Extending the operating range of an electrolysis system by optimizing the electrolyte flow rate

Abstract

The present invention relates to an electrolysis unit (10) comprising: - a pump (12), - an electrolysis module (14), - a first gas-liquid separator (20) dedicated to the separation of the hydrogen-lye mixture, and - a second gas-liquid separator (22) dedicated to the separation of the oxygen-lye mixture, the electrolysis unit (10) further comprising: - at least one gas analyzer capable of providing information on the residual level of oxygen in the first gas-liquid separator (20) or of hydrogen in the second gas-liquid separator (22), - a control unit configured to receive and process the residual level information and to provide a lye flow rate command as a function of the residual level information, - a means for adapting the lye flow rate configured to receive the lye flow rate command and to adapt the lye flow rate as a function of the lye flow rate command. Figure for the abstract: 1

Description

Title of the invention: Enlarging the operating range of an electrolysis system by optimizing the electrolyte flow rate Technical field of the invention

[0001] The present invention relates to a method for regulating the flow of electrolyte within an electrolysis unit and circulation loop. Technical background

[0002] An electrolysis unit conventionally comprises an electrolysis module, also called an electrolyzer stack, intended to carry out the reaction of production of di-hydrogen (H2) at the cathode, and dioxygen (02) at the anode resulting from the dissociation of water under the effect of the injection of a generally direct electric current into an alkaline solution, generally potassium hydroxide (KOH) or sodium hydroxide (NaOH). This water-electrolyte association is commonly called lye.

[0003] A diaphragm separates the anode from the cathode so that, under normal conditions, the molecules of dihydrogen and dioxygen cannot be mixed (except in very small proportions).

[0004] Downstream of the electrolytic module, the gas-liquid separation, between dihydrogen and lye on one side and dioxygen and lye on the other, is defined as a major step in the alkaline electrolysis process of water.

[0005] However, depending on the design of the gas-liquid separators, their efficiency is not total and not all gas bubbles manage to be extracted from the liquid phase in order to be eliminated by the appropriate orifice in the upper wall of the gas-liquid separator so that residual bubbles in the liquid phase can remain significantly.

[0006] However, in the current configuration of the separation system, the two liquid flows at the outlet of the gas-liquid separators are mixed before being reintroduced into the electrolysis module in a closed loop. A single pump allows the circulation of the lye within the elements of the electrolysis unit connected by a hydraulic circuit. Consequently, at the inlet of the electrolysis module, the cathode flow, which will be charged with dihydrogen during electrolysis, already contains bubbles of dioxygen dissolved in the lye. Similarly, the anodic flow, which will be charged with dioxygen, already contains bubbles of dihydrogen dissolved in the lye. Thus, at the outlet of the electrolysis module and at the inlet of the gas-liquid separators, the two flows are composed of a lye-dihydrogen-dioxygen mixture. However, the dihydrogen-dioxygen mixture is highly dangerous, which implies that the ratios of residual gases to gases produced by electrolysis must be kept below a threshold specified by the standards to reduce the risk of explosion.

[0007] Currently, the market is calling for the installation of flexible di-hydrogen and di-oxygen production plants that can adapt to intermittent renewable energy sources. This inevitably implies a capacity for operation at partial load of the electrolysis unit and no longer only at nominal load, which implies a loss of efficiency of the gas-liquid separator. In order to constantly keep the residual gas below the threshold specified by the standards, the current solution consists of limiting the operating range of the electrolysis unit according to the efficiency of the gas-liquid separator, for example to limit operation above 40% of the load in electric current intensity while maintaining a constant lye flow rate.Therefore, regardless of the operating load, the electrolysis steps in the electrolysis module and gas-liquid separation in the gas-liquid separators are carried out at constant lye flow rate while the production of dihydrogen and dioxygen varies.

