Electrolysis system comprising a rebalancing line for a fluid provided with a degassing tank

Abstract

The invention relates to an electrolysis system (1) for producing a first mixture of a first gas and a fluid and a second mixture of a second gas and the fluid, a first separator (5) configured to separate the first mixture into a first sub-mixture comprising the first gas and condensates of the fluid and a second sub-mixture comprising fluid in which the first gas is dissolved and a second separator (9) configured to separate the second gas from the second mixture, the system comprising a production line (17) for the first gas configured to convey the first gas of the first sub-mixture from the first separator (5) to an outlet point (19), a third separator (23) being arranged on the production line (17) between the first separator (5) and the outlet point (19), the electrolysis system (1) comprising: a rebalancing line (39) for the fluid of the second sub-mixture extending between the first and second separators, comprising a degassing tank (41) connected to a vent (57), a transfer line (61) fluidically connecting the third separator (23) to the degassing tank (41).

Description

[0001] DESCRIPTION

[0002] Title of the invention: ELECTROLYSIS SYSTEM COMPRISING A FLUID REBALANCING LINE EQUIPPED WITH A DEGASING TANK.

[0003] The present invention relates to the field of water electrolysis, and more particularly to the balancing of flows circulating within an electrolysis system.

[0004] An electrolysis system typically uses one or more stacks of electrolyzers to perform electrolysis. This electrolysis process produces two mixtures: a first mixture composed of a gas and a fluid, and a second mixture composed of a second gas and a fluid. In the case of an electrolysis system performing water electrolysis, the first mixture produced consists of hydrogen and water, and the second mixture consists of oxygen and water.

[0005] To obtain these gases in their pure form, hydrogen and oxygen must be separated from the water contained in their respective mixtures. This separation is generally carried out in tanks called separators, where the gas and water separate by gravity: the water collects at the bottom of the separator, while the gas rises to the top. It should be noted, however, that after this separation, particularly in the case of hydrogen, it is saturated with residual water vapor. At the separator outlet, a first submixture is obtained, comprising hydrogen and water condensate, and a second submixture is obtained, consisting of water and hydrogen dissolved in water.

[0006] The hydrogen from the first submixture is then dried to remove this residual water, and this water is then generally removed from the electrolysis system. To perform this water electrolysis, electrolyzer stacks can include one or more electrolytic cells with an anodic compartment, where oxygen is formed, and a cathodic compartment, where hydrogen is formed, these two compartments being separated by a permeable membrane. During water electrolysis, when the first gas is hydrogen and the second gas is oxygen, an electro-osmotic flux phenomenon leads to an imbalance in the distribution of water within the compartments.Indeed, when passing through the permeable membrane, the protons carry water molecules with them, which causes an excess of water in the cathode compartment, resulting in a greater accumulation of water in the hydrogen-water separator than in the oxygen-water separator.

[0007] To avoid overflow of the hydrogen separator and loss of water, prior state-of-the-art electrolysis systems implement a balancing flow between the hydrogen separator and the oxygen separator, in order to counteract the electro-osmotic flow phenomenon.

[0008] However, during this water transfer, dissolved hydrogen remaining in the water of the hydrogen-water separator (corresponding to the second submixture identified above) can also be transported with the water to the oxygen-water separator. This increases the hydrogen concentration in the oxygen-water separator, and when this concentration reaches 4% in the oxygen, the gas mixture in the oxygen separator becomes potentially explosive. This explosion risk is amplified when the system is operating at low power, as the electrolyzer stack produces less oxygen, thus reducing the dilution of hydrogen in the oxygen-water separator.

[0009] Prior state-of-the-art systems, by counterbalancing the electro-osmotic flow phenomenon, therefore create a risk of explosion due to the interaction between hydrogen and oxygen in the oxygen-water separator caused by hydrogen transfer via the balancing flow. Furthermore, these prior state-of-the-art systems lose a significant amount of water by removing residual water contained in the separated hydrogen gas within the hydrogen-water separator.

[0010] The objective of the invention described in this document is therefore to overcome the disadvantages of the prior art by proposing a water electrolysis system comprising a rebalancing line that establishes a fluid balancing flow between a first separator and a second separator. This rebalancing line includes a degassing tank, which removes residual gas contained in the fluid to prevent any risk of explosion during the transfer of the fluid to the second separator. Furthermore, this electrolysis system includes a third separator that recovers the residual fluid contained in the gas separated in the first separator. This third separator is connected to the degassing tank, thus allowing this fluid to be recycled to help counteract the electroosmotic flow phenomenon.

[0011] The main object of the present invention is an electrolysis system comprising an electrolyzer stack configured to produce a first mixture of a first gas and a fluid and a second mixture of a second gas and the fluid, a first separator configured to separate the first mixture into a first submixture comprising the first gas and condensates of the fluid and a second submixture comprising fluid in which the first gas is dissolved, and a second separator configured to separate the second gas from the second mixture. The electrolysis system comprises a production line for the first gas configured to convey the first gas from the first submixture of the first separator to an outlet point of the electrolysis system, a third separator being disposed on the production line between the first separator and the outlet point, characterized in that the electrolysis system comprises:

[0012] - a rebalancing line for the fluid of the second submixture extending between the first separator and the second separator, said rebalancing line comprising a degassing tank connected to a vent by a degassing line,

[0013] - a transfer line fluidly connecting the third separator to the degassing tank.

[0014] The electrolysis system may include one or more stacks of electrolyzers. These stacks may be designed to perform water electrolysis. Typically, these stacks are composed of one or more electrolysis cells, each of which may be a proton exchange membrane electrolysis cell, consisting of an anodic part, a cathodic part, and a proton exchange membrane.

