Hydrogen production unit equipped with a shutdown system, and method for shutting down such a unit

Abstract

The invention relates to a hydrogen production unit (200) comprising: a stack (102) of solid oxide cells, an air circuit (110), and a fuel circuit (120) passing through said stack (102); characterized in that said unit (200) is equipped with a shutdown system comprising: a neutral gas inlet (202) and outlet (204) for circulating a predetermined neutral gas through said stack, a safety gas inlet (206) and outlet (208) for circulating a safety gas through said stack (102), and a control module (210) for switching said stack (102) from the production configuration to the shutdown configuration. It also relates to a method for controlling such a unit. See Figure 2

Description

Title of the invention: Hydrogen production unit equipped with a shutdown system, and method for shutting down such a unit

[0001] The present invention relates to a unit for producing hydrogen by high-temperature electrolysis of water vapor provided with a system for stopping said unit. It also relates to a method for stopping such a unit.

[0002] The field of the invention is generally the field of the production of hydrogen by high-temperature electrolysis of water vapor, and in particular in a solid oxide electrolyzer. State of the art

[0003] There are currently various techniques for producing hydrogen. One of these techniques is the high-temperature electrolysis of water vapor in a solid oxide electrolyzer, SOEL (for "Solid Oxide Electrolyser" in English). In summary, water is heated to obtain water vapor at a temperature of around 150°C. The water vapor is introduced into a superheated electrolysis unit at a temperature between 700°C and 850°C and supplied with electric current to decompose the water vapor molecule H2O into molecules of H2 and O2 so as to obtain, at the outlet of said electrolysis unit, a flow of hydrogen H2 and a flow of oxygen O2 from a flow of water vapor.

[0004] A high-temperature steam electrolysis unit comprises a stack of solid oxide cells, also called a stack hereinafter, which constitutes the essential and also the most expensive component of said unit. Each electrolysis cell is in contact, on one side with a flow of air supplied by an air circuit and on the other with a flow, called fuel, the fuel being able to be either a steam-hydrogen mixture or a nitrogen-hydrogen mixture. The need to maintain the operating conditions of the stack (pressure, composition of the fluids and temperature) in a precise envelope is essential, any deviation from this envelope being able to lead to damage or even destruction of the cells making up each stack. By way of example, and in a non-exhaustive manner: - maintaining a pressure differential on either side of each cell is essential, and too high a pressure differential (positive or negative) can mechanically damage the cells. This failure to maintain the pressure on each side and the pressure differential may be due to a problem with the relevant control loops, a problem with the air supply (flow, pressure), or a problem with the fuel supply (flow, pressure); - when the cells produce hydrogen (in this case the fuel is a

[0005]

[0006]

[0007]

[0008]

[0009] steam-hydrogen mixture), too low a steam flow or even a steam cut-off leads to short-term destruction of the cell (a phenomenon known as “steam starvation”); - if the proportion of hydrogen in the inlet fuel flow is too low, then we observe re-oxidation phenomena which are harmful to the functioning of the cells; - if the humidity level of the air supplied to the stack (air side) is too high, unacceptable cell degradation can also be observed. Thus, for all process deviation situations that could affect the integrity of the stacks (and therefore the cells), there is a need for a solution that allows a shutdown, in particular an emergency shutdown, of the electrolysis unit without damaging the said unit and without presenting any risk. An aim of the present invention is to remedy at least one of the aforementioned drawbacks. Another aim of the invention is to provide an effective solution for quickly and without damage stopping a high temperature water vapor electrolysis unit. Another aim of the invention is to propose an effective solution for carrying out an emergency shutdown of a hydrogen production unit by electrolysis of high-temperature water vapor. Statement of the invention The invention proposes to achieve at least one of the aforementioned aims by a unit for producing hydrogen by high-temperature electrolysis of water vapor, said unit comprising: - a stack of solid oxide cells, - a circuit, called an air circuit, passing through said stack, and comprising a air inlet and an oxygen-enriched air outlet, in a hydrogen production configuration of said stack, and - a circuit, called the fuel circuit, passing through said stack, comprising a water vapor inlet and a water vapor outlet enriched with hydrogen, in said production configuration. According to the invention, the hydrogen production unit is equipped with a system for shutting down said unit, said shutting down system comprising: - an inlet and an outlet for neutral gas, provided on the air circuit on either side of said stack, for circulating a predetermined neutral gas in said stack, in a stop configuration of said stack, - a safety gas inlet and outlet, provided on the fuel circuit of on either side of said stack, to circulate a predetermined safety gas in said stack, in the shutdown configuration, and - a control module for switching said stack from the production configuration to the shutdown configuration.

[0010] Thus, the invention proposes a unit for producing hydrogen by high-temperature electrolysis of water vapor which is equipped with a system for stopping said unit.

[0011] The shutdown system makes it possible to inject, on the one hand, a neutral gas into the air circuit and, on the other hand, a safety gas into the fuel circuit: thus, it is possible to maintain a pressure balance, as well as conditions preventing re-oxidation of the cells, in the stack of cells and in particular on either side of each cell: this makes it possible to preserve the integrity of the cells and therefore not to damage the stack of cells.

[0012] In addition, the injection of the neutral gas into the air circuit and the safety gas into the fuel circuit allows a “drying of the cells” making it possible to very significantly reduce the presence of oxygen molecules (present in the steam but also the air) causing a re-oxidation of the cells in a non-reducing environment (i.e. not sufficiently rich in hydrogen).

[0013] Furthermore, and above all, the shutdown system equipping the hydrogen production unit can be used to carry out an emergency shutdown of said unit, for example in the event of an incident on the air circuit or on the fuel circuit. Such an emergency shutdown can be triggered very quickly in the event of an incident because the shutdown system is connected to the air and fuel circuits directly, and at any time.

