot lines. This reduces complexity and cost of the system while maintaining the benefit of a tank, as the pilot lines are fluidically connected in a depressurisation condition. In some embodiments, the volume of each tank is at least 0.5 litres, up to a maximum of 10 litres. More preferably its volume is between 1 and 5 litres.

[0035] In some embodiments, instead of, or in addition to a small tank, the pilot lines may be provided with at least a portion of its length being a bigger diameter, or long extended or coiled length of pipe, for increasing the fluidic volume of the pilot line versus a traditional diameter of pipe therefor.

[0036] In some embodiments, a depressurisation condition of the present invention can be a planned shutdown, or an operator triggered or emergency shutdown. This might occur, for example, if a problem is noted, or if there is an interruption of power to the system, or in the event of a pressure controller or pressure regulator failure, or due to a detected leak or contamination within the system, or some other safety-related failure or detected condition.

[0037] In some embodiments, the flow restriction device is passive or unpowered, so that any pressure difference between the pressurisable fluid volumes is able to be substantially equalised during a depressurisation condition, irrespective of the reason for depressurisation, for example even in the event of a power failure. For example, in some embodiments the flow restriction device comprises an orifice, an orifice plate, an orifice aperture, a flow contraction, a screen, a perforated plate, or a through flow valve configured to provide a flow-rate restriction in the depressurisation condition.

[0038] The pilot lines may be separated from the flow restriction device in normal operating conditions - for example by at least one normally open valve (e.g. that is powered to be closed in normal operating conditions). In some embodiments, the exit of the flow restriction device is instead (or also) separated from an exhaust of the pilot line(s) in normal operating conditions, for example by at least one normally open valve, e.g. that is powered to be closed in normal operating conditions.

[0039] In some embodiments, the at least two pressurisable fluid volumes comprise first and second volumes of electrochemical cell units in an electrochemical cell system. In some embodiments, the system is an electrolyser system.

[0040] In some embodiments, the at least two pressurisable fluid volumes comprise first and second volumes of electrolyser cell units in the electrolyser system - for example the cathode and anode sides of the cell units, or the fuel and oxygen sides of a stack thereof. In some embodiments, the at least two pressurisable fluid volumes comprise (or consist of) first and second volumes of electrochemical cell units in the electrochemical system - for example the fuel and oxygen sides of a stack thereof. In some embodiments, the at least two pressurisable fluid volumes comprise first and second volumes of fuel cell units in a fuel cell system - for example the fuel and oxygen sides of a stack thereof.

[0041] In some embodiments the third pressurisable fluid volume is a common volume within a pressure vessel within which the cell units are positioned.

[0042] In some embodiments, there are two pressurisable fluid volumes, one of the fluid volumes being a common volume within a pressure vessel within which the cell units are positioned, said common volume being in fluidic communication with one of a fuel side or an oxygen side of the cell units, and the other of the pressurisable fluid volumes being the other of the fuel side and the oxygen side of the cell units. In such an embodiment, the pressure of the common volume is not independently controlled relative to the fuel side and the oxygen side of the cell units, but is instead at the same pressure as the said one of the fuel side and the oxygen side of the cell units due to the fluidic connection therewith.

[0043] In some embodiments, the pressure within the fluid volumes is maintained in normal operational conditions to be at least 0.5 barg, optionally at least 1 barg, optionally at least 1.5 barg, optionally between 1.5 barg and 3 barg, optionally no more than 10 barg, or optionally no more than 5 barg. 1 barg is 1 bar above ambient, i.e. typically around 2 bar.

[0044] In some embodiments the pressure regulators are back pressure regulators.

[0045] In some embodiments exhausts of the system (i.e., of the pressurisable fluid volumes and the pilot lines) link together downstream of the flow restriction device (which, for the pressurisable fluid volumes may also be subsequent to other components, for example heat exchangers for transfer of heat from fluid exhausted from said volumes to other fluid).

[0046] In some embodiments, a controller is provided for the system, the controller being configured to, in operational conditions, control all normally open valves of the pilot lines to be in a closed state, and all normally closed valves of the pilot lines to be in an open state.

[0047] In some embodiments, the controller is configured to, in a depressurisation condition, control or release all normally open valves of the pilot lines to revert to an open state, and all normally closed valves of the pilot lines to a closed state. In some cases the normally open valves revert to an open state and the normally closed valves revert to a closed state by default (e.g., due to the absence of a command from the controller to be in the opposite, powered, state)

[0048] The present invention also provides a system comprising: at least one pressurisable fluid volume; at least one pressure regulator configured to regulate pressure in the pressurisable fluid volume; at least one pilot line, configured to provide a reference pressure to the pressure regulator; and a flow restriction device; wherein the system is configured such that in a depressurisation condition: the pilot line is configured to gradually depressurise by flow of fluid therein through the flow restriction device, thereby reducing the reference pressure for the pressure regulator.

[0049] The system may also comprise any one or more of the features defined above for the preceding embodiments, or as defined below.

[0050] In some embodiments, the system of either aspect may comprise a pressure controller in the pilot line configured to set the reference pressure in the pilot line and in fluidic communication with a supply line configured to supply fluid to the pilot line. For example, the pressure controller may be an electronic pressure controller.

[0051] In some embodiments, the system of either aspect may comprise an exhaust configured to be downstream of the flow restriction device. In some embodiments the exhaust may be in a branch of the pilot line, for example controlled by a separate valve - for example a normally open valve.

[0052] In some embodiments, the flow restriction device is in a (or the) branch of the pilot line, for example controlled by a (or the) separate valve - for example a (or the) normally open valve.

[0053] In some embodiments, during non-depressurisation conditions, i.e. normal operational conditions, the pressure controller is configured to be in fluidic communication with the supply line, the flow restriction device is configured to be fluidical ly isolated from the first pilot line, and the reference pressure is a pressure value and is configured to regulate (via the pressure regulator) the pressure in the first fluid volume at the pressure value.

[0054] In some embodiments, in the depressurisation condition, the (electronic) pressure controller is configured to be fluidically isolated from the supply line, for example by a valve - such as a normally closed valve, the flow restriction device is configured to be in fluidic communication with the pilot line, and the flow restriction device is configured to allow fluid in the pilot line to pass through the flow restriction device to a or the exhaust, thereby being configured to depressurise the pilot line and decrease the reference pressure provided to the pressure regulator, and in turn decrease the pressure in the fluid volume.