[0015] It is important to note that when the stacks perform water electrolysis, the first gas produced is hydrogen, and the fluid is water. The first mixture produced is therefore a hydrogen-water mixture. The second gas produced in this case is oxygen, and the fluid is also water. The second mixture is therefore an oxygen-water mixture. Thus, the first submixture comprises hydrogen and water condensates, and the second submixture comprises water in which hydrogen is dissolved.

[0016] The first mixture is then conveyed from the electrolyzer stack(s) to the first separator, and the second mixture is conveyed from the electrolyzer stack(s) to the second separator.

[0017] The first and second separators can be gravity separators, using gravity to separate, at least partially, the first and second gases from the fluid, respectively. It follows that the fluid (in which gas may be dissolved) collects at the bottom of both the first and second separators, while the first and second gases (which may contain fluid condensates) collect at the top of the first and second separators, respectively. In the case of water electrolysis, hydrogen (with water condensates) collects at the top of the first separator, while water (with hydrogen dissolved in the water) collects at its bottom. Similarly, oxygen collects at the top of the second separator, and water collects at its bottom.

[0018] The first submixture, accumulating in the headspace of the first separator, is then drawn off by the first gas production line and conveyed to the electrolysis system outlet. At this stage, the first submixture is saturated with gaseous fluid, which is why the production line may include a heat exchanger located between the first and third separators. This heat exchanger condenses the fluid saturating the first submixture. The third separator then separates the fluid condensate from the first gas. The first gas is then conveyed from the third separator to the electrolysis system outlet.

[0019] It is therefore understood that the first separator is upstream of the heat exchanger, the heat exchanger upstream of the third separator, and the third separator upstream of the electrolysis system's outlet point. As mentioned previously, an electro-osmotic flow phenomenon causes uneven fluid distribution in the separators. In fact, the fluid accumulates more in the first separator than in the second, resulting in an excess of fluid in the first separator and a deficiency in the second.

[0020] The rebalancing line of the electrolysis system fluidly connects the first separator to the second separator in order to convey the excess fluid from the first separator to the second separator, thus compensating for this electro-osmotic flow phenomenon.

[0021] It should be noted, however, that, as mentioned previously, the fluid separated in the first separator may contain residual traces of the first gas. If this fluid is conveyed directly to the second separator without treatment, this can lead to an interaction between the first and second gases, for example, an explosive situation if the first gas is hydrogen and the second gas is oxygen. To avoid this dangerous situation, the invention uses a rebalancing line comprising a degassing tank, located between the first and second separators.

[0022] The deaerating tank is designed to separate the fluid from the first residual gas it contains. The first residual gas is then vented from the deaerating tank via a deaerating line to the vent, where it is released from the electrolysis system. The fluid, now free of the first residual gas, is then routed from the deaerating tank to the second separator, thus preventing any dangerous interaction between the first and second gases in the second separator.

[0023] The deaerating tank therefore includes a fluid inlet from the first separator, but it also has another inlet for fluid from the third separator via the transfer line. Indeed, since the first gas is saturated with fluid after its separation in the first separator, a relatively large quantity of fluid can be recovered by the third separator. As a non-limiting example, in the case of water electrolysis, when hydrogen is 100% saturated with water, this corresponds to 0.07 kg of water per kg of hydrogen produced.

[0024] This fluid condensate may, however, contain residual first gas, which is why the transfer line connects the third separator to the deaerating tank. The fluid condensate is thus conveyed from the third separator to the deaerating tank, where it mixes with the fluid from the first separator. The residual first gas is then separated, and the fluid and condensate mixture, now free of first gas, is conveyed from the deaerating tank to the second separator, preventing any dangerous interaction between the first and second gases in the second separator.

[0025] The transfer line thus makes it possible to recycle fluid to counter the electro-osmotic flow phenomenon, thereby saving fluid while limiting the risks of interaction between gases thanks to the use of the degassing tank.

[0026] It should be noted that the first separator can be pressurized to a higher pressure than the second separator. In this way, the fluid is transferred from the first separator to the second separator due to the pressure differential. The deaerating tank can be pressurized to a pressure intermediate between that of the first and second separators. Thus, the fluid is transferred from the first separator to the deaerating tank, and then from the deaerating tank to the second separator, again using the pressure differential. Furthermore, this intermediate pressure in the deaerating tank facilitates the separation of the residual gas from the fluid in the first separator and the fluid condensate from the third separator.

[0027] The third separator can be pressurized to a higher pressure than the degassing tank, thus allowing the fluid condensate to be conveyed to the degassing tank thanks to the pressure differential.

[0028] By way of non-limiting examples, the first separator can be pressurized to a pressure between 22 and 32 bar, the second separator to a pressure between 3 and 11 bar, the third separator between 21 and 31 bar, and the degassing tank to a pressure between 5 and 13 bar.

[0029] According to an optional feature of the invention, the transfer line includes a modulating valve configured to control the flow rate of the fluid circulating in said transfer line.

[0030] The modulating valve can in particular be an on / off valve or a modulating valve, that is to say that it can only be in the fully open position or in the fully closed position in the case of an on / off valve, or it can be in the fully open position, in the fully closed position or in a plurality of intermediate positions between the fully open position and the fully closed position when it is a modulating valve.

[0031] Thus, in the case of an on / off valve, the modulating valve controls whether or not the fluid condensate is routed from the third separator to the deaerating tank, and in the case of a modulating valve, the modulating valve also controls the amount of fluid condensate routed from the third separator to the deaerating tank.

[0032] The modulating valve can also be configured to expand the fluid condensate, reducing it from the pressure at which the third separator is pressurized to the pressure at which the deaerating tank is pressurized.