[0008] The limitation of the operation of the electrolysis units of the prior art lies in the fact that the electrolysis unit becomes unusable below a certain charge threshold, that is to say when the electric current falls below a certain value. Summary of the invention

[0009] The invention proposes an electrolysis unit comprising: - a pump, - an electrolysis module comprising electrolytic cells held against each other in a stacking direction, the electrolysis module being crossed by a flow of lye coming from the pump and by an electric current, - a first gas-liquid separator dedicated to the separation of the dihydrogen-lye mixture from the electrolysis module, and - a second gas-liquid separator dedicated to the separation of the oxygen-lye mixture from the electrolysis module, the electrolysis unit further comprising: - at least one gas analyzer capable of providing information on the residual level of oxygen at the inlet or in the first gas-liquid separator or on the residual level of hydrogen at the inlet or in the second gas-liquid separator, - a control unit configured to receive and process the residual rate information sent by the gas analyzer and to provide a lye flow rate control based on the residual rate information, - a lye flow rate adapting means configured to receive the lye flow rate command and to adapt the lye flow rate according to the lye flow rate command.

[0010] According to other characteristics of the invention:

[0011] - the electrolysis unit comprises two gas analyzers including: a first gas analyzer at the inlet or in the first gas-liquid separator and capable of providing information on the residual level of oxygen defined by the ratio of the quantity of oxygen to the quantity of hydrogen, and a second gas analyzer at the inlet or in the second gas-liquid separator and capable of providing information on the residual level of dihydrogen defined by the ratio of the quantity of dihydrogen to the quantity of dioxygen;

[0012] - the means for adapting the lye flow rate is integrated into the pump so that the pump is able to adapt its operating speed according to the lye flow control;

[0013] - the electrolysis unit further comprises: at least one temperature sensor at the inlet of the first gas-liquid separator or at the inlet of the second gas-liquid separator, and at least one means for regulating the temperature of the lye flow at the outlet of the first gas-liquid separator or at the outlet of the second gas-liquid separator.

[0014] The invention also proposes a method for adapting the flow of lye within an electrolysis unit comprising: - a pump, - an electrolysis module comprising electrolytic cells held against each other in a stacking direction, the electrolysis module being crossed by a flow of lye coming from the pump and by an electric current, - a first gas-liquid separator reserved for the separation of the dihydrogen-lye mixture from the electrolysis module, and - a second gas-liquid separator reserved for the separation of the oxygen-lye mixture from the electrolysis module, - a control unit capable of determining measured or estimated residual rate information, the residual rate being a residual rate of oxygen at the inlet or in the first gas-liquid separator or a residual rate of hydrogen at the inlet or in the second gas-liquid separator, and of providing a lye flow rate control as a function of the residual rate information, and - a lye flow rate adapting means configured to receive the lye flow rate command and to adapt the lye flow rate according to the lye flow rate command, the process comprising the following steps: - determination of measured or estimated residual rate information by the control unit, - determination by the control unit of a lye flow rate command based on the residual rate information, - sending by the control unit of a lye flow command by means of lye flow adaptation.

[0015] According to other characteristics of the invention:

[0016] - the process is such that: if the residual rate is higher than a predetermined threshold value, the flow control tends to reduce the lye flow rate, or if the residual rate is lower than a predetermined threshold value, the flow control tends to increase the lye flow rate;

[0017] - the residual rate information comes from a measurement by: a first gas analyzer at the inlet or in the first gas-liquid separator and capable of providing information on the residual level of oxygen defined by the ratio of the quantity of oxygen to the quantity of hydrogen, or a second gas analyzer at the inlet or in the second gas-liquid separator and capable of providing information on the residual level of dihydrogen defined by the ratio of the quantity of dihydrogen to the quantity of dihydrogen;

[0018] - the residual rate information comes from an estimate by the control unit based on a mathematical calculation taking into account the value of the electric current intensity;

[0019] - the residual rate information comes from an estimate by the control unit based on an experimentally compiled database and establishing a correspondence between the value of the electric current intensity and the residual rate;

[0020] - the electrolysis unit further comprising: at least one temperature sensor at the inlet of the first gas-liquid separator or the second gas-liquid separator, and at least one means for regulating the temperature of the lye flow at the outlet of the first gas-liquid separator or at the outlet of the second gas-liquid separator, the method further comprises a temperature regulation of the lye flow comprising the following steps: reception by the control unit of temperature information from at least one temperature sensor, - determination by the control unit of a temperature command based on the temperature information, and sending by the control unit of the temperature control by means of temperature regulation. Brief description of the figures

[0021] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0022] [Fig-1] is a block diagram representing the arrangement and operation of an electrolysis unit according to a first embodiment of the invention;

[0023] [Fig.2] is a schematic representation of a gas-liquid separator showing the incoming and outgoing flows;

[0024] [Fig.3] is a block diagram representing the arrangement and operation of a electrolysis unit according to a second embodiment of the invention;

[0025] [Fig.4] is a block diagram representing the arrangement and operation of a electrolysis unit according to a third embodiment of the invention. Detailed description of the invention

[0026] In the following description, identical, similar or analogous elements will be designated by the same reference numbers.