[0055] The present invention also provides a system comprising: at least one pressurisable fluid volume comprising at least a first fluid volume, a pressure regulation subsystem configured to regulate pressure in the first fluid volume, and a flow restriction device, the pressure regulation subsystem comprising: a pressure regulator configured to regulate the pressure in the first fluid volume, a pilot line configured to provide a reference pressure to the pressure regulator, a pressure controller in the pilot line configured to set the reference pressure in the pilot line and to be in fluidic communication with a supply line configured to supply fluid to the pilot line, an exhaust configured to be downstream of the restriction device, wherein: the flow restriction device is in a branch of the pilot line; during operational conditions: the pressure controller is configured to be in fluidic communication with the supply line, the flow restriction device is configured to be fluidically isolated from the first pilot line, and the reference pressure is a pressure value and is configured to regulate the pressure in the first fluid volume at the pressure value, and in a depressurisation condition: the pressure controller is configured to be fluidically isolated from the supply line, the flow restriction device is configured to be in (optionally selective) fluidic communication with the pilot line, and the flow restriction device is configured to allow fluid in the pilot line to pass through the flow restriction device to the exhaust, thereby being configured to depressurise the pilot line and decrease the reference pressure provided to the pressure regulator, and in turn decrease the pressure in the fluid volume.

[0056] This system may also be in accordance with any of the preceding or following aspects or embodiments.

[0057] In some embodiments, the pressure regulation subsystem further comprises at least one tank configured to be at the same pressure as the pilot line and configured to be depressurised by flow of fluid from the tank via the flow restriction device.

[0058] In some embodiments, the system comprises at least a first pressurisable volume and a second pressurisable volume which are fluidically isolated from one another.

[0059] In some embodiments the first and second pressurisable volumes, each comprise a respective pressure regulation subsystem configured to regulate pressure in the respective pressurisable volume to respective pressure values, the respective subsystems having the same pilot line composition as defined above. For example, the system may further comprise respective first and second pressure regulation subsystems configured to regulate pressure in respective first and second pressurisable volumes to first and second values, the respective subsystems each having fluid in a pilot line, but both being in (optionally selective) fluidic communication with the same flow restriction device.

[0060] In some embodiments, the system further comprises a third pressurisable volume, the third pressurisable volume also comprising a pressure regulation subsystem as defined above.

[0061] In some embodiments, the valves are solenoid valves. Solenoid valves are controllable and suited to operation in the described systems.

[0062] The present invention also provides a method of controlling a system as defined above, comprising a controller for carrying out a process of decompressing the fluid volume(s) in a depressurisation condition using the restriction device to control depressurisation of the pilot line(s).

[0063] Preferably, the system comprises at least two pressurisable volumes within a fuel cell unit or an electrolyser cell unit, the volumes being separated in the cell units by an electrolyte layer of the cell units, and the controller regulates the depressurisation to regulate the pressures either side of the electrolyte layer to balance the pressures either side of the electrolyte layer. These pressurisable volumes may be a fuel volume and an oxygen volume (or a cathode volume and an anode volume). There may also be a pressure vessel volume (e.g. a common volume containing the cell units) as a third pressurisable volume (or as part of one of the first and second volumes - if fluidically connected thereto). The pressure may be balanced such that a difference in pressure between the volumes is no more than 0.5 bar, optionally no more than 0.2 bar, optionally no more than 0.1 bar, optionally no more than 0.05 bar, and optionally no more than 0.01 bar. Balancing the pressure comprises controlling any pressure imbalance to reduce or substantially eliminate a pressure difference across the cell units.

[0064] According to an aspect of the invention there is provided a controller configured to perform the methods discussed herein.

[0065] According to an aspect of the invention there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to the aspects above. In particular, when the program is executed by a computer, this causes the computer to carry out the method.

[0066] According to an aspect of the invention there is provided a non-transitory computer-readable medium with instructions stored thereon, that when executed by a processor, perform or cause the processor to perform the method. In particular, when executed by a processor, perform or cause the processor to perform the method.

[0067] In some embodiments, the cell units are contained in stacks and the volumes are within the anode and cathode sides of the stacks. In some embodiments there are multiple stacks and stacks are arranged in arrays of stacks, for example in a pressure vessel. Connections may extend between the stacks and to manifolds for passing fluid to and from the stacks. Each manifold may comprise at least one channel or pipe.

[0068] In some embodiments, the manifolds and connections define an inlet manifold configured to provide fluid to each of said stacks and / or a product manifold configured to exhaust off-gas or product from each of said stacks. An inlet manifold for fuel may be defined. The fluid may be a fuel, which may be a combustible fluid if the electrochemical cell system is operating in a power delivery mode, or a fluid for separation (e.g. at least one of water / steam, carbon dioxide and nitrogen dioxide) if operating instead in a regenerative mode. A second inlet manifold for sweep gas or oxidant (provided to an oxygen volume) may be provided. At least one product manifold, for off-gas from a fuel or oxygen volume of the stacks may be provided, in some embodiments separate product manifolds are provided for off-gas from the fuel and oxygen volumes respectively.

[0069] The pressurisable volumes may contain the oxygen (e.g., anode for electrolysis) and fuel (e.g., cathode for electrolysis) sides of the stacks, and usually will additionally include at least one of the manifolds and connections that are fluidically connected to the respective oxygen and fuel sides of the stacks.

[0070] In some embodiments the stacks are configured as at least one array of stacks. Each array may have its own manifolds and connections, although a manifold and connections therefrom may instead connect with multiple arrays. In some embodiments a manifold is fluidically connected with multiple arrays (preferably all arrays) via respective connections (i.e., one connection between each manifold and array). Such fluidic connections may be of a flexible type. In some embodiments each array is at least one pair of stacks, arranged side by side, and multiple pairs may be spaced along the length of the enclosure, e.g. in rows. For example, each row may have at least one pair of stacks, and there may be multiple rows.

[0071] In some embodiments, said pressure vessel defines an enclosure that includes a plurality of interfaces or control circuits to provide or control fluid and electrical connections to said manifolds and electrical conductors. In some embodiments, all of said interfaces or control circuits are located on a removable lid for, or on an outside of, the enclosure.

[0072] The cell units may be electrochemical cell units such as fuel cell units or electrolyser cell units.

[0073] In some embodiments, the cell units may be based on a solid oxide electrolyte and so are solid oxide electrochemical cells (SOEC).

[0074] The electrolyser cell units may be metal-supported electrolyser cells (e.g., MS-SOEC), which aids stability of said cell units.

[0075] In some embodiments the electrochemical cell units operate at a target operational temperature in excess of 400 °C (e.g., 400-800 °C, or 450-700 °C). The temperatures referred to may be a temperature of the stack(s) - for example, the temperature of the product or off-gas (from the fuel or oxygen volumes of the stack(s)) may be used as the temperature of the stack(s) or the temperature of the stack(s) derived therefrom.

[0076] Within the or each enclosure, the stacks of that enclosure are generally preferred to be configured to be located within a common volume or space within the enclosure. They may be connected by the or each support bed and the or each manifold to a common electrochemical cell assembly that is connected to the enclosure using bolts, or the common volume or space may contain more than one electrochemical cell assembly.

[0077] The or each enclosure is preferably a sealed vessel once closed by the or each removable lid, and it is preferably a pressure vessel. References to enclosure, vessel and pressure vessel herein may each be used interchangeably.