[0014] By "air circuit" is meant a circuit supplying a first flow, which is generally air, to the stack of cells. This first flow is charged with O2 molecules produced during the electrolysis of water vapor in the stack so that the air circuit evacuates from said stack a first flow enriched in oxygen.

[0015] The air circuit comprises an inlet duct bringing the first flow towards the stack, a path within the stack, and an outlet duct discharging the first oxygen-enriched flow from said stack.

[0016] The air circuit comprises an inlet, provided on the inlet duct, for the first flow and used during the production phase. The inlet may preferably be provided with one or more valves making it possible to authorize, prohibit, and possibly adjust, the passage of flow through said inlet.

[0017] The air circuit comprises an outlet, provided on the outlet duct, for evacuating the first oxygen-enriched flow during the production phase. The outlet may be provided with one or more valves for authorizing, prohibiting, and possibly adjusting, the passage of flow through said outlet.

[0018] By “fuel circuit” is meant a circuit providing a second flow comprising water vapor, H2O, and hydrogen, H2, typically in a respective 90% / 10% molar distribution, to the cell stack. The water vapor molecules are broken in the stack during the electrolysis reaction, which produces hydrogen molecules, H2, and O2 molecules. The O2 molecules pass into the air circuit through each cell and enrich the first flow with oxygen. The H2 molecules remain in the fuel circuit and enrich the second flow with H2. Thus, the fuel circuit evacuates a second flow enriched with H2 from the stack.

[0019] The fuel circuit comprises an inlet conduit bringing the second flow towards the stack, a path within the stack, and an outlet conduit discharging the second hydrogen-enriched flow from said stack.

[0020] The fuel circuit comprises an inlet, provided on the inlet pipe, for the second flow and used during the production phase to supply the second flow to the stack. According to embodiments, the inlet may comprise several sub-inlets, each used to inject a component of the second flow, when the latter is a mixture of several gases. Thus, the inlet of the fuel circuit may for example comprise a water vapor sub-inlet, an H2 sub-inlet and possibly a safety gas sub-inlet. The inlet, or at least one sub-inlet where appropriate, may preferably be provided with one or more valves making it possible to authorize, prohibit, and possibly adjust the passage of flow through said inlet, or at least one sub-inlet respectively.

[0021] The fuel circuit comprises an outlet, provided on the outlet pipe, for discharging the second H2-enriched stream during the production phase. According to embodiments, the outlet may comprise several sub-outlets, each used to recover a component of the second hydrogen-enriched stream. Thus, the outlet of the fuel circuit may for example comprise a water vapor sub-outlet for recovering the residual water vapor in the second hydrogen-enriched stream, an H2 sub-outlet for recovering the H2 present in the second stream, etc. The outlet, or at least one sub-outlet where appropriate, may preferably be provided with one or more valves for authorizing, prohibiting, and possibly adjusting, the passage of stream through said outlet, or at least one sub-outlet respectively.

[0022] By "production configuration" is meant a configuration in which the electrolysis reaction takes place in the stack of cells, so that said stack generates hydrogen by high-temperature electrolysis of water vapor.

[0023] By "stop configuration" is meant a configuration in which the electrolysis reaction is stopped, or at least in the process of being stopped, so that the production of hydrogen is stopped, starting from a production configuration of the hydrogen production unit.

[0024] By "start-up configuration" is meant a configuration in which the electrolysis reaction is triggered, or at least in the process of being triggered, starting from a shutdown configuration of the hydrogen production unit.

[0025] According to embodiments, the neutral gas inlet may comprise at least one valve for regulating the passage of neutral gas.

[0026] Thus, it is possible to actuate this valve to authorize or not the passage of the neutral gas into the air circuit, and possibly adjust it. In other words, it is possible to trigger the hydrogen production shutdown phase by actuating this valve to inject the neutral gas into the air circuit, which can be done simply and quickly. Above all, the actuation of the valve can be done automatically, upon detection of an incident on the air circuit and / or on the fuel circuit, which allows an emergency shutdown to be carried out.

[0027] The control valve equipping the neutral gas inlet on the air circuit may be a normally open valve. Thus, the valve allows the passage of neutral gas into the air circuit in its normal state and must be closed otherwise.

[0028] According to embodiments, the neutral gas inlet may comprise a pressure regulator for regulating the pressure of the neutral gas in the air circuit.

[0029] Thus, it is possible to control and adjust the pressure of the neutral gas in the air circuit to avoid any pressure drift in the air circuit during the shutdown phase and to avoid degradation of the cell stack.

[0030] According to an exemplary embodiment, the pressure regulator can be configured to ensure a pressure of 10 mbarg at the outlet of the air circuit and a pressure of Ibarg at the inlet of the air circuit. Of course, these values ​​are given as an indicative example and are in no way limiting.

[0031] According to embodiments, the neutral gas outlet may comprise at least one valve for regulating the passage of neutral gas.

[0032] The control valve equipping the neutral gas outlet on the air circuit may be a normally open valve so that it allows the neutral gas to exit the air circuit in its normal state and must be closed otherwise.

[0033] According to embodiments, the shutdown system may further comprise a source of neutral gas connected to the neutral gas inlet.

[0034] Such a source of neutral gas may be a reservoir of neutral gas.

[0035] Such a source of neutral gas may be at ambient pressure. Alternatively, Preferably, the neutral gas source may be at a pressure greater than or equal to the desired neutral gas pressure in the air circuit. Such a neutral gas source may comprise, or be, one or more neutral gas cylinders.

[0036] Alternatively, the shutdown system of the hydrogen production unit according to the invention may not include a source, or reservoir, of neutral gas, in particular particularly when the site on which said hydrogen production unit is located is already equipped with a source of neutral gas. In this case, the neutral gas inlet is connected directly, or via another device, to said source of neutral gas equipping said site.