[0033] Alternatively, this pressure reduction can be achieved by a pressure reduction device independent of the modulating valve, located on the transfer line. Optionally, the transfer line may include a transfer orifice positioned downstream of the modulating valve and configured to control the flow rate and / or pressure of the fluid circulating in said transfer line.

[0034] According to an optional feature of the invention, the third separator includes a sensing device configured to detect a separation surface between the first gas and the fluid within the third separator. This separation surface corresponds to the gas / liquid interface in the third separator. By sensing this separation surface, the sensing device can therefore monitor the quantity of fluid and first gas contained within the third separator.

[0035] The detection device can thus be configured to determine when the separation surface between the first gas and the fluid has reached too high a level in the third separator, thus signaling an excessive amount of fluid in this third separator.

[0036] According to an optional feature of the invention, the degassing line includes a regulating valve configured to control the flow rate of the first gas circulating within said degassing line.

[0037] The control valve thus allows the quantity of first gas evacuated from the electrolysis system by the vent via the degassing line to be regulated, and therefore, indirectly, the quantity of first gas present in the degassing tank.

[0038] According to an optional feature of the invention, the degassing tank includes a sensor configured to detect a boundary between the first gas and the fluid within the degassing tank.

[0039] The boundary between the first gas and the fluid within the deaerating tank corresponds to the gas / liquid interface. By detecting this boundary, the sensor can assess the amount of fluid and the amount of first gas contained in the deaerating tank. For example, if the first gas / fluid boundary is too low, this indicates an excessive amount of first gas in the deaerating tank. Conversely, if the first gas / fluid boundary is too high, this indicates an excessive amount of fluid. The sensor can therefore be configured to detect when the first gas / fluid boundary is too low and / or too high.

[0040] Optionally, the deaerating tank can also include a detector configured to detect this boundary between the first gas and the fluid. In this case, the sensor could be configured to detect a boundary between the first gas and the fluid that reaches a level that is too low, while the detector could be used to detect a boundary between the first gas and the fluid that reaches a level that is too high.

[0041] According to an optional feature of the invention, the rebalancing line comprises a first part fluidly connecting the first separator to the deaerating tank and a second part fluidly connecting the deaerating tank to the second separator, the first part of the rebalancing line comprising a first control valve configured to regulate the pressure of the fluid circulating in said first part and the second part of the rebalancing line comprising a second control valve configured to regulate the flow rate of the fluid circulating in said second part.

[0042] In other words, the first part of the rebalancing line is configured to carry the second submix from the first separator to the degasser tank, and the second part is configured to carry the fluid from the degasser tank to the second separator.

[0043] It should be noted that the first and second control valves can be either on / off or variable valves. The first control valve, located on the first part of the rebalancing line, regulates the pressure of the second submix between the first separator and the deaerating tank. The second control valve, located on the second part of the rebalancing line, regulates the flow of fluid from the deaerating tank to the second separator. It should also be noted that the first control valve can be configured to reduce the fluid flowing through it, lowering the pressure from the first separator to the pressure of the deaerating tank.

[0044] Optionally, the first control valve can also be configured to regulate the flow of fluid circulating in the first part of the rebalancing line.

[0045] Similarly, the second control valve can relieve the fluid flowing through it, reducing the fluid pressure from the degasser tank to the pressure of the second separator.

[0046] Alternatively, the first and second parts of the rebalancing line may each include an expansion device independent of the first control valve and the second control valve and allowing the expansion of the fluid.

[0047] According to an optional feature of the invention, the first separator includes a detection means configured to detect an interface between the first submixture and the second submixture within the first separator.

[0048] By detecting this interface, the detection means can therefore determine the quantity of second submixture (mostly fluid) and first submixture (mostly first gas) contained in the first separator.

[0049] It should be noted that when the interface between the first and second submixtures reaches an excessively high level, this corresponds to an excessive amount of fluid in the first separator, indicating that the electro-osmotic flow phenomenon has increased the amount of fluid in the first separator. This increase, in turn, reduces the amount of fluid in the second separator. The detection method can therefore be configured, in particular, to detect when the interface between the first and second submixtures reaches an excessively high level, in order to monitor the electro-osmotic flow phenomenon.

[0050] According to an optional feature of the invention, the electrolysis system includes a piloting element for the valve(s), the piloting element being configured to control the second control valve of the second part of the rebalancing line as a function of the interface between the first gas and the fluid within the first separator.

[0051] The control unit allows, in particular, the control of at least one of the following: the first control valve, the second control valve, the regulating valve, and the modulating valve. The control of the second control valve is based on the interface between the first gas and the fluid detected in the first separator. In other words, the control of the second control valve is based on the detection of this interface by the detection system of the first separator.

[0052] For example, when the interface between the first gas and the fluid reaches an excessively high level in the first separator, it means that the electro-osmotic flow phenomenon has introduced too much fluid into the first separator. It then becomes necessary to rebalance the fluid between the first and second separators. The control unit, upon receiving information from the detection system indicating that the interface has reached an excessively high level, triggers the opening of the second control valve to allow the fluid contained in the deaerating tank to be routed to the second separator.

[0053] Optionally, the control unit can also open the first valve upon receiving this information, so that the fluid contained in the first separator is routed to the degasser tank.

[0054] According to an optional feature of the invention, the control element is configured to control the degassing line regulating valve based on the boundary between the first gas and the fluid within the degassing tank. The degassing line regulating valve is therefore controlled according to the boundary between the first gas and the fluid within the degassing tank, as detected by the sensor.

[0055] More specifically, when the boundary between the first gas and the fluid in the deaerator tank reaches a predetermined low level, it means that an excessive amount of first gas is present in the deaerator tank. The sensor then sends a signal to the control unit, which in turn opens the regulating valve to release the excess first gas from the deaerator tank.