[0078] To achieve the desired operation temperatures, it may be necessary to heat the stacks. This process may also comprise heating the enclosure or vessel. It may be assumed that the temperature within the volume or space within the enclosure or vessel is substantially the same as that of the stacks and the temperature of either may be measured.

[0079] References to heating the stacks may be replaced with references to heating the enclosure or vessel and vice versa.

[0080] References to supply of a fluid or gas to the stacks may involve providing said fluid or gas to one or both of a fuel volume and an oxygen volume of the cell units within the stacks (i.e. to anode and / or cathode sides of the cell units), unless otherwise specified.

[0081] In some embodiments, for each electrochemical cell assembly, the plurality of stacks are arranged in the enclosure in sets of at least 6 stacks, optionally at least 10 stacks, and optionally at least 20 stacks. For example, if supplied in pairs that are arranged side by side, the stacks may be arranged in an array of stacks that is two wide and in 3, 5 or 10 rows. In some embodiments they may instead be four wide. For example an array may feature a four wide, six row, set of stacks, and thus totalling 24 stacks. Instead there may be 2, 3, 4, 5 or 7 (or more) rows.

[0082] In some embodiments, the common volume is in fluidic communication with one or more of a fuel volume and an oxygen volume of each of the one or more stacks during operational use of the system. For example, the common volume may be fluidically connected with one of fuel and oxygen volumes at an outlet of each stack, and optionally also at an inlet of each stack.

[0083] In some embodiments, the common volume is in fluidic communication with the oxygen volume of each of the stacks. In other words, the oxygen volume of the plurality of stacks is open manifolded (i.e., not manifolded to separate it from the common volume), and thus the oxygen outlet of each stack exhausts fluid from the oxygen volume into the common volume.

[0084] In some embodiments, the fuel and oxygen volumes of each stack are fully manifolded and so neither volume is in fluidic communication with the common volume. In such cases, a vessel fluid is supplied to the common volume within the enclosure. The vessel fluid may comprise a purge gas. The vessel fluid may comprise or consist of nitrogen or air.

[0085] The enclosure may be provided with a common volume inlet and a common volume exhaust for supply to and exhaust from the common volume. The vessel fluid may supply heat to the common volume and the stacks during a start-up cycle for the system.

[0086] In some embodiments, the fuel volume of each of the stacks is manifolded. Preferably, the manifolding is configured such that fuel flows through the plurality of stacks in parallel. The stacks themselves are also typically configured such that the fuel flows through the plurality of cell units in parallel.

[0087] Preferably, the enclosure is a pressure vessel configured to withstand a pressure difference between the inside of the pressure vessel and an ambient pressure surrounding the enclosure.

[0088] In some embodiments, a control system is provided that is configured to regulate (e.g. using back pressure regulation) the pressure of at least one or both of the fuel volume and the oxygen volume of the stacks, and optionally also to regulate pressure in the common volume, for example independently or via fluidic communication between the common volume and one of the fuel and oxygen volumes, at a pressure greater than ambient pressure.

[0089] In some embodiments, the pressure of at least one or both of the fuel volume and the oxygen volume (and optionally the common volume) is at least 0.5 barg, optionally at least lbarg, optionally at least 1.5 barg, optionally between 1.5 barg and 3 barg, optionally no more than 10 barg, optionally no more than 5 barg. 1 barg is 1 bar above ambient, i.e. typically around 2 bar. When pressurised to a pressure higher than ambient pressure, this elevated pressure can be used to balance fluid pressure within the fuel and oxygen volumes of the stacks, thus reducing the stresses within the internal walls of the cell units / stacks. This is beneficial in particular since electrochemically active materials within the cell units of the stacks can be relatively brittle compared to the metal / steel support layer in the case of a MS-SOEC, and the balanced pressures between the stack and the common volume can additionally de-stress the exterior walls of the stacks. In some embodiments, the regulating of the pressures comprises regulating the pressure of the fuel volume and the oxygen volume to balance pressure between the fuel volume and the oxygen volume, and optionally also the common volume, either directly because the common volume is not in fluid communication with the fuel or oxygen volume or indirectly via fluidic communication between the common volume and one of the fuel and oxygen volume. The pressure may be balanced such that a difference in pressure between neighbouring volumes is no more than 0.5 bar, optionally no more than 0.2 bar, optionally no more than 0.1 bar, or optionally no more than 0.05 bar. Balancing the pressure comprises controlling any pressure imbalance, i.e. to reduce or eliminate a pressure difference, across the cell units or stacks by supplying fluid to the fuel or oxygen volumes - or regulating the exhaust from said volumes.

[0090] In some embodiments, the electrolyser system comprises a controller configured to perform the balancing process.

[0091] Particular and preferred aspects of the invention are set out in the accompanying independent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as desired and appropriate and not merely as explicitly set out in the claims. The term "comprising" as used herein to specify the inclusion of components also includes examples in which no further components are present.

[0092] An enabling disclosure of the present invention, to one of ordinary skill in the art, is provided herein. Reference now will be made in detail to examples of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, and not limitation of the invention.

[0093] Brief Description of the Drawings

[0094] Features of the present invention will now be described in further detail, by way of various embodiments, and just by way of example, with reference to the accompanying drawings (which drawings are not to scale), in which:

[0095] Figs. 1 and 2 are simplified schematic views of an electrolyser system;

[0096] Fig. 3 is a simplified control device for controlling an electrolyser system;

[0097] Fig. 4 schematically shows an electrochemical cell unit, which may be a fuel cell unit or an electrolyser cell unit;

[0098] Fig. 5 schematically shows a prior art system for pressurising and depressurising a fluid volume (pressurisable volume);

[0099] Fig. 6 schematically shows a first system in accordance with the present invention for pressurising and depressurising a fluid volume (pressurisable volume);

[0100] Fig. 7 schematically shows a modified version of the system of Figure 6 for pressurising and depressurising a fluid volume (pressurisable volume); Fig. 8 schematically shows a further embodiment, instead for pressurising and depressurising two separate fluid volumes (pressurisable volumes);

[0101] Fig. 9 schematically shows a modified version of the system of Figure 8, adapted for pressurising and depressurising three separate fluid volumes (pressurisable volumes); and

[0102] Fig. 10 schematically shows a modified version of the system of Figure 7 for pressurising and depressurising a fluid volume (pressurisable volume).

[0103] Detailed Description

[0104] In the following figures and description, like reference numerals will be used for like elements in different figures.

[0105] In the following description, the electrochemical cell systems will be described as if they are electrolyser systems (which could be a reversible fuel cell operating in a regenerative mode), for ease of reference. However, it is to be appreciated that the electrochemical cell systems could also be configured as a fuel cell system operating in a power delivery mode.

[0106] Fig. 1 is a simplified schematic of an electrolyser system 100 including a plurality of electrolyser stacks 10 in an enclosure 105. The enclosure 105 may be a pressure vessel 105 configured to withstand a pressure difference between its interior and exterior.