[0027] The invention relates to an electrolysis unit 10 shown in [Fig.l]. The electrolysis unit 10 comprises an electrolysis module 14 comprising a stack of electrolytic cells held against each other in a stacking direction. The case described is that of alkaline electrolysis although the invention can be applied to other types of electrolysis or electrolysers.

[0028] The electrolytic cells of the electrolysis module 14 are connected in series from an electrical point of view and in parallel from a fluidic point of view. Each electrolytic cell is capable of carrying out the electrolysis of an electrolytic solution allowing the production of gaseous dihydrogen (H2) and dioxygen (02). The electrolysis carried out is a chemical reaction allowing the dissociation of water after injecting a generally direct electric current into an alkaline solution to obtain dihydrogen (H2) and dioxygen (02). The alkaline solution used is generally potassium hydroxide (KOH) or sodium hydroxide (NaOH). The alkaline solution comprises a combination of water and electrolyte, the electrolysis resulting from the dissociation of the solutes into ions. The solution obtained is commonly called lye.

[0029] In operation, the electrolysis module 14 is crossed by a flow of lye F. In order to allow the circulation of the flow of lye F in the electrolysis module 14, the electrolysis unit 10 comprises a single pump 12 arranged upstream of the electrolysis module 14.

[0030] The electrolysis module 14 is crossed by an electric current I. In the example, the electric current I comes from an electric generator 32. The electric current I passes through the electrolytic cells and thus allows the electrolysis of the alkaline solution to be carried out. To allow the generation of an electric current I, a voltage is applied to the terminals of the electrolysis module 14. The resulting electric current I depends on the electrical resistance of the electrolysis module 14, the number of electrolytic cells and the voltage of the cathodic and anodic reactions.

[0031] Under optimal operating conditions, the electrolysis module 14 works according to theoretically defined reference values, both for the electric current I and for the lye flow F entering the electrolysis module 14. The reference value of the electric current I and the reference value of the lye flow F are defined as a function of the sizing of the upstream pump 12 alone in order to obtain an optimal quantity of dihydrogen and dioxygen gas bubbles within the electrolysis module 14. Thus, the electric current I and the quantity of gas bubbles gravitating around the electrodes correspond to maximum efficiency.

[0032] The electrolysis module 14 has two hydraulic outputs, including: - a first outlet 16 dedicated to the cathodic flow transporting the dihydrogen molecules in the presence of the lye flow F, and - a second outlet 18 reserved for the anodic flow transporting the oxygen molecules still in the presence of the lye flow F.

[0033] To achieve gas-liquid separation, each hydraulic outlet of the electrolysis module is connected directly to a gas-liquid separator so that the flows of this mixture are introduced instantly into the appropriate gas-liquid separators.

[0034] The electrolysis unit 10 comprises two gas-liquid separators including: - a first gas-liquid separator 20 dedicated to the separation of the dihydrogen-lye mixture from the electrolysis module 14 and hydraulically connected to the first outlet 16, and - a second gas-liquid separator 22 dedicated to the separation of the oxygen-lye mixture from the electrolysis module 14 and hydraulically connected to the second outlet 18.

[0035] An example of a gas-liquid separator is shown in [Fig.2]. The gas (H2 or O2)-lye mixture is introduced into the dedicated gas-liquid separator through an inlet orifice 24.

[0036] Conventional gas-liquid separators operate on the principle of Archimedes' thrust which pushes the gas bubbles up to the gas-liquid interface 26 thanks to the difference in density between the gas bubbles (dihydrogen / dioxygen) and the liquid lye.

[0037] Gas-liquid separators have two outlets, including: - a first discharge 28 located on the upper face of the gas-liquid separator for the separated gas, and - a second discharge 30 located on a lower face of the gas-liquid separator for the residual liquid phase.

[0038] The residual liquid phases evacuated by the second evacuations 30 of the gas-liquid separators 20, 22 are reinjected into the single pump 12 and mixed in the latter 12 before being rerouted into the electrolysis module 14 at the outlet of the pump 12. The lye thus circulates within a closed circuit.