[0056] According to an optional feature of the invention, the pilot member is configured to control the modulation valve of the transfer line as a function of the separation surface between the first gas and the fluid within the third separator.

[0057] The modulating valve is therefore controlled based on the separation area detected by the third separator's detection device. Specifically, when the separation area between the first gas and the fluid within the third separator reaches a predetermined, excessive level, it indicates that an excessive amount of fluid is present in the third separator. The detection device then sends an alert to the control unit, which can then open the modulating valve to release the excess fluid and direct it to the deaerating tank.

[0058] The invention also relates to a method of controlling the electrolysis system as described in this application, in which the pilot member controls the second control valve when the interface between the first gas and the fluid within the first separator reaches a predefined maximum level.

[0059] This maximum level is reached when the interface between the first gas and the fluid in the first separator becomes too high, thus necessitating the refilling of the second separator with fluid. In this case, the detection device sends a signal to the control unit, which in turn sends a signal to the second control valve to open it. This allows the fluid from the deaerating tank to be discharged into the second separator, thereby balancing the amount of fluid between the first and second separators.

[0060] Optionally, the process can also allow the first control valve to be opened when the interface between the first submixture and the second submixture within the first separator reaches the predefined maximum level, so that the second submixture contained in the first separator is discharged into the degasser tank at the same time as the fluid from the degasser tank is discharged into the second separator and that this second submixture is decompressed.

[0061] It should be noted that this fluid transfer occurs thanks to the pressure differential between the first separator and the degasser tank, as well as the pressure differential between the degasser tank and the second separator. The invention also relates to a method for controlling the electrolysis system as described in this application, in which the pilot element controls the regulating valve when the boundary between the first gas and the fluid within the separator tank reaches a predefined minimum threshold.

[0062] This minimum threshold corresponds to a level where the boundary between the first gas and the fluid in the degassing tank becomes too low, indicating that it is necessary to vent the first gas because its quantity in the degassing tank is excessive. To do this, the sensor sends a signal to the control unit, which then signals the regulating valve to open it and vent the excess first gas from the degassing tank through the electrolysis system vent via the degassing line.

[0063] The invention also relates to a method for controlling the electrolysis system as described in this application, in which the control element controls the modulating valve when the separation surface between the first gas and the fluid within the third separator reaches a maximum limit. This maximum limit is reached when the separation surface between the first gas and the fluid in the third separator becomes too high, necessitating the discharge of the fluid from the third separator to the degasser tank. The detection means then sends an alert to the control element, which signals the modulating valve to open it, thus allowing the fluid from the third separator to be discharged into the degasser tank.

[0064] It should be noted that this fluid transfer is achieved through the pressure differential between the third separator and the degassing tank.

[0065] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and an example of an embodiment given by way of illustration and not limitation with reference to the attached drawing on the other hand, in which:

[0066] [Fig. i] is a schematic diagram of an electrolysis system according to one embodiment of the invention.

[0067] [Fig. 2] is a schematic representation of a first mode of operation of the electrolysis system of the embodiment of figure 1.

[0068] [Fig. 3] is a schematic representation of a second operating mode of the electrolysis system of the embodiment shown in the figure. The features and variants of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of the features described below, isolated from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0069] Figure 1 is a schematic diagram of an electrolysis system 1 according to one embodiment of the invention. The electrolysis system 1 comprises at least one electrolyzer stack 3 configured to perform electrolysis, for example, the electrolysis of water. The electrolyzer stack 3 produces, on the one hand, a first mixture composed of a first gas and a fluid, and on the other hand, a second mixture composed of a second gas and said fluid.

[0070] In the case where the electrolyzer stack 3 performs water electrolysis, the first gas is hydrogen, the second gas is oxygen, and the fluid is water. The first mixture is thus primarily composed of hydrogen and water, while the second mixture is primarily composed of oxygen and water. For this purpose, the electrolyzer stack 3 can, in particular, be a membrane electrolyzer stack, composed of one or more electrolytic cells, each comprising a cathode compartment, an anodic compartment, and an electrolytic membrane.

[0071] The electrolyzer stack 3 is fluidly connected to a first separator 5 of the electrolysis system 1 via a first line 7, and to a second separator 9 of the electrolysis system 1 via a second line 11. This first line 7 is configured to carry the first mixture from the electrolyzer stack 3 to the first separator 5, while the second line 11 is configured to carry the second mixture from the electrolyzer stack 3 to the second separator 9.

[0072] The first separator 5 is configured to separate the first mixture into a first submixture comprising the first gas and condensates from the fluid, and a second submixture comprising fluid in which the first gas is dissolved. In the case of water electrolysis, the hydrogen-water mixture downstream of the electrolyzer stack is separated into hydrogen with water condensates (first submixture) and water with dissolved hydrogen (second submixture). For this purpose, the first separator 5 can utilize gravity, so that the first submixture remains predominantly in an upper portion 13 of the first separator 5, while the second submixture remains mainly in a lower portion 15 of the first separator 5.

[0073] The electrolysis system 1 includes a first gas production line 17 connecting the first separator 5 to an outlet point 19 of the electrolysis system 1. More particularly, this first gas production line 17 fluidly connects the upper part 13 of the first separator 5 to the outlet point 19, so that the first gas production line 17 allows the first gas from the first submixture separated from the first separator 5 to the outlet point 19.

[0074] As explained previously, the presence of a heat exchanger on the production line is not mandatory. In the following, we will assume that production line 17 includes this heat exchanger. However, a person skilled in the art will understand from the description that the principle of the invention can be applied similarly without a heat exchanger on the production line.