[0107] An array 110 of four stacks 10 is shown in Fig. 1, but it will be understood that any number of stacks 10 may be present, including fewer and greater than four, for example 1, 2, 10, 12 and so forth.

[0108] Each stack 10 comprises a stack of electrolyser cell units. A typical stack may have 100 to 500 electrolyser cell units. An example cell unit 82 is shown schematically in Figure 4.

[0109] The electrolyser cell units 82 each comprise a first fluid volume 60 (for a first fluid 70 - typically fuel for the electrolysis process - e.g. at least one of steam, carbon dioxide and nitrogen dioxide - see Figure 5) and a second fluid volume 62 (for a second fluid 72 - typically oxygen as a product of the electrolysis process), which fluid volumes 60, 62 are fluidically separated from one another such that the first and second fluids therein cannot mix.

[0110] Each stack 10 or cell unit 82 has a first fluid inlet 115 and a first fluid outlet 116, each of which is in fluidic communication with the first fluid volumes of each electrolyser cell unit 10. Supply of the first fluid to the first fluid volume is via the first fluid inlet 115 and exhaust from the first fluid volume is by the first fluid outlet 116. The first fluid is provided to the first fluid volume of the stacks 10 from a first fluid source 143 via the respective first fluid inlets 115 of the stacks 10.

[0111] In the example of Fig. 1, the first fluid is fully manifolded within the system. That is, there is a manifold enclosing the fluid within the system and providing fluidic communication between the first fluid source 143, external to the enclosure 105, and the first fluid inlets 115 of the stacks 10. Likewise, there is a manifold providing fluidic communication between the first fluid outlets 116 of the stacks 10 and a first fluid volume off-gas collection 163, external to the enclosure 105.

[0112] Each stack 10 or cell unit 82 may have a second fluid inlet 122 and a second fluid outlet 123, which, where present, is in fluidic communication with the second fluid volume of each cell unit 10. Exhaust from the second fluid volume is by the second fluid outlet 123, and an optional supply of a second fluid to the second fluid volume is via the optional second fluid inlet 122. The optional second fluid is provided, in this example, as a sweep flow gas to the second fluid volume of the stacks 10 from a second fluid source 144 via respective second fluid inlets 122 to assist in sweeping product (e.g. oxygen) from the cell units.

[0113] In the example of Fig. 1, the second fluid is open manifolded within the system. That is, there is a vessel inlet 120 to the enclosure 105 for delivery of the second fluid to the interior of the enclosure 105 from the second fluid source 144, but there is no branched manifold to deliver the second fluid to respective second fluid inlets 122 of each stack 110. The interior of the enclosure may be referred to as a vessel volume or common volume 24.

[0114] Exhaust from the second fluid volume of the stacks 110 is also open manifolded. That is, there is a vessel exhaust 121 from the enclosure 105 for exhaust of second fluid volume off-gas from the interior of the enclosure 105 to the second fluid off-gas collection 164 - in this example the offgas or product, mixed with the second fluid, but there is no branched manifold between the respective second fluid outlets 123 of each stack 110 and the vessel exhaust 121.

[0115] In some cases the second fluid may be partially manifolded within the enclosure - i.e. there may exist a manifold between the vessel inlet 120 and the respective second fluid inlets 122 of the stacks 110, or there may exist a manifold between the respective second fluid outlets 123 of the stacks 110 and the vessel exhaust 121.

[0116] In some cases both the inlet and exhaust of the second fluid may be manifolded, as depicted in Fig. 2, to ensure that any second fluid (herein in this example a sweep gas) that is supplied to the second fluid volume is effective at sweeping through the cell units, such that the product / off-gas released into the second fluid volume can then be removed therefrom. This will occur particularly during start up, shut down and standby modes.

[0117] In Fig. 2 the electrolyser system 101, which is otherwise similar to the electrolyser system 100 of Fig. 1, includes inlet and exhaust manifolds for the second fluid which communicate with the second fluid source 144 and second fluid collection 164, respectively. Further, electrolyser system 101 has a vessel inlet 120 and a vessel exhaust 121 for a vessel fluid supplied to a common volume 24 of the enclosure 105, that contains the stacks 10, from a common volume supply 165.

[0118] Optionally the vessel fluid can be supplied via a heater 152. Heaters may optionally also be provided for the first and second fluids supplied from the first and second fluid sources 143, 144.

[0119] The vessel fluid may thereafter be exhausted from the common volume to a common volume collection 166 through the vessel exhaust 121. As such, in this embodiment the common volume 24 of the enclosure 105 is in fluid communication with neither the first nor the second fluid volumes.

[0120] When the stacks 10 are operated at elevated pressures, the vessel fluid in the common volume 24 may be regulated to balance the pressure in the common volume 24 with the pressure in the first and / or second fluid volumes 60, 62. Similarly, the pressures may be balanced between the first and second fluid volumes 60, 62.

[0121] The vessel fluid may be a relatively inert gas to avoid corrosion of the components within the enclosure, and to minimized the possibility of a reaction between the vessel fluid and any leakage of product (e.g. hydrogen, carbon monoxide, nitrogen or oxygen) or first and second fluids from the manifolded passages elsewhere within the enclosure. For example, the vessel fluid may be air or nitrogen.

[0122] It will be appreciated that it is sometimes preferable for the second fluid to be open manifolded, as in Fig. 1, or partially manifolded as discussed above, such that there exists fluidic communication between the second fluid volume of the stacks and the interior of the enclosure 105 for pressure equalisation therebetween - in turn simplifying control strategies and pipework required for the respective fluids.

[0123] It will be understood that similar partial or fully manifolded arrangements to those shown schematically in Figs. 1 and 2 are known in the art, albeit not with the stacks being provided in an enclosure.

[0124] In the examples of Figs. 1 and 2, the first fluid volume 60 is typically a fuel volume and, during steady operation, is for fuel - usually steam and / or carbon dioxide, but possibly other compounds for electrolysing, such as nitrogen dioxide. In cases where the electrolyser cell units in the stacks 10 comprise an oxygen ion conducting electrolyte (e.g., solid oxide electrolyte cell units), the first fluid volume off-gas 74 exhausted to the first fluid off-gas collection 163 comprises hydrogen and / or carbon monoxide and / or nitrogen monoxide (dependent on the fuel used). This off-gas is generated in the electrolysis reaction, and is mixed with unspent fuel in the off-gas. The second fluid volume off-gas 76 exhausted to the second fluid off-gas collection 164 instead comprises oxygen that is generated in the electrolysis reaction. The second fluid off-gas 76 may be pure oxygen or oxygen enriched sweep gas if mixed with a sweep gas.