[0037] According to embodiments, the safety gas inlet may comprise at least one valve for regulating the passage of safety gas.

[0038] Thus, it is possible to actuate this valve to authorize or not the passage of the safety gas into the fuel circuit, and possibly adjust it. In other words, it is possible to trigger the hydrogen production shutdown phase by actuating this valve to inject the safety gas into the fuel circuit, which can be done simply and quickly. Above all, the actuation of the valve can be done automatically, upon detection of an incident on the air circuit and / or on the fuel circuit, which makes it possible to carry out an emergency shutdown of the hydrogen production unit.

[0039] The control valve equipping the safety gas inlet on the fuel circuit may be a normally open valve. Thus, the valve allows the passage of safety gas into the fuel circuit in its normal state and must be closed otherwise.

[0040] According to embodiments, the safety gas inlet may comprise a pressure regulator for regulating the pressure of the safety gas in the fuel circuit.

[0041] Thus, it is possible to control and adjust the pressure of the safety gas in the fuel circuit to avoid any pressure drift in the fuel circuit during the shutdown phase and to avoid degradation of the cell stack.

[0042] According to an exemplary embodiment, the pressure regulator can be configured to ensure a pressure of 10 mbarg at the outlet of the fuel circuit and a pressure of Ibarg at the inlet of the fuel circuit. Of course, these values ​​are given as an indicative example and are in no way limiting.

[0043] According to embodiments, the safety gas outlet may comprise at least one valve for regulating the passage of safety gas.

[0044] The control valve equipping the safety gas outlet on the fuel circuit may be a normally open valve so that it allows the safety gas to exit from the fuel circuit in its normal state and must be closed otherwise.

[0045] According to embodiments, the shutdown system may further comprise a safety gas source connected to the safety gas inlet.

[0046] Such a safety gas source may be a safety gas tank.

[0047] The safety gas source may be at ambient pressure. Alternatively, the safety gas source may be at a pressure greater than or equal to the desired safety gas pressure in the fuel system. The safety gas source may include, or be, one or more safety gas cylinders.

[0048] Alternatively, the shutdown system of the hydrogen production unit according to the invention may not include a source, or reservoir, of safety gas, in particular when the site on which said hydrogen production unit is located is already equipped with a source of safety gas. In this case, the safety gas inlet is connected directly, or via another device, to said source of safety gas equipping said site.

[0049] Of course, the neutral gas inlet and / or the neutral gas outlet can be equipped with a pressure sensor and / or a flow sensor.

[0050] Of course, the safety gas inlet and / or the safety gas outlet can be equipped with a pressure sensor and / or a flow sensor.

[0051] According to non-limiting embodiments, the neutral gas may be, or may comprise, nitrogen. Of course, another gas which is neutral with respect to the high-temperature electrolysis of water vapor may be used.

[0052] According to embodiments, the safety gas can be any type of non-explosive gas in a configuration for producing hydrogen by high-temperature electrolysis.

[0053] According to non-limiting embodiments, the safety gas may be an N2 / H2 mixture with a proportion of H2 preventing re-oxidation of the cells, in particular a proportion of H2 less than or equal to 5%, in particular less than or equal to 4% of H2, for example less than or equal to 1%. Of course, another safety gas with respect to high-temperature electrolysis of water vapor may be used.

[0054] The control module can be any type of electronic and / or electropneumatic and / or electromechanical device.

[0055] The control module can for example be a state machine.

[0056] The control module may comprise one or more inputs receiving one or several input values, or input signals, chosen from the following values / signals: - at least one pressure value / signal in the air circuit, and / or at least one pressure value / signal in the fuel circuit; - at least one temperature value / signal in the air circuit, and / or at least one temperature value / signal in the fuel circuit; - at least one temperature value / signal in the stack, and / or at least one pressure value / signal in the stack; - at least one status value / signal signaling the operating status of at least one valve of the air circuit, in particular at least one valve equipping the inlet, in the air circuit, of the first flow and / or at least one valve equipping the outlet, of the air circuit, of the first oxygen-enriched flow; - at least one status value / signal signaling the operating status of at least one valve of the fuel circuit, in particular at least one valve equipping the inlet, in the fuel circuit, of the second flow and / or at least one valve equipping the outlet, from the fuel circuit, of the second flow enriched in hydrogen.

[0057] According to embodiments, the control module can be arranged to detect an incident on the air circuit and / or an incident on the fuel circuit, and trigger the shutdown configuration.

[0058] Incident detection can be performed based on at least one input data item received by the control module. In particular, incident detection can be performed based on at least one input data item relating to the pressure in each of the circuits, or the state of a valve in the air circuit and / or the state of a valve in the fuel circuit. More generally, incident detection can be performed based on one or more of the input data items listed above.

[0059] The control module can generate at least one output data, or at least one output signal, and in particular: - at least one data item, or at least one output signal, for controlling at least one valve, and in particular each valve, installed on the air circuit, and / or - at least one data item, or at least one output signal, to control at least one valve, and in particular each valve, installed on the fuel circuit.

[0060] According to embodiments, the control module can be configured, or programmed, to carry out a shutdown phase in order to switch the hydrogen production unit from the production configuration to the shutdown configuration.

[0061] The stopping phase may comprise a triggering step comprising the following steps carried out in parallel: - opening of the neutral gas inlet and the neutral gas outlet on the air circuit, and of the safety gas inlet and the safety gas outlet on the fuel circuit, and - closing of other air and fuel circuit inlets and outlets.

[0062] Preferably, these steps can be carried out simultaneously.