[0075] The production line 17 of the first gas includes in particular a heat exchanger 21 and a third separator 23, arranged successively on this production line 17 between the first separator 5 and the outlet point 19. In other words, the third separator 23 is located between the first separator 5 and the outlet point 19 of the production line 17 of the first gas, and the heat exchanger 21 is placed on this same production line 17 between the first separator 5 and the third separator 23.

[0076] It follows that, in a direction of circulation of the first gas going from the first separator 5 to the outlet point 19 of the electrolysis system 1, the heat exchanger 21 is disposed downstream of the first separator 5, the third separator 23 is located downstream of the heat exchanger 21, and the outlet point 19 is located downstream of the third separator 23.

[0077] When the first submixture is drawn off by production line 17 at the upper part 13 of the first separator 5, it may be saturated with fluid in gaseous form. In the case of water electrolysis by electrolysis system 1, the hydrogen drawn off by production line 17 at the upper part 13 of the first separator 5 may thus be saturated with water vapor.

[0078] The heat exchanger 21, located downstream of the first separator 5, has the role of condensing the gaseous fluid that saturates the first gas. To achieve this, the heat exchanger 21 can be configured to cool the first gas exiting the first separator 5, thereby condensing the fluid that saturates it and forming a fluid condensate.

[0079] Positioned downstream of the heat exchanger 21, the third separator 23 is configured to separate this fluid condensate from the first gas. As a non-limiting example, the separation can be carried out by gravity within the third separator 23, with the first gas accumulating in an upper zone 25 of the third separator 23, while the fluid condensate accumulates in a lower zone 27 of the third separator 23. The production line 17 then draws the first gas separated from the fluid condensate to convey it to the outlet 19. For this purpose, the first gas production line 17 draws this first gas from the upper zone 25 of the third separator 23.

[0080] In other words, a first portion 29 of the production line 17 is fluidly connected to the upper part 13 of the first separator 5 to collect the first gas saturated with fluid. This first portion 29 passes through the heat exchanger 21, where the fluid saturating the first gas is condensed. This first portion 29 of the production line 17 is also fluidly connected to the third separator 23, so as to discharge the first gas and the fluid condensate. In this third separator 23, the first gas and the fluid condensate are separated. A second portion 31 of the production line 17 is fluidly connected to the upper area 25 of the third separator 23 in order to convey the first gas, separated from the fluid condensate, to the outlet 19 of the electrolysis system 1. It should be noted that after the outlet 19 of the electrolysis system 1, the first gas can undergo further processing necessary for its production.By way of non-limiting example, it can be treated by treatment means, stored by storage means, or consumed by means of consuming the first gas.

[0081] The second separator 9 is configured to separate the second gas from the mixture; that is, in the case of water electrolysis, to separate the oxygen from the oxygen-water mixture. The second separator 9 can also use gravity so that the second gas remains mainly in an upper portion 33 of the separator, while the fluid remains mainly in a lower portion 35.

[0082] The electrolysis system 1 includes a second gas production line 37, connecting the second separator 9 to a discharge point 38 of the electrolysis system 1. More specifically, this production line 37 is fluidly connected to the upper portion 33 of the second separator 9. The second gas production line 37 thus allows the second separated gas, i.e. oxygen in the case of water electrolysis, to be conveyed to the discharge point 38 of the electrolysis system 1.

[0083] It should be noted that after the discharge point 38 of the electrolysis system 1, the second gas may undergo further processing necessary for its production. By way of non-limiting example, it may be treated by processing means, stored by storage means, or consumed by means used for consuming the first gas.

[0084] The electrolysis system 1 includes a rebalancing line 39 configured to allow fluid exchange between the first separator 5 and the second separator 9. To this end, the rebalancing line 39 fluidly connects the first separator 5 to the second separator 9. More precisely, the rebalancing line 39 is fluidly connected to the lower part 15 of the first separator 5 and to the second separator 9, so as to draw the fluid accumulating in the lower part 15 of the first separator 5 and convey it to the second separator 9. The rebalancing line 39 includes a deaerating tank 41, configured to extract the residual first gas still present in the second submixture circulating within this line. Indeed, despite the separation of the first gas from the first mixture within the first separator 5, a quantity of residual first gas remains in the second submixture from said first separator 5.

[0085] This degassing tank 41 is therefore positioned on the rebalancing line 39, between the first separator 5 and the second separator 9, to allow the extraction of this first residual gas from the fluid. To this end, the degassing tank 41 is configured so that the first gas accumulates in an upper section 47, while the fluid accumulates in a lower section 49 of said degassing tank 41. This allows, notably through a pressure change, the separation of the first residual gas from the fluid coming from the first separator 5.

[0086] More specifically, the rebalancing line 39 comprises a first part 43 connecting the first separator 5 to the degassing tank 41, and a second part 45 connecting the degassing tank 41 to the second separator 9. The first part 43 is fluidly connected to the first separator 5, in particular to its lower part 15. In this way, the first part 43 is configured to draw the fluid contained in the first separator 5 and convey it to the degassing tank 41.

[0087] The second part 45 of the rebalancing line 39 fluidly connects the lower section 49 of the degassing tank 41 to the second separator 9. As a result, the second part 45 of the rebalancing line 39 is configured to take the fluid from the degassing tank 41 and convey it to the second separator 9.

[0088] The first part 43 of the rebalancing line 39 includes a first control valve 51, while the second part 45 of the rebalancing line 39 includes a second control valve 53. The first control valve 51 is configured in particular to control the pressure of the second submixture circulating in the first part 43 of the rebalancing line 39, while the second control valve 53 is configured to control the flow rate of fluid circulating in the second part 45 of the rebalancing line 39.