[0125] The second fluid volume off-gas 76 is preferably controlled through selective use of a sweep gas 72 such that it may comprise at least 50% by weight of oxygen generated by the cell units. In some embodiments, the second fluid volume off-gas 76 may be substantially pure oxygen, if purely the product of the electrolysis process, although it might more normally be oxygen enriched air or nitrogen if a sweep gas (air or nitrogen) is also being used. Ideally, however, the oxygen is at least 90% (by weight) pure oxygen when the system 20 is operating at a steady state operation, as the present invention is ideally operated without an externally sourced sweep gas. In such a configuration the stacks are just supplied the first fluid, i.e. one fluid to the first fluid input 115 for each stack 10. Other than the fluid inlet(s) and outlets 115, 116, 122, 123, the stack / electrolyser / vessel will have inputs (terminals 78, 80) for power (for applying a current across the electrolyser cell units 82 in the stacks 10).

[0126] Operationally, a stack 10 will usually want to avoid large pressure differentials across the cell units, so a threshold pressure differential between the first and second fluid volumes 66, 68 can be set appropriately, or the first fluid volume's pressure (on a first side of each cell unit) can be controlled to balance the pressures across the cell units. In one example, the pressure differential can be controlled (and is kept as small as possible) by use of a common regulator system across or between the two sides 60, 62 of the cell units 82 (the anode side and the cathode side, with an electrolyte 64 between anode and cathode). However, in operation it is sometimes advantageous to control the pressure differential to be positive on the second fluid volume's side to ensure that any leaking oxygen leaks into the fuel side, rather than the other way around, which could instead be hydrogen leaking to the oxygen side. This is better for the stack's operational lifetime as there will be less degradation of the electrochemically active layers of the cell units, and less opportunity for an abrupt failure of the cell unit due to combustion of the hydrogen with the oxygen.

[0127] The electrolyser system 100 typically operates at an elevated temperature, for example 400-700 °C for cell units based on a solid oxide electrolyte. It will be appreciated that heat in the first fluid off-gas and the second fluid off-gas will typically be exchanged with (transferred to) the first fluid and, if present, second fluid prior to their delivery to the stacks 10, typically prior to their entry into the enclosure 205 using at least one heat exchanger (but typically two or more heat exchangers such that heat is recovered from the first fluid volume off-gas and the second fluid volume off-gas). In steady state operation said heat exchange may be sufficient to maintain an operating temperature of the electrolyser system 100 when practiced alongside electrical temperature control by varying a power level applied to the electrolyser cell units. Heaters 150 and / or 151 (e.g., an electric heater and / or a trim heater) may be provided in an input stream of the first and / or second fluid, respectively, to provide additional heat to said fluids and for providing additional heat control flexibility within the system. Said heaters may be sized for steady state requirements only, or may also be used for other operational conditions, e.g. warmup or standby.

[0128] In steady state operation, the first and second fluid volume off-gases will usually be at a similar temperature to the operational temperature of the electrolyser cell units. However, a specific delta from the input temperature will depend upon the amount of electrical power supplied to the electrolyser system / stacks / cell units, and the internal resistance of the cell units.

[0129] The electrical power is generally supplied to the stacks with a constant current. The stack is thus operated in galvanostatic conditions. The electrical resistance of the stack thus controls the voltage applied across the stack, and there is thus a variable power draw from each stack and cell unit as the resistance changes. Alternatively the power supplied to the stacks is controlled potentiostatically. Operational efficiency can be best improved by reducing the amount of external heat supplied to the system via its fluid temperature control system - i.e. via the heaters. Where that external heat is provided for free - for example as a waste product of another industrial process, then that external heat can be usefully used without cost - i.e. it provides added financial efficiencies. However, if that external heat has an associated cost, then operational efficiencies would be better improved instead by reducing the need for such external heating. At steady state this is achieved by using both galvanostatic conditions within the stacks, i.e. a constant electrical current (constant amps), and by adopting thermoneutral voltages across the stack to avoid heat wastage in the stacks, as at a thermoneutral condition the electrolyser is in an adiabatic state, i.e. it is balanced energetically, which effectively means no heat is consumed or released.

[0130] In the prior art, it is known to use either constant voltages or constant currents on a stack, and then to control the current or the voltage, respectively, to maintain the stack at a substantially thermoneutral condition. This then allows the stack to avoid overcooling or overheating, as when at under-voltage (for a galvanostatic stack - i.e. constant current), the stack shows endothermic characteristics, and it thus cools the fluid (and likewise the operational temperature of the stack), whereby the fluid output temperature is lower than the fluid input temperature, whereas when at over-voltage (for a galvanostatic stack - i.e. constant current), the stack shows exothermic characteristics, and it thus heats the fluid (and likewise the operational temperature of the stack), whereby the fluid output temperature is higher than the fluid input temperature.

[0131] At steady state, a galvanostatic condition may be used for the stack, but fluctuates as necessary between thermoneutral conditions, over-voltage conditions and under-voltage conditions, in response to input fluid temperature control that aims to maintain a fluid input temperature equal to a fluid output temperature. This is done since the present inventors realised that it is relatively straightforward to measure temperature at an inlet and an outlet of the stack and thus to instead control the thermoneutral voltage automatically. In other words, at steady state the temperature delta between the fluid output temperature from the stack and the fluid input temperature for the stack is minimised, aiming for a zero delta. This then allows extended use of a galvanostatic condition for the stack, alongside a thermoneutral voltage condition, even while the stack, or at least one of the cell units therein, degrades.

[0132] Galvanostatic and thermoneutral (and galvanostatic thermoneutral) conditions such as those discussed above apply in steady state when the electrolyser system is at an operational temperature. Other steady state conditions or operating strategies, such as potentiostatic, endothermic or exothermic may also be used depending upon characteristics of the cell units and / or of input and exhaust fluids available or desired, respectively.

[0133] Other strategies are required in order to raise the electrolyser system to the operational temperature. Further, in cases where the heaters 150 and / or 151 are present, they may only have the capacity for a provision of trim heating at operational temperatures, e.g. to raise the heat of the input stream by 10-40 °C. Such heaters are unable to provide sufficient heat to the electrolyser system to warm the same from ambient to operational temperatures in a reasonable timeframe. However, provision of larger capacity heaters for the two heaters 150 and / or 151, to provide warm up heat, would result in oversized heaters for steady state operation, and thus unnecessary capex costs. Nonetheless, in each of the examples subsequently discussed, the heaters 150 and / or 151 - if in the form of trim heaters - may be used to assist warm up of the system when efficient to do so.

[0134] The abovementioned steady state operation is one mode of operation of an electrolyser system. Other modes of operation, including warm up, standby, and shutdown may be used with transitions therebetween. The electrolyser system may transition to a standby mode from a steady state (also referred to as a product-generating mode) or a warm up mode. As used herein, reference to supply / supplying or provide / providing to a volume also involves exhaust from that volume unless the context requires otherwise.