[0063] These steps can alternatively be carried out in a short period of time, for example less than or equal to 5 seconds, more particularly 2 seconds.

[0064] At the end of the triggering step, the air circuit is traversed only by the neutral gas and the fuel circuit is traversed only by the safety gas. Thus, the respective pressure of each of the circuits, and the relative pressure of the two circuits between them, is ensured by the neutral gas and the safety gas. In addition, these gases allow to terminate, or at least begin to stop, the electrolysis reaction taking place in the cell stack.

[0065] According to embodiments, the control module can be configured, or programmed, to carry out, during the shutdown phase, a step of purging the hydrogen production unit according to the invention, and in particular the stack of cells.

[0066] The purging step may comprise the following steps: - keeping open the neutral gas inlet and the neutral gas outlet on the air circuit, and the safety gas inlet and the safety gas outlet on the fuel circuit, and - keeping the other inlets and outlets of the air and fuel circuits closed; for a predetermined duration, and / or until a predetermined pressure is reached.

[0067] The purging step makes it possible to purge, with the neutral gas, the air circuit of the oxygen found in said air circuit. Indeed, after the start of the shutdown phase, certain cells may not yet be completely shut down and produce hydrogen before the electrolysis reaction stops completely, which still generates oxygen which must be purged.

[0068] The purging step makes it possible to purge, with the safety gas, the fuel circuit of the hydrogen, or water vapor, found in said fuel circuit. Indeed, after the start of the shutdown phase, certain cells may not yet be completely shut down and produce hydrogen before the electrolysis reaction stops completely, which still generates hydrogen that must be purged. In addition, there may still be water vapor in the fuel circuit: this residual water vapor must be purged otherwise it can damage the electrolysis cells.

[0069] The purging step can be carried out for a predetermined duration, for example 30 minutes. This duration can vary from one unit to another, for example depending on the size of the stack of cells or the power of the hydrogen production unit.

[0070] The purging step can be carried out until a predetermined pressure is reached in the air circuit, and / or in the fuel circuit.

[0071] According to embodiments, the control module can be configured, or programmed, to carry out, during the shutdown phase, a step of cooling the hydrogen production unit according to the invention, and in particular the stack of cells.

[0072] This cooling step may comprise the following steps: - keeping the neutral gas inlet on the air circuit and the safety gas inlet on the fuel circuit open, - closing the neutral gas outlet on the air circuit and the safety gas outlet on the fuel circuit, and - keeping the other inlets and outlets of the air and fuel circuits closed; for a predetermined period, and / or until the stack temperature reaches below a predetermined threshold.

[0073] This cooling step makes it possible to lower the temperature of the production unit, and in particular the stack of cells, while compensating for intrinsic gas losses in the stack of cells.

[0074] The cooling step can be carried out for a predetermined duration, for example 2 hours. This duration can vary from one unit to another, for example depending on the size of the stack of cells or the power of the hydrogen production unit according to the invention.

[0075] The cooling step can be carried out until the temperature of the stack of cells is less than or equal to a threshold temperature, for example 200°C.

[0076] According to another aspect of the present invention, there is proposed a method for controlling a hydrogen production unit according to the invention, said method comprising a shutdown phase for switching the hydrogen production unit according to the invention from the production configuration to the shutdown configuration.

[0077] The shutdown phase may comprise the steps described above with reference to the control module, as well as any alternatives or features described in connection with each of said steps.

[0078] In particular, the stopping phase may comprise a triggering step comprising the following steps carried out in parallel, and preferably simultaneously: - opening of the neutral gas inlet and the neutral gas outlet on the air circuit, and of the safety gas inlet and the safety gas outlet on the fuel circuit, and - closing of other air and fuel circuit inlets and outlets.

[0079] According to embodiments, the shutdown phase may comprise a purging step comprising the following steps: - keeping open the neutral gas inlet and the neutral gas outlet on the air circuit, and the safety gas inlet and the safety gas outlet on the fuel circuit, and - keeping the other inlets and outlets of the air and fuel circuits closed; for a predetermined period, and / or until a predetermined pressure is reached in the stack of cells.

[0080] According to embodiments, the stopping phase may comprise a cooling step comprising the following steps: - keeping open the neutral gas inlet on the air circuit and the inlet of safety gas on the fuel circuit, - closing of the neutral gas outlet on the air circuit and the safety gas outlet on the fuel circuit, and - keeping the other inlets and outlets of the air and fuel circuits closed; for a predetermined period, and / or until the stack temperature reaches below a predetermined threshold. Description of figures and embodiments

[0081] Other advantages and characteristics will appear on examining the detailed description of non-limiting embodiments, and the appended drawings in which: - [Fig.l] is a schematic representation of a non-limiting example of a state-of-the-art hydrogen production unit; and - [Fig.2] is a schematic representation of a non-limiting exemplary embodiment of a hydrogen production unit according to the invention; - [Fig. 3] is a schematic representation of another non-limiting example of embodiment of a hydrogen production unit according to the invention; and - [Fig.4] is a schematic representation of a non-limiting example of an embodiment of a method according to the invention.

[0082] It is understood that the embodiments which will be described below are in no way limiting. In particular, it will be possible to imagine variants of the invention comprising only a selection of characteristics described below isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one preferably functional characteristic without structural details, or with only a part of the structural details if it is this part which is only sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

[0083] In particular, all the variants and all the embodiments described can be combined with each other if nothing prevents this combination from a technical point of view.

[0084] In the figures and in the remainder of the description, the elements common to several figures retain the same reference.

[0085] [Fig.l] is a schematic representation of a non-limiting example embodiment of a hydrogen production unit, from the state of the art.

[0086] Unit 100 of [Fig.l] produces hydrogen by high-temperature electrolysis of water vapor, and in particular electrolysis of water vapor at a temperature between 700°C and 850°C.