[0089] The first control valve 51 and the second control valve 53 can be, in particular, on / off valves, that is, valves capable of assuming a fully open or fully closed position, without being able to assume an intermediate position between these two positions. They can also be variable valves, that is, capable of assuming a plurality of intermediate positions between the fully open and fully closed positions. As a result, when the first control valve 51 is in a fully open position, the second submixture circulating in the first part 43 of the rebalancing line 39 is relaxed.

[0090] Furthermore, the first control valve 51 can be configured to regulate the flow of the second submixture circulating in the first part 43 of the rebalancing line 39. In this case, when the first control valve 51 is in a fully closed position, the second submixture is prevented from flowing from the first separator 5 to the deaerating tank 41. Conversely, when the first valve is in a fully open position or in any intermediate position between the fully open and fully closed positions, the first part 43 of the rebalancing line 39 can draw from the second submixture in the lower part 15 of the first separator 5 and convey it to the deaerating tank 41.

[0091] When the second control valve 53 is in a fully closed position, fluid is prevented from flowing from the degasser tank 41 to the second separator 9. Conversely, when the second control valve 53 is in a fully open position or in any intermediate position between the fully open and fully closed positions, the second part 45 of the rebalancing line 39 can draw fluid from the lower section 49 of the degasser tank 41 and convey it to the second separator 9. The degasser tank 41 is also connected to a degassing line 55, which is fluidically connected to the upper section 47 of the degasser tank 41 to allow the first gas accumulating in this upper section 47 to be drawn off.

[0092] The degassing line 55 thus fluidly connects the upper section 47 of the degassing tank 41 to a vent 57 of the electrolysis system 1, this vent 57 being configured to vent the first gas from the electrolysis system 1. In other words, the degassing line 55 recovers the first gas contained in the upper section 47, that is to say the first gas separated from the fluid within the degassing tank 41, and conveys it to the vent 57 to vent it from the electrolysis system 1.

[0093] This degassing line 55 includes a control valve 59, configured to control the flow rate in this line, in this case, the flow rate of the first gas. This control valve 59 can also be an on / off valve or a variable valve.

[0094] This control valve 59 thus allows the degassing line 55 to draw or not the first gas from the upper section 47 of the degassing tank 41. More precisely, when the control valve 59 is in the fully closed position, the degassing line 55 cannot draw any first gas from the upper section 47 of the degassing tank 41 nor convey it to the vent 57. On the other hand, when the control valve 59 is in the fully open position or in any intermediate position between the fully open and fully closed positions, the degassing line 55 can draw some first gas from the upper section 47 of the degassing tank 41 and convey it to the vent 57 so that it can be vented from the electrolysis system 1.

[0095] The electrolysis system 1 also includes a fluid transfer line 61. This transfer line 61 is configured to recover the fluid condensate separated from the first gas within the third separator 23 and convey it to the degassing tank 41. To this end, the fluid transfer line 61 extends between the third separator 23 and the degassing tank 41. More specifically, this line is fluidically connected to the lower zone 27 of the third separator 23, thus allowing the collection of fluid condensate present in the third separator 23 and its conveyance to the degassing tank 41. Consequently, this fluid condensate is mixed with the fluid from the first separator 5, and this mixture is then degassed before being conveyed to the second separator 9.

[0096] The transfer line 61 includes a modulating valve 63, configured to control the flow rate within this line. This modulating valve 63 can also be an on / off valve or a modulating valve.

[0097] As a result, when the modulating valve 63 is in the fully closed position, fluid is prevented from being drawn from the lower section 49 of the third separator 23 and therefore prevented from being conveyed from the third separator 23 to the degassing tank 41. On the other hand, when the modulating valve 63 is in the fully open position or in any intermediate position between the fully open and fully closed positions, the fluid accumulating in the lower area 27 of the third separator 23 is drawn and conveyed to the degassing tank 41.

[0098] Optionally, the transfer line 61 may include a transfer port positioned downstream of the modulating valve 63 and configured to control the flow rate and / or pressure of the fluid flowing in said transfer line 61.

[0099] The electrolysis system 1 includes a control unit 65 designed to control the various valves of the electrolysis system 1. This control unit 65 can therefore, in particular, control at least one of the following: the first control valve 51, the second control valve 53, the modulating valve 63, and the regulating valve 59. To exert this control, the control unit 65 can, for example, be electrically connected to each of the valves. The electrolysis system 1 also includes sensing elements that provide the control unit 65 with information for controlling the valves. The first separator 5 is thus equipped with a sensing device 67 that determines the fluid level in the first separator 5 by being configured to detect an interface IN between the first submixture and the second submixture in the first separator 5.

[0100] More specifically, this detection means 67 signals to the control unit 65 when the interface IN between the first submixture and the second submixture reaches a maximum level MA by emitting a signal. In other words, it identifies when the quantity of the second submixture in the separator reaches the predefined maximum level MA and transmits this information to the control unit 65, which can then send one or more signals to control the valves accordingly.

[0101] The degassing tank 41 is equipped with a sensor 69 which determines the level of fluid that the degassing tank 41 contains by being configured to detect a limit LI between the first gas and the fluid in the degassing tank 41. It should be noted that this limit LI between the first gas and the fluid corresponds to a gas / liquid interface.

[0102] Sensor 69 is configured to alert control unit 65 when the boundary LI between the first gas and the fluid reaches a predefined minimum threshold MI, by sending a transmission. When this minimum threshold MI is reached, it indicates that a significant quantity of first gas is present in the degasser tank 41. Following this transmission, control unit 65 is configured to send appropriate signals to one or more valves for control. For example, it may order the opening of control valve 59 to allow the first gas to be vented from the degasser tank 41 to vent 57, via degassing line 55.