[0135] Referring next to Fig. 3, there is shown a control device or controller 400 for controlling an electrolyser cell stack of an electrolyser in an electrolyser system. The control device 400 comprises an input device 402 for receiving input from sensors 404 so as to determine at least one of: a stack operating voltage across the electrolyser stack(s), a stack operating current through the electrolyser stack(s), an inlet temperature at a fluid inlet, an outlet temperature at a fluid outlet and a common volume temperature. The control device 400 thus comprises at least one of: a voltage monitoring system 406 for determining a stack operating voltage across the electrolyser stack(s), a current monitoring system for determining a stack operating current through the electrolyser stack(s), an inlet temperature monitoring and / or control system 408 for determining an inlet temperature at the fluid inlet and an outlet temperature monitoring and / or control system 410 for determining an outlet temperature at the at least one fluid outlet of the electrolyser stack(s). These systems may utilize sensors and data transmission devices or wiring. The control device receives sensor data relating to each of these measurements. The control device may control the system by controlling valves for supply to and exhaust from each fluid volume and power supplies for non-fluid heating. A suitably programmed processor 412 and associated memory 414 is provided for processing such inputs.

[0136] The control device's inlet temperature monitoring and / or control system 408 may comprise an output device for controlling the identity and temperature of a fluid entering the electrolyser stack(s) at a fluid inlet. A current control system 416 is also provided for controlling a current supply to (and in some cases from) the electrolyser stack. As mentioned above, during normal operation this is adapted to provide a constant current to the electrolyser cell stack, but the current / voltage may be reduced or turned off to automatically shut down the stack or increased to warm-up the electrolyser stack(s).

[0137] The control device 400 may also control non-fluid heat sources (heaters and such like described above), recirculation loops, and temporary warm up configurations as described above, and may also control valves as described below.

[0138] In such a way, the control device 400 is adapted to control an electrolyser stack(s) and the electrolyser system 100, 101. An example of an electrochemical cell system may take the form of an electrolyser system. The electrolyser system may comprise an electrolyser assembly within an enclosure.

[0139] The electrolyser system may comprise a plurality of stacks 10 of electrolyser cell units (as an example, see Figure 4).

[0140] Connecting between stacks 10, there can also be provided a manifold for providing fluidic connection to the stacks 10 to the outside of the enclosure. An inside volume of the enclosure may be referred to as a common volume).

[0141] During operational use of the electrolyser system, the stacks 10, and thus the common volume, within which the stacks 10 are located, may be operating at a temperature of around 550 °C

[0142] Due to the use of the enclosure, which may take the form of a pressure vessel, the pressure vessel and its contents (including the manifolds and the stacks, can be referred to as a system. Likewise, each stack and each cell may be referred to as a system. The present invention concerns situations where there is an unexpected need to depressurise these systems. Disclosed above was the possibility of providing a control system to regulate the pressure of at least one or both of the fuel volume and the oxygen volume of the stacks, and optionally also to regulate the pressure in the common volume. This system can allow pressure increases and pressure decreases when working properly. However, there can be situations where operational control is diminished or disabled, such as if there is a power failure. The present invention thus provides a mechanism for controlling a depressurization of the fluid volumes in the event of such a problem - an emergency depressurization condition, for example.

[0143] Referring to Figure 5, a prior art system is shown. It comprises a fluid volume 60, a normally closed valve 108, a pressure regulator 84 (e.g. a back pressure regulator) and an exhaust 134. In normal operating conditions, the pressure regulator 84 is fluidical ly connected to the fluid volume 60 by controlling the normally closed valve 108 into an open state. Each of the valves described herein may be solenoid valves.

[0144] For controlling the pressure in the fluid volume 60, a pilot line 88 with an electronic pressure controller 98 is provided, which pilot line 88 is provided with pressurised fluid by a supply line 106. The pilot line 88 provides a reference pressure to the pressure regulator 84. That reference pressure is controlled by the electronic pressure controller 98. The pressure regulator 84 can thus control the pressure in the fluid volume 60 - itself supplied fluid at pressure by a fluid supply 70, 72 (for example a fuel or sweep gas supply 70, 72 in the case of an electrolyser cell unit), venting any over-pressure to the exhaust 134.

[0145] The fluidic connection between the pressure regulator 84 and the fluid volume 60, however, can be isolated via the normally closed valve 108 by de-powering the normally closed valve 108, which then reverts to its normally closed condition. To then depressurise the fluid volume 60, an emergency depressurization branch 71 is provided. This depressurization branch provides a flow restriction device 92 and a normally open valve 114. This emergency depressurization branch 71 is normally isolated from the exhaust 134 by the normally open valve 114 being closed (i.e. powered), but in the event of depowering the normally closed valve 108, this normally open valve 114 can also be depowered, which thus then opens it. This then connects the emergency depressurization branch 71 to the exhaust, via the flow restriction device 92 and the now open normally open valve 114 and the exhaust 134.

[0146] The provision of the emergency depressurization branch 71, however, complicates the pipework as it is an additional branch line. The present invention provides a more compact solution.

[0147] As shown in Fig. 6, in this embodiment of the present invention, there is still provided the fluid volume 60, supplied at pressure by a fluid supply 70, 72, and controlled at a pressure by a pressure regulator 84. However, the normally closed valve 108 has instead been moved to the pilot line 88. Furthermore, the emergency depressurisation branch 71 has been removed and the flow restriction device 92 has been moved to be a branch off the pilot line 88. That branch also has the normally open valve 114. A controller 138 is also shown for controlling the system, although a controller is likely also present in prior art systems. With this reconfigured system, the pilot line 88 still controls the pressure regulator 84 by providing a reference pressure thereto. That reference pressure is still controlled by the electronic pressure controller 98, fed pressurised fluid from the supply line 106. However, in this embodiment, the supply of fluid to the electronic pressure controller 98 can be controlled by the normally closed valve 108. By depowering the normally closed valve 108, the normally closed valve 108 will become closed, thus isolating the electronic pressure controller 98 from the supply of fluid from the supply line 106. When that happens, via the controller 138, for example, the normally open valve 114 will also be depowered, and thus will open. This then allows the pressure within the pilot line 88 to be depressurised through the flow restriction device 92 and the normally open valve 114 out to the exhaust 134. This thus then drops the reference pressure provided to the pressure regulator 84, thus also depressurising the fluid volume 60. The order of the flow restriction device 92 and the normally open valve 114 is reversible, but here is shown with the flow restriction device 92 upstream of the normally open valve 114. The flow restriction device may comprise an orifice, an orifice plate, an orifice aperture, a flow contraction, a screen, a perforated plate, or a through flow valve configured to provide a flow-rate restriction in a depressurisation condition. The fluid volume 60 is depicted as being in fluidic communication with the exhaust 134. It will be understood, however, that this exhaust may be fluidically isolated from the exhaust from the pilot line through the flow restriction device, and may instead be an exit of fluid product from the system. For example, for an electrolyser system, the fluid volume 60 may contain hydrogen product, which, even at reduced pressure, may want to be captured separately to the fluid exiting from the pilot line. Further, the electronic pressure controller 98 may have a separate vent line (not shown) controllable to vent fluid from the pilot line during normal operations, and thereby to reduce pressure in the pilot line, to somewhere other than the exhaust from the fluid volume 60.