[0087] The unit 100 for producing hydrogen by high-temperature electrolysis of water vapor comprises a stack 102 of electrolysis cells. In particular, each electrolysis cell is a solid oxide electrolysis cell. In particular, the unit 100 is a solid oxide electrolyzer, or SOEL for "Solid Oxide Electrolyzer" in English.

[0088] The stack 102 of electrolysis cells may be a vertical stack or a horizontal stack. The stack 102 may comprise a given number of electrolysis cells, and in particular 50 electrolysis cells stacked with each other with interconnectors arranged between two adjacent cells. The stack is powered by water vapor and an electric current. At the electrolysis cells, the water vapor molecules are broken, which makes it possible to produce hydrogen, and in particular dihydrogen H2, and oxygen and in particular dioxygen, O2.

[0089] The stack 102 is arranged in an enclosure 104, called a hotbox, maintained at high temperature, in particular at a temperature between 700°C and 850°C.

[0090] The enclosure 104 may comprise heat exchangers, and in particular two heat exchangers 106 and 108 for heating the flows entering the stack and recovering the heat from the flows leaving the stack.

[0091] The unit 100 further comprises a first circuit 110, called the air circuit, providing an air flow to the stack 102. The air flow enters the air circuit 110 through an air inlet 112, then passes through the air circuit 110 via the stack 102. Upon passing the stack 102, the air flow circulating in the air circuit 110 is enriched with the O2 molecules produced during the electrolysis. The oxygen-enriched air flow leaves the air circuit through an air outlet 114.

[0092] In the example shown in [Fig.l], the air inlet 112 of the air circuit 110 is equipped with: - an isolation valve 116i. This isolation valve 116i is a normally closed valve 116. During operation of the production unit, the valve 116i is kept open, for example, by means of a pneumatic circuit controlling the opening of said valve 116i; - a flow control valve 118i. This flow control valve 1181 is a normally open valve. In the example of [Fig.l], this flow control valve 1181 is arranged between the isolation valve 116i and the hotbox 104. This valve 1181 has the function of controlling, and / or adjusting, the flow rate of the flow entering the stack via the air circuit.

[0093] The air outlet 114 of the air circuit 110 is equipped with: - an isolation valve 1162. This isolation valve 1162 is a normally closed valve. During operation of the production unit, the valve 1162 is kept open for example by means of a pneumatic circuit controlling the opening of said valve 1162; - a control valve 1182 controlling the back pressure. This control valve 1182 is a normally open valve. In the example of [Fig.l], this back pressure control valve 1182 is arranged between the isolation valve 1162 and the hotbox 104.

[0094] The unit 100 further comprises a second circuit 120, called the fuel circuit, supplying a second stream comprising water vapor, H2OV, to the stack 102. The second stream enters the fuel circuit 120 through a fuel inlet 122, then passes through the fuel circuit 120 via the stack 102. Upon passing through the stack 102, the second stream circulating in the fuel circuit 120 is enriched with the H2 molecules produced during the electrolysis. The second stream enriched with hydrogen leaves the fuel circuit 120 through an air outlet 124.

[0095] In the example shown in [Fig.l], the fuel inlet 122 comprises several inlets, or sub-inlets. The fuel inlet 122 comprises: - a first sub-inlet 122i to inject water vapor H2OV into the fuel circuit 120: it is this water vapor which will be electrolyzed to produce hydrogen; - a second sub-input 1222 for injecting a quantity of hydrogen H2 into the fuel circuit 120: the hydrogen injected into the fuel circuit 120 mixes with the water vapor and allows the electrochemical reaction to be carried out under good conditions; - a third sub-input 1223 for injecting a quantity of safety gas, SG (for “Safety Gas” in English), into the fuel circuit 120: the SG injected into the fuel circuit 120 mixes with the water vapor, and where appropriate with the hydrogen. Thus, the second flow injected into the fuel circuit 120 via the fuel inlet 122 may have a different composition depending on the state in which the production unit 100 is located.

[0096] Indeed, depending on the state of the production unit, the composition of the flow supplied to the fuel inlet 122 may differ: - in a state, called "Hot standby state", in which the enclosure is at operating temperature but the stack is not supplied with electrical current, no H2 is produced and the stacks are kept at temperature. In this state, it is preferable to supply the stack with safety gas with a minimum of 4% H2 to avoid re-oxidation phenomena; - in an electrolysis operating state, the stack is at operating temperature and is supplied with current, the gas flow supplied to the fuel inlet is a mix of water vapor and H2.

[0097] In the example shown in [Fig.l], the fuel inlet 122 has three inlets. Alternatively, the fuel circuit 120 may include a different number of sub-inlets.

[0098] In the example shown in [Fig.l], each of the fuel sub-inlets 122r1223: - an isolation valve 1163. This isolation valve 1163 is a normally closed valve. During operation of the production unit, the valve 1163 is kept open for example by means of a pneumatic circuit controlling the opening of said valve 1163; - a flow control valve 1183. This flow control valve 1183 is a normally open valve. In the example of [Fig.l], this flow control valve 1183 is arranged between the isolation valve 1163 and the hotbox 104. This valve 1183 has the function of controlling, and / or adjusting, the flow rate of the flow entering the stack via the fuel circuit.

[0099] In the example shown in [Fig.l], the fuel outlet 124 comprises several outlets, or sub-outlets. The fuel outlet 124 comprises: - a first sub-outlet 124i to recover water vapor mixed with hydrogen H2; - a second sub-exit 1242 to recover the SG.