[0103] The third separator includes a detection device 70 configured to detect a separation surface SS between the first gas and the fluid within the third separator 23, this separation surface SS corresponding to the gas / liquid interface in the third separator. In this embodiment, the detection device 70 is designed to determine when the separation surface SS between the first gas and the fluid reaches an excessive level in the third separator 23, thus signaling an excessive amount of fluid in this separator by issuing an alert to the control unit 65. More specifically, the detection device 70 sends the alert when the separation surface SS exceeds a maximum limit LM. The control unit 65 can then command the opening of the modulating valve 63 to discharge the excess fluid from the third separator 23 and convey it to the deaerating tank 41.

[0104] Figure 2 is a schematic representation of a first mode of operation of the electrolysis system 1 of the embodiment of Figure 1.

[0105] It should also be noted that in figures 2 and 3, the direction of fluid flow is represented by arrows.

[0106] The electrolyzer stack 3 produces the second mixture, which flows through the second pipe 11 of the electrolyzer stack 3 to the second separator 9, where the second gas is at least partially separated from the second mixture. The second gas thus separated is then drawn off from the second separator 9 and conveyed to the discharge point 38 of the electrolysis system 1.

[0107] Simultaneously, the first mixture produced by the electrolyzer stack 3 is conveyed through the first pipe 7 to the first separator 5, where it is separated into a first submixture and a second submixture as previously explained. The first gas, at this point saturated with fluid in its gaseous form, is withdrawn from the first separator 5 by the production line 17 and then conveyed via said production line 17, passing through the heat exchanger 21, to the third separator 23. Within the heat exchanger 21, the fluid saturating the first gas is condensed, forming the fluid condensate, which is then separated from the first gas in the third separator 23. The first gas thus separated is then conveyed to the outlet 19 via the first gas production line 17.

[0108] In this first operating mode, the interface IN between the first gas and the fluid within the first separator 5 is at a level lower than the previously defined maximum level MA. In other words, the electro-osmotic flow phenomenon has not sufficiently raised the interface IN in the first separator 5 to trigger the balancing flow via the rebalancing line 39. The detection means 67 therefore sends no information to the control unit 65 to command the opening of the first control valve 51 or the second control valve 53. These two control valves 51 and 53 thus remain completely closed, preventing any fluid circulation in the rebalancing line 39.

[0109] Simultaneously, the separation surface SS between the first gas and the fluid condensate within the third separator 23 is below the previously defined maximum limit LM. Therefore, the detection device 70 does not send an alert to the control unit 65 to open the modulating valve 63. Consequently, this modulating valve 63 remains closed, preventing any fluid flow in the transfer line 61.

[0110] In the degassing tank 41, the boundary LI between the first gas and the fluid is below the minimum threshold ML. In other words, an excessive amount of first gas is present in the degassing tank 41. The sensor 69 detects this situation and sends a transmission T to the control unit 65, which in response sends an opening signal Si to the control valve 59. This triggers the opening of the control valve 59, allowing the first gas to be discharged from the degassing tank 41 via the degassing line 55.

[0111] Figure 3 is a schematic representation of a second operating mode of the electrolysis system 1 of the embodiment shown in Figure 1. In this second operating mode, the circulation within the first pipe 7, the second pipe 11, the second gas production line 37, and the first gas production line 17 is similar to that of the first operating mode. However, in this second operating mode, the interface IN between the first and second submixtures within the first separator 5 is at a level higher than the maximum level MA, indicating that the electro-osmotic flow phenomenon has led to an excessive increase in the fluid in the first separator 5. The sensing means 67 perceives this situation and sends a signal I to the control unit 65, which then controls the opening of the first control valve 51 and the second control valve 53 by means of signals S2 and S3.This actuation then allows the fluid to circulate from the first separator 5 to the degassing tank 41, and from the degassing tank 41 to the second separator 9, thanks to the rebalancing line 39.

[0112] It should be noted that, in other operating modes, the pilot unit 65 could open only one of the two control valves 51, 53, for example only the second control valve 53.

[0113] One embodiment proposes that the second control valve 53 be periodically placed in the open position to regulate the level of the first mixture in the first separator 5 so that the interface IN between the first gas and the fluid in the first separator 5 is at a level lower than the previously defined maximum level MA. In such a case, the second control valve 53 could, for example, be in the open position for 50% of its operating time. The second control valve 53 will be controlled via the control element 65, which will receive information from the detection means 67. This information will determine the fluid level in the first separator 5 by being configured to detect an interface IN between the first and second submixtures in the first separator 5.

[0114] Another embodiment proposes that the second control valve 53 be able to adapt its opening rate according to the flow rate of the fluid to be evacuated within the first separator 5, so that the interface IN between the first gas and the fluid within the first separator 5 is at a level lower than the maximum level MA defined previously. In such a case, the second control valve 53 will also be controlled via the control element 65, which will receive information from the detection means 67, allowing it to determine the fluid level in the first separator 5 by being configured to detect an interface IN between the first submixture and the second submixture in the first separator 5. Such an embodiment allows for optimized sizing of the first separator 5 and the rebalancing line 39.

[0115] It should also be noted that the fluid circulation between the first separator 5 and the second separator 9 is achieved through a pressure differential between these two separators 5 and 9. More precisely, the pressure in the second separator 9 is lower than that in the degasser tank 41, which is itself lower than the pressure in the first separator 5. Control valves 51 and 53 can, for example, facilitate this pressure reduction. In addition to enabling circulation, this pressure differential promotes the gasification of the residual first gas present in the fluid from the first separator 5. This facilitates the degassing of the first gas in the degasser tank 41 and prevents the fluid delivered to the second separator 9 from still containing any residual first gas.