[0148] The pressure regulator 84 may be a back pressure regulator. Pressure regulator 84 may be downstream of one or more heat exchangers configured to exchange heat between fluid exhausted from and fluid provided to the fluid volume 60. As a result, the pressure regulator 84 need not be configured to withstand elevated temperatures of an intermediate or high temperature electrolyser system, thereby improving its reliability and reducing cost.

[0149] Referring next to figure 7, a variation of the embodiment of figure 6 is shown. In this embodiment, a first tank 136 is also provided along the pilot line 88. This tank 136 provides an additional volume to the pilot line 88, whereby the time taken for the depressurisation of the pilot line 88 can be extended, thus slowing down also the depressurisation of the fluid volume 60. This can be beneficial for example when a rapid depressurisation of the fluid volume 60 is undesirable.

[0150] This embodiment additionally has both the first normally open valve 114 - now moved upstream of the flow restriction device 92, and a further normally open valve 142, also upstream of the flow restriction device 92. Including the further normally open valve 142 is optional, but it allows this system to be ready to adapt to systems having more than one fluid volumes. In this regard, referring next to figure 8, which shows such an embodiment - in which there are two fluid volumes 60, 62.

[0151] In this embodiment, the first fluid volume 60 is still provided with its pressure regulator 84 and a fluid supply 70, and is connected to an exhaust 134. Furthermore, the pilot line 88 for it has the first normally open valve 114 upstream of the flow restriction device 92, with the further normally open valve 142 also provided upstream of the flow restriction device 92, as per figure 7. It remains the case, however, that the positions of the flow restriction device 92 and the (in this case further) normally open valve 142 are reversible.

[0152] In this embodiment, the system is significantly modified versus the previous embodiments by the provision of a second fluid volume 62. This second fluid volume 62 is provided along its own pipeline that has a second pressure regulator 86, which connects to the exhaust 134. It also has its own fluid supply 72 and its pressure is controlled by a second pilot line 90. The second pilot line 90 is connected to the same supply line 106 as the first pilot line 88, but it comprises a second normally closed valve 130 and a second electronic pressure controller 102. It also has a second tank 124, which serves the same function as the first tank 136 in the first pilot line 88, but instead for the second pilot line 90. The second pilot line 90 also has its own branch line leading towards the flow restriction device 92, which branch line comprises a second normally open valve 132. In this embodiment, this second branch line connects to the first branch line (from the first pilot line 88) between the first normally open valve 114 and the further normally open valve 142, and thus upstream of the flow restriction device 92.

[0153] As with the earlier embodiments, it is again possible to reposition the flow restriction device 92 in this embodiment - by reversing the positions of the further normally open valve 142 and the flow restriction device 92. However, the second branch line would then instead connect between the first normally open valve 114 and the repositioned flow restriction device 92, i.e. still upstream of both the further normally open valve 142 and the flow restriction device 92. This embodiment can be adapted also simplified by the removal of either one of the first and second normally open valves 114, 132. However, it is preferred that both are provided for providing redundancy.

[0154] In this embodiment, during normal operating conditions the pilot lines 88, 90, input reference pressures into the first and second pressure regulators 84, 86 to control the pressure of the fluid within the first and second fluid volumes 60, 62. However, if a need to depressurise the first and second volumes 60, 62 arises, or if there is a power failure to the normally open and normally closed valves, this system can depressurise the first and second fluid volume 60, 62 in a controlled manner and such that the two volumes 60, 62 are maintained at substantially equal pressures relative to one another due to the connecting of the pilot lines 88, 90 together upstream of the flow restriction device 92 through which both pilot lines depressurise. This occurs since the normally closed valves 108, 130 will close, thus isolating the pilot lines 88, 90 from the supply line 106, whereas the normally open valves 114, 132, 142 will open, thus allowing the pilot lines 88, 92 to depressurise through the flow restriction device 92 and out to the exhaust 134. As that pressure reduces, this likewise controls the reference pressure provided to the pressure regulators 84, 86, thus allowing the fluid volume 60, 62 to likewise be depressurised in controlled conditions out to the exhaust 134.

[0155] In this embodiment, as mentioned above there is provided both the first tank 136 on the first pilot line 88 and the second tank 124 on the second pilot line 90, i.e. one for each of the pilot lines 88, 90. By providing these two tanks 136, 124, both pilot lines 88, 90 can depressurise more slowly than in figure 6, which in turn allows the two fluid volumes 60, 62 to depressurise more slowly. This can be particularly beneficial when there is more than one fluid volume to be depressurised as it ensures that the pressures of the two fluid volumes 60, 62 are maintained at the same pressure relative to one another during depressurisation. For example, where these two fluid volumes 60, 62 are the volumes either side of an electrolyte in a fuel cell unit or an electrolyser cell unit, maintaining the same pressure on either side of the electrolyte and other components which separate the two fluid volumes reduces stresses and strains across said components, and reduces the pressure differential which said components must be designed to withstand. As an electrolyte can be relatively fragile, as it is commonly made of a ceramic material, pressure imbalances either side of it greater than a given threshold are undesirable. With the slower depressurisation provided by virtue of the provision of the two tanks - one for each pilot line, pressure balance is maintained more accurately and the depressurisation is more gradual.

[0156] It will be understood that the tanks 124, 136 may be used in some cases and not in others, for example where sufficiently slow depressurization is achieved by other means (e.g., a relatively more restrictive flow restriction device or relatively higher viscosity fluid in the pilot line, or in cases where a relatively fast depressurization is acceptable). Further, a single tank may be used on only one of the pilot lines (i.e., only one of tanks 124, 136 of Fig. 8, and in the case of Fig. 9 below, only one of tanks 124, 136, 126). This is because in the depressurization condition the pilot lines are fluidically connected (e.g., by the normally open valves 114, 132). An example including a single tank is depicted in Fig. 10 as a variant on - and otherwise similar to - Fig. 8, in which the single tank 124 is on the first pilot line 90, but in a depressurization condition is in fluidic communication with both of pilot lines 88, 90. Such a single tank may have a larger volume than examples where each pilot line has a tank. In other cases there may be at least one tank, but fewer tanks than there are pilot lines. For example, where there is more than one tank, each tank may have a volume of at least 0.5 litres, up to a maximum of 10 litres, preferably between 1 and 5 litre, but where there is one tank its (or fewer tanks than pilot lines their) volume may be at least 1.5 litres, up to a maximum of 30 litres, preferably between 3 and 15 litres, more preferably between 11 and 20 litres.