[0100] Each of the sub-outputs 124i-1242 of the fuel circuit 120 is equipped with: - an isolation valve 1164. This isolation valve 1164 is a normally closed valve. During operation of the production unit, the valve 1164 is kept open, for example, by means of a pneumatic circuit controlling the opening of said valve 1164; - a control valve 1184 controlling the back pressure. This control valve 1184 is a normally open valve. In the example of [Fig.l], this back pressure control valve 1184 is arranged between the isolation valve 1164 and the hotbox 104.

[0101] The unit 100 of [Fig.l] does not include a shutdown system for performing a shutdown of said unit 100, and in particular an emergency shutdown in the event of an incident in the air circuit 110 or in the fuel circuit 120. For example, a malfunction of the air circuit 110 or of the fuel circuit 120 may disrupt the pressure balance in the stack 102, and therefore damage the cells in the stack 102. However, the unit 100 does not include any means for intervening on said unit 100 and stopping it when such a malfunction occurs.

[0102] [Fig.2] is a schematic representation of an exemplary embodiment not limiting of a hydrogen production unit according to the invention.

[0103] Unit 200 of [Fig.2] produces hydrogen by high-pressure electrolysis water vapor temperature, and in particular electrolysis of water vapor at a temperature between 700°C and 850°C.

[0104] Unit 200 of [Fig.2] comprises all the elements of unit 100 of [Fig.l].

[0105] Furthermore, and unlike unit 100 of [Fig.l], unit 200 of [Fig.2] is equipped with a system for stopping said unit 200.

[0106] The stopping system comprises: an inlet 202 to inject a predetermined neutral gas, NG (for “Neutral Gas » in English), in the air circuit 110, and an outlet 204 of neutral gas NG for evacuating the neutral gas NG from the air circuit 110; provided on the air circuit 110 on either side of the stack 102. It should be noted that, preferably, the inlet and outlet 202 and 204 of the neutral gas NG are dedicated to the neutral gas NG and are not used for other flows.

[0107] The stopping system further includes: an input 206 for injecting a predetermined safety gas, SG (for "Security Gas" in English) in the fuel circuit 120, and a safety gas outlet 208 SG for evacuating the safety gas SG from the fuel circuit 120; provided on the fuel circuit 120 on either side of the stack 102. It should be noted that, preferably, the inlet and outlet 222 and 224 of the safety gas SG are dedicated to the safety gas SG and are not used for other flows.

[0108] The shutdown system further comprises a control module 210 for triggering a shutdown of hydrogen production, and switching the unit 200 and in particular the stack 102 from a hydrogen production configuration to a hydrogen production shutdown configuration.

[0109] The NG 202 neutral gas inlet is equipped with: of a 212i pressure regulator; and of a normally open 214i isolation valve. In the non-limiting example shown in [Fig.2], the isolation valve 214i is positioned between the pressure regulator 212i and the stack 102.

[0110] The NG 204 neutral gas outlet is equipped with: of a normally open 2142 isolation valve, and optionally, a manual valve 216X which can be manipulated in the event of a power failure to control the isolation valves 214i and 2142. This manual valve 216i is preferably in the open state and can be closed manually if necessary. In the non-limiting example shown in [Fig.2], the isolation valve 2142 is positioned between the optional manual valve 216i and the stack 102.

[0111] Each of the isolation valves 214i and 2142 is, as indicated, a normally open valve such that in the absence of a command, it is in the open state. Their closure requires the receipt of a closing command, for example a pneumatic command or an electrical command.

[0112] The SG 206 safety gas inlet is equipped with: - a pressure regulator 2122; and - a normally open 2143 isolation valve. In the non-limiting example shown in [Fig.2], the isolation valve 2143 is positioned between the pressure regulator 2122 and the stack 102.

[0113] The SG 208 safety gas outlet is equipped with: - a normally open 2144 isolation valve, and - optionally, a manual valve 2162 which can be operated in the event of a power failure to control the isolation valves 2143 and 2144. This manual valve 2162 is preferably in the open state and can be closed manually if necessary. In the non-limiting example shown in [Fig.2], the isolation valve 2144 is positioned between the optional manual valve 2162 and the stack 102.

[0114] Each of the isolation valves 2143 and 2144 is, as indicated, a normally open valve so that in the absence of a command, it is in the open state. Their closure requires the receipt of a closing command, for example a pneumatic command or an electrical command.

[0115] The shutdown system further comprises, as indicated above, a control module 210 for triggering a shutdown of hydrogen production, and switching the unit 200 and in particular the stack 102 from a hydrogen production configuration to a hydrogen production shutdown configuration.

[0116] The control module 210 can be connected directly or indirectly to the valves 116, 118 and 214, and / or to the regulators 212, equipping the inlets and outlets of the air circuit 110 and the fuel circuit 120.

[0117] The control module 210 is configured, or programmed to carry out a shutdown phase allowing the hydrogen production unit 200 to be switched from a hydrogen production configuration to a hydrogen production shutdown configuration. In other words, the control module 210 makes it possible to control a shutdown of the unit 200, and in particular of the stack 102.

[0118] In particular, the control module 210 is configured to carry out the following steps.

[0119] First of all, during a step of triggering the stopping phase, the control module 210 commands, preferably simultaneously: - the opening • valve 214i of the neutral gas inlet NG 202, • valve 2142 of the neutral gas outlet NG 204, • valve 2143 of the safety gas inlet SG 206, and • the SG 208 safety gas outlet valve 2144; and - closing of valves 116rl 164 and 1181-1184 of all other inlets and outlets 112, 114, 122 and 124 of the air 110 and fuel 120 circuits.

[0120] Thus, the air circuit 110 is traversed only by the neutral gas NG and the fuel circuit 120 is traversed only by the safety gas SG. The respective pressure of each of the circuits 110 and 120 is adjusted by the pressure regulators 212i and 212 2, so as to obtain a substantially identical pressure in each of the circuits, in particular in the stack 102.