[0116] In this second operating mode, the separation surface SS between the first gas and the fluid condensate within the third separator 23 exceeds the maximum limit LM. The detection device 70 then sends an alert A to the control unit, which reacts by opening the modulating valve 63 via a signal S4.

[0117] Once opened, the modulating valve 63 allows the fluid condensate to flow from the third separator 23 to the degasser tank 41, where it mixes with the fluid from the first separator 5. It should also be noted that the modulating valve 63 is capable of gas expansion, which keeps the pressure in the degasser tank 41 lower than that of the third separator 23. Thus, the fluid condensate flows from the third separator 23 to the degasser tank 41 thanks to the pressure differential, and the residual gas is gasified by this pressure drop, facilitating its degassing in the degasser tank 41.

[0118] The invention also relates to a method for controlling the electrolysis system. This method allows the control unit 65 to control the second control valve 53 and / or the first control valve 51 when the interface IN between the first gas and the fluid within the first separator 5 reaches the maximum level MA.

[0119] Furthermore, this control method allows the pilot unit 65 to control the regulating valve 59 when the boundary between the first gas and the fluid within the deaerating tank 41 reaches the minimum threshold MI. The control method of the electrolysis system 1 also allows the pilot unit 65 to control the modulating valve 63 when the separation surface SS between the first gas and the fluid within the third separator 23 reaches the maximum limit LM.

[0120] The present invention thus proposes an electrolysis system comprising a rebalancing line equipped with a degassing tank, connecting a first separator to a second separator, in order to counteract the electro-osmotic flow phenomenon while preventing any explosive situation. The electrolysis system also includes a transfer line that recycles a fluid contained in a first gas to help counteract the electro-osmotic flow phenomenon. The invention is based on a judicious arrangement of the degassing tank between the first and second separators and takes advantage of a pressure differential between these two separators to circulate the submixture of fluid with the first dissolved gas from the first separator to the second separator. Furthermore, by connecting the third separator to the degassing tank, the condensed fluid is recycled, thus preventing any overconsumption of fluid in the system.While retaining all of the fluid within the system, the invention ensures safe conditions by venting the first gas dissolved in the fluid before redirecting the fluid to the second separator. The degassing tank can be viewed as a dynamic filter that performs a final separation between the fluid and the first gas.

[0121] The present invention is not limited to the means and configurations described and illustrated herein, and also extends to any equivalent means and configuration as well as any technically operative combination of such means.

Claims

DEMANDS:

1. Electrolysis system (i) comprising an electrolyzer stack (3) configured to produce a first mixture of a first gas and a fluid and a second mixture of a second gas and the fluid, a first separator (5) configured to separate the first mixture into a first submixture comprising the first gas and condensates of the fluid and a second submixture comprising fluid in which the first gas is dissolved, and a second separator (9) configured to at least partially separate the second gas from the second mixture, the electrolysis system comprising a production line (17) for the first gas configured to convey the first gas from the first submixture of the first separator (5) to an outlet point (19) of the electrolysis system (1), a third separator (23) being disposed on the production line (17) between the first separator (5) and the outlet point (19), characterized in that the electrolysis system (1) comprises: - a rebalancing line (39) of the fluid of the second submixture extending between the first separator (5) and the second separator (9), said rebalancing line (39) comprising a degassing tank (41) connected to a vent (57) by a degassing line (55), - a transfer line (61) fluidically connecting the third separator (23) to the degassing tank (41).

2. An electrolysis system (1) according to claim 1, wherein the transfer line (61) comprises a modulating valve (63) configured to control the flow rate of the fluid circulating in said transfer line (61).

3. An electrolysis system (1) according to any one of claims 1 or 2, wherein the degassing line (55) comprises a regulating valve (59) configured to control the flow rate of the first gas circulating within said degassing line (55).

4. Electrolysis system (1) according to any one of claims 1 to 3, wherein the degassing tank (41) includes a sensor (69) configured to detect a boundary (LI) between the first gas and the fluid within the degassing tank (41). 5- Electrolysis system (i) according to any one of claims i to 4, wherein the rebalancing line (39) comprises a first part (43) fluidly connecting the first separator (5) to the degassing tank (41) and a second part (45) fluidly connecting the degassing tank (41) to the second separator (9), the first part (43) of the rebalancing line (39) comprising a first control valve (51) configured to regulate the pressure of the fluid circulating in said first part (43) and the second part (45) of the rebalancing line (39) comprising a second control valve (53) configured to regulate the flow rate of the fluid circulating in said second part (45) of the rebalancing line (39).

6. An electrolysis system (1) according to any one of claims 1 to 5, wherein the first separator (5) comprises a detection means (67) configured to detect an interface (IN) between the first submixture and the second submixture within the first separator (5).

7. An electrolysis system (1) according to any one of claims 1 to 6 in combination with claim 5, comprising a pilot member (65) for the valve(s) (51, 53, 59, 63), the pilot member (65) being configured to control the second control valve (53) of the second part (45) of the rebalancing line (39) as a function of the interface (IN) between the first submixture and the second submixture within the first separator (5).

8. Electrolysis system (1) according to claim 7 in combination with claim 4, wherein the pilot member (65) is configured to control the regulating valve (59) of the degassing line (55) as a function of the boundary (LI) between the first gas and the fluid within the degassing tank (41).

9. Method of controlling the electrolysis system (1) according to any one of claims 7 or 8, wherein the pilot member (65) controls the second control valve (53) when the interface (IN) between the first submixture and the second submixture within the first separator (5) reaches a predefined maximum level (MA). io. Method of controlling the electrolysis system (i) according to claim 8, wherein the pilot member (65) controls the regulating valve (59) when the limit (LI) between the first gas and the fluid within the degasser tank (41) reaches a predefined minimum threshold (MI).

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