[0157] Referring finally to figure 9, a variant of figure 8 is shown in which a third fluid volume 24 is provided. This third fluid volume 24 can be the common volume 24 of the pressure vessel shown in previous embodiments, the first fluid volume 60 may be a fuel (e.g., cathode for electrolysis) side 66 of a cell unit 82 or stack 10 thereof, or of multiple stacks 10 thereof, and the second fluid volume 62 may be an oxygen (e.g., anode for electrolysis) side 68 of such cell units 82 or stacks 10. All three fluid volumes 60, 62, 24 are thus separated from each other, yet need to be maintained at substantially balanced pressures to avoid or minimise stresses and strains at boundaries therebetween.

[0158] The first and second fluid volumes 60, 62 will be supplied fuel 143 (e.g. steam or carbon dioxide for electrolyser units or hydrogen or a hydrocarbon for a fuel cell unit) and sweep gas 144 (e.g. nitrogen or air), whereas the third fluid volume, being the common volume 24 within a pressure vessel, will be provided with common volume fluid 165, such as nitrogen or air.

[0159] The third fluid volume 24 is connected to a third pressure regulator 94 and then to the exhaust 134. The third pressure regulator 94 is controlled by a third pilot line 96, which is supplied fluid from the same supply line 106 as the other pilot lines 88, 90, and has a third normally closed valve 112, a third electronic pressure controller 104 and a third tank 126. The third electronic pressure controller 104 is also connected to the controller 138, as are the first and second electronic pressure controllers 98, 102. Similarly, the controller 138 is connected to the third normally closed valve 112 and a third normally open valve 149 provided on a further branch line from the third pilot line 96. That further branch line connects to the further normally open valve 142 and the flow restriction device 92, as per the other branch lines.

[0160] In this final embodiment, all three fluid volumes 60, 62, 24 can be depressurised in parallel using the same flow restriction device 92 by having the pilot lines 88, 90, 96 all fluidically connected together when the normally open valves are all open and the normally closed valves are all closed, i.e. when the power is turned off to those devices or they are so controlled by the controller 138.

[0161] The present invention has therefore been described with reference to various embodiments. The present invention is not limited to only the above examples. Other examples will be readily apparent to one of ordinary skill in the art without departing from the scope of the appended claims. These and other features of the present invention have been described above purely by way of example. Modifications in detail may be made to the invention within the scope of the claims.

Claims

CLAIMS1. A system comprising: at least two pressurisable fluid volumes which are not in fluidic communication with one another; at least two pressure regulators configured to regulate pressure in the respective at least two pressurisable fluid volumes; at least two pilot lines, each configured to provide a reference pressure to a respective one of the at least two pressure regulators; and a flow restriction device; wherein the system is configured such that in a depressurisation condition: the at least two pilot lines are in fluidic communication with one another and with the flow restriction device; and the pilot lines are configured to gradually depressurise by flow of fluid therein through the flow restriction device, thereby reducing the reference pressures for the at least two pressure regulators.

2. The system of claim 1, wherein the flow restriction device is configured to control the rate at which the pilot lines depressurise such that the pressurisable fluid volumes can depressurise with substantially matched or identical pressures at any point in time during the depressurisation process.

3. The system of any one of the preceding claims, wherein the system is configured to contain within the pressurisable fluid volumes fluids of differing fluidic properties.

4. The system of any one of the preceding claims, wherein there are three or more pressurisable fluid volumes, and the system is configured to contain within the pressurisable fluid volumes at least two fluids of differing fluidic properties.

5. The system of any one of the preceding claims, wherein each pressurisable fluid volume is provided with its own pressure regulator, its own pilot line and reference pressure, and all pilot lines, in the depressurisation condition, are configured to be in fluidic communication with one another and with the flow restriction device.

6. The system of any one of the preceding claims, wherein the at least two pilot lines are configured to contain fluids of similar fluidic properties.

7. The system of any one of the preceding claims, wherein the pilot lines are configured to be fluidically isolated from one another in operational conditions.

8. The system of any one of the preceding claims, wherein the pilot lines are configured to be individually pressure controlled by a respective electronic pressure controller.

9. The system of any one of the preceding claims, wherein each pilot line comprises at least one normally closed valve, and / or wherein each pilot line comprises at least one normally open valve.

10. The system of any one of the preceding claims, wherein in the decompression condition, the pilot lines are fluidically connected by opening at least one normally open valve and said normally open valve(s) is / are configured to be controlled to be closed in operational conditions.

11. The system of any one of the preceding claims, wherein each pilot line comprises a respective pressure controller which, in operational conditions, is configured to set the reference pressure in the respective pilot line for the pressure regulator of the allocated pressurisable fluid volume and is configured during operational conditions to be in fluidic communication with its supply line.

12. The system of any one of the preceding claims, wherein at least one of the pilot lines comprises at least one tank configured to retain a volume of supplied gas.

13. The system of claim 12, wherein the volume of each tank is at least 0.5 litres, up to a maximum of 10 litres, and optionally between 1 and 5 litres.

14. The system of any one of the preceding claims, wherein the flow restriction device is passive or unpowered.

15. The system of any one of the preceding claims, wherein the pressurisable system is an electrolyser system.

16. The system of claim 15, wherein the at least two pressurisable fluid volumes comprise first and second volumes of electrolyser cell units in the electrolyser system.

17. The system of claim 16, when dependent upon claim 4, wherein the third fluid volume is a common volume within a pressure vessel within which the cell units are positioned.

18. The system of claim 15, wherein there are two pressurisable fluid volumes, one of the fluid volumes being a common volume within a pressure vessel within which cell units of the electrolyser system are positioned, said common volume being in fluidic communication with one of a fuel side or an oxygen side of the cell units, and the other of the pressurisable fluid volumes being the other of the fuel side and the oxygen side of the cell units.

19. The system of any one of the preceding claims, wherein the pressure within the fluid volumes is maintained in normal operational conditions to be at least 0.5 barg, optionally at least 1 barg, optionally at least 1.5 barg, optionally between 1.5 barg and 3 barg, optionally no more than 10 barg, or optionally no more than 5 barg.

20. The system of any one of the preceding claims, wherein a controller is provided for the system, the controller being configured to, in operational conditions, control all normally open valves of the pilot lines to be in a closed state, and all normally closed valves of the pilot lines to be in an open state.

21. The system of claim 20, wherein the controller is configured to, in a depressurisation condition, control or release all normally open valves of the pilot lines to revert to an open state, and all normally closed valves of the pilot lines to a closed state.

22. A method of controlling a system according to any one of the preceding claims, comprising a controller for carrying out a process of decompressing the fluid volumes in a depressurisation condition using the flow restriction device to control depressurisation of the pilot lines.

23. The method of claim 22, wherein pressures in the fluid volumes are balanced such that a difference in pressure between the volumes is no more than 0.5 bar, optionally no more than 0.2 bar, optionally no more than 0.1 bar, optionally no more than 0.05 bar, and optionally no more than 0.01 bar.

24. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method as defined in claim 22 or claim 23.

25. A non-transitory computer-readable medium with instructions stored thereon, that when executed by a processor, perform or cause the processor to perform the method as defined in claim 22 or claim 23.

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