[0121] During a purge step, the control module 210 controls: - maintaining in the open position the valves 214r2142 of the inlet 202 and the outlet 204 of neutral gas NG, and the valves 2143-2144 of the inlet 206 and the outlet 208 of safety gas SG, and - keeping all other valves in the closed position; for a predetermined period, for example 30 minutes. During this period the stack 102 is purged, for example of residual oxygen and residual water vapor present in said stack 102.

[0122] Then, during a cooling step, the control module 210 controls: - the maintenance in the open position of the valve 214i equipping the inlet 202 of neutral gas NG, and of the valve 2143 equipping the inlet 206 of safety gas SG, - the closing of the valve 2142 equipping the outlet 204 of neutral gas NG, and of the valve 2144 equipping the outlet 208 of safety gas SG, and - keeping all other valves in the closed position; until the temperature of the stack 102 is less than or equal to a threshold temperature, below which the risk of re-oxidation no longer exists, for example below 250°C.

[0123] After the cooling step, the stack 102 and more generally the hydrogen production unit 200 is in the shutdown configuration.

[0124] The shutdown system can be used to shut down the unit 200 when it is desired to stop hydrogen production, without there being an incident or malfunction.

[0125] Above all, the shutdown system can be used to carry out an emergency shutdown of the unit 200, for example in the event of an incident occurring on the air circuit or on the fuel circuit which could break the pressure balance between the two circuits, in particular at the level of the stack 102, and therefore cause degradation of the stack 102.

[0126] The shutdown phase can be initiated manually by an operator.

[0127] Alternatively, the shutdown phase may be initiated automatically following the detection of an incident. According to embodiments, the control module 210 can be configured to detect an incident based on at least one data item, or at least one input signal relating to: - the operating state of the valve(s) equipping at least one, in particular each, inlet of the air circuit 110, and / or each outlet of the air circuit 110; - the operating state of the valve(s) equipping at least one, in particular each, inlet of the fuel circuit 120, and / or each outlet of the fuel circuit 120; - the pressure in the air circuit 110, and / or - the pressure in the fuel circuit 120.

[0128] To do this, the control module 210 can be connected directly or indirectly to said valves. Alternatively, said data, or said signals, can be collected by another module and transmitted to the control module 210.

[0129] [Fig.3] is a schematic representation of an exemplary embodiment not limiting of a hydrogen production unit according to the invention.

[0130] Unit 300 of [Fig.3] comprises all the elements of unit 200 of [Fig.2].

[0131] In addition, the unit 300 comprises a source 302 of neutral gas NG connected directly to the neutral gas inlet NG 212 on the air circuit 110.

[0132] Preferably, the neutral gas source 302 is a neutral gas reservoir.

[0133] Preferably, the neutral gas source 302 provides a neutral gas at a pressure su greater than or equal to the desired neutral gas pressure at the neutral gas inlet 202 of the air circuit 110.

[0134] For example, the neutral gas source 302 may comprise one or more pressurized neutral gas cylinders.

[0135] The unit 300 further comprises a source 304 of safety gas SG connected directly to the safety gas inlet SG 206 on the fuel circuit 120.

[0136] Preferably, the safety gas source 304 is a safety gas tank.

[0137] Preferably, the safety gas source 304 provides safety gas to a pressure greater than or equal to the desired safety gas pressure at the safety gas inlet 206 of the fuel circuit 120.

[0138] For example, the safety gas source 304 may comprise one or more pressurized safety gas cylinders.

[0139] [Fig.4] is a schematic representation of an exemplary embodiment not limiting of a method according to the invention.

[0140] The method 400 of [Fig.4] can be used to control a hydrogen production unit according to the invention and in particular the units 200 and 300 of FIGURES 2 and 3.

[0141] The method 400 comprises a shutdown phase 402 allowing a hydrogen production unit according to the invention to switch from a hydrogen production configuration to a hydrogen production shutdown configuration, while ensuring the integrity of the electrolysis cells.

[0142] The stop phase 402 comprises a step 404 of triggering the stop phase, comprising the following steps: - the opening of the neutral gas and safety gas inlets and outlets, and - closing other air and fuel circuit inlets and outlets. Preferably, these steps are performed, or at least triggered, simultaneously.

[0143] The shutdown phase 402 further comprises a purging step 406, during which: - the neutral gas and safety gas inlets and outlets are kept open, and - the other inlets and outlets of the air and fuel circuits are kept closed; for a predetermined period, for example 30 minutes. During this period the stack is purged, so as to eliminate traces of water as best as possible in the cells which can be assimilated to porous media.

[0144] Then, the stopping phase 402 comprises a cooling step 408 during which: - the neutral gas inlet and the safety gas inlet are kept open, - the neutral gas outlet and the safety gas outlet are closed, and - the other inlets and outlets of the air and fuel circuits are kept closed; until the stack temperature is less than or equal to a threshold temperature, for example 200°C.

[0145] Optionally, the method 400 may comprise a step 410 of detecting an incident on the air circuit or on the fuel circuit, for example depending on the state of a valve equipping said circuit and capable of affecting the pressure in said circuit.

[0146] This step 410 is carried out before the stopping phase 402.

[0147] When an incident is detected during step 410, the shutdown phase 402 is triggered automatically to carry out an emergency shutdown of the hydrogen production unit according to the invention.

[0148] Of course, the invention is not limited to the examples which have just been described.

Claims

Claims

1. Unit (200; 300) for producing hydrogen by high-temperature electrolysis of water vapor, said unit (200; 300) comprising: - a stack (102) of solid oxide cells, - a circuit (110), called the air circuit, passing through said stack (102), and comprising an air inlet (112) and an oxygen-enriched air outlet (114), in a hydrogen production configuration of said unit (200; 300), and - a circuit (120), called the fuel circuit, passing through said stack (102), comprising a water vapor inlet (122) and a hydrogen-enriched water vapor outlet (124), in said production configuration; characterized in that said unit (200; 300) is equipped with a system for stopping said unit (200;300), said shutdown system comprising: - an inlet (202) and an outlet (204) of neutral gas, provided on the air circuit (110) on either side of said stack (102), for circulating a predetermined neutral gas in said stack (102), in a shutdown configuration of said unit (200; 300), - an inlet (206) and an outlet (208) of safety gas, provided on the fuel circuit (120) on either side of said stack (102), for circulating a predetermined safety gas in said stack (102), in said shutdown configuration, and - a control module (210) for switching said stack (102) from the production configuration to the shutdown configuration.;

2. Unit (200; 300) according to the preceding claim, characterized in that the inlet (202) of neutral gas comprises: - at least one valve (214i) for regulating the passage of neutral gas, - optionally, a pressure regulator (212i) for regulating the pressure of the neutral gas in the air circuit (110).

3. Unit (200; 300) according to any one of the preceding claims, characterized in that the neutral gas outlet (204) comprises at least one valve (2142) for regulating the passage of neutral gas.

4. Unit (300) according to any one of the preceding claims, characterized in that the shutdown system further comprises a source (302) of neutral gas connected to the inlet (202) of neutral gas.

5. Unit (200; 300) according to any one of the preceding claims, characterized in that the safety gas inlet (206) comprises: - at least one regulating valve (2143) for the passage of safety gas, - optionally, a pressure regulator (2122) for regulating the pressure of the safety gas in the fuel circuit (120).

6. Unit (200; 300) according to any one of the preceding claims, characterized in that the safety gas outlet (208) comprises at least one safety gas passage regulating valve (2144).

7. Unit (300) according to any one of the preceding claims, characterized in that the shutdown system further comprises a source (304) of safety gas connected to the safety gas inlet (206).

8. Unit (200;300) according to any one of the preceding claims, characterized in that: - the neutral gas is, or comprises, nitrogen; and / or - the safety gas is, or comprises, an N2 / H2 mixture with a proportion of H2 less than or equal to 5%.

9. Unit (200; 300) according to any one of the preceding claims, characterized in that the control module (210) is configured to detect an incident on the air circuit (110) and / or an incident on the fuel circuit (120), and trigger the shutdown configuration.

10. Unit (200; 300) according to any one of the preceding claims, characterized in that the control module (210) is configured to carry out a shutdown phase (402) in order to switch said unit (200; 300) from the production configuration to the shutdown configuration, said shutdown phase (402) comprising a triggering step (404) comprising the following steps carried out in parallel: - opening of the neutral gas inlet (202) and of the outlet (204)

11.

12.

13. of neutral gas on the air circuit (110), and of the safety gas inlet (206) and the safety gas outlet (208) on the fuel circuit (120), and - closing of the other inlets and outlets of the air (110) and fuel (120) circuits. Unit (200; 300) according to any one of the preceding claims, characterized in that the control module (210) is configured to carry out, during the shutdown phase (402), a step (406) of purging said unit (200; 300) comprising the following steps: - keeping open the neutral gas inlet (202) and the neutral gas outlet (204) on the air circuit (110), and the safety gas inlet (206) and the safety gas outlet (208) on the fuel circuit (120), and - keeping the other inlets and outlets of the air (110) and fuel (120) circuits closed; for a predetermined duration, and / or until a predetermined pressure is reached in the stack (102) of cells. Unit (200; 300) according to any one of the preceding claims, characterized in that the control module (230) is configured to carry out, during the shutdown phase (402), a step (408) of cooling said unit (200; 300) comprising the following steps: - keeping open the neutral gas inlet (202) on the air circuit (110) and the safety gas inlet (206) on the fuel circuit (120), - closing the neutral gas outlet (204) on the air circuit (110) and the safety gas outlet (208) on the fuel circuit (120), and - keeping the other inlets and outlets of the air (110) and fuel (120) circuits closed; for a predetermined duration, and / or until reaching a temperature of the stack (102) below a predetermined threshold. Method (400) for controlling a hydrogen production unit (200; 300) according to any one of the preceding claims, said method (400) comprising a stopping phase (402) for switching said unit (200;300) from the production configuration to the stopping configuration, said phase (402) comprising a triggering step (404) comprising the following steps carried out in parallel: - opening the neutral gas inlet (202) and the neutral gas outlet (204) on the air circuit (110), and the safety gas inlet (206) and the safety gas outlet (208) on the fuel circuit (120), and - closing of the other inlets and outlets of the air (110) and fuel (120) circuits.

14. Method (400) according to the preceding claim, characterized in that the stopping phase (402) comprises a purging step (406) comprising the following steps: - keeping open the neutral gas inlet (202) and the neutral gas outlet (204) on the air circuit (110), and the safety gas inlet (206) and the safety gas outlet (208) on the fuel circuit (120), and - keeping the other inlets and outlets of the air (110) and fuel (120) circuits closed; for a predetermined duration, and / or until a predetermined pressure is reached in the stack (102).

15. Method (400) according to any one of claims 13 or 14, characterized in that the stopping phase (402) comprises a cooling step (408) comprising the following steps: - keeping open the neutral gas inlet (202) on the air circuit (110) and the safety gas inlet (206) on the fuel circuit (120), - closing the neutral gas outlet (204) on the air circuit (110) and the safety gas outlet (208) on the fuel circuit (120), and - keeping other inlets and outlets of the air (110) and fuel (120) circuits closed; for a predetermined duration, and / or until reaching a tem temperature of the stack (102) below a predetermined threshold.

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