[0039] Consequently, at the inlet of the electrolysis module 14, the cathode flow, which will be charged with dihydrogen during electrolysis, already contains bubbles of dioxygen dissolved in the lye coming from the gas-liquid separator 22. Similarly, the anodic flow, which will be charged with dioxygen, already contains bubbles of dihydrogen dissolved in the lye coming from the gas-liquid separator 20. This is why, at the outlet of the electrolysis module 14 and at the inlet of the gas-liquid separators 20, 22, the two flows are composed of a lye-dihydrogen-dioxygen mixture. However, the mixture of dihydrogen and dioxygen gases can be dangerous because it is very easily flammable, or even explosive.

[0040] Also, residual rates are defined for each gas including: - a residual level of oxygen at the inlet or in the first gas-liquid separator 20, the residual level of oxygen being defined as the ratio between the quantity of oxygen gas and the quantity of hydrogen gas (O2 / H2), and - a residual level of dihydrogen at the inlet or in the second gas-liquid separator 22, the residual level of dihydrogen being defined as the ratio between the quantity of dihydrogen gas and the quantity of dioxygen gas (H2 / O2).

[0041] According to the principle of Archimedes' buoyancy, the larger the hydrogen or oxygen gas bubbles, the more efficient the gas-liquid separation. Similarly, the longer the residence time in the gas-liquid separators, the more the gas bubbles have the opportunity to rise to the free surface of the lye and the more efficient the gas-liquid separation.

[0042] Under nominal operating conditions, the gas-liquid separators operate optimally according to reference values ​​of lye flow rate and production of gaseous hydrogen and oxygen. When operating at partial load, i.e. with a current intensity lower than the value of the reference electric current intensity, the current values ​​of production of hydrogen and oxygen will be lower than the nominal values, inducing a reduction in the volume of hydrogen bubbles in the cathode flow as well as the volume of oxygen in the anode flow. As a result, the flow rates of the anode and cathode flows are no longer optimal for the operation of the gas-liquid separators, which results in a reduction in the efficiency of the gas-liquid separators and a possible exceeding of the thresholds specified by the standards with regard to the residual gas ratios.Exceeding the residual gas thresholds defined by the standards automatically results in the electrolysis unit being shut down.

[0043] The invention proposes a control loop making it possible to modulate the flow of lye in order to extend the operating ranges of the electrolysis module 14, in particular for operation at very low partial load, i.e. with an electric current intensity lower than the value of the reference electric current intensity. The invention also makes it possible to increase the efficiency of the electrolysis module 14, in particular at partial load.

[0044] According to particular features of the invention shown in [Fig. 1] and with a view to implementing a control loop, the electrolysis unit 10 further comprises: - a first gas analyzer 34 capable of providing information on the residual level of oxygen in the first gas-liquid separator 20, - a second gas analyzer 36 capable of providing information on the residual level of dihydrogen in the second gas-liquid separator 22, - a control unit 38 configured to receive and process the information sent by the gas analyzers 34, 36 and to provide a lye flow rate control, - a lye flow rate adapting means configured to receive the lye flow rate command and to adapt the lye flow rate according to the lye flow rate command.

[0045] In the example shown, the means for adapting the lye flow rate is integrated into the single pump 12 so that the single pump 12 is able to adapt its operating speed as a function of the lye flow rate command.

[0046] In particular, the single pump 12 is a single speed-regulated pump offering a wide flow rate range and allowing a wide operating range of the electrolysis unit 10.

[0047] Alternatively, the means for adapting the lye flow rate may be a flow regulator separate from the pump 12 alone. For example, the lye flow regulator may be a diaphragm having a variable section opening.

[0048] In the example of [Fig.l], the electrolysis unit 10 comprises two gas analyzers 34, 36 but it is possible to envisage a variant in which the electrolysis unit 10 comprises only one gas analyzer among the two gas analyzers 34 and 36.

[0049] Furthermore, each gas analyzer 34, 36 can be placed in the corresponding gas-liquid separator 20, 22, in other words on the dedicated gas outlets or at the inlet of the latter 20, 22 or between the outlet of the electrolysis module 14 and the inlet of the gas-liquid separator 20, 22. The gas analyzer 34, 36 can also be placed in another location within the electrolysis unit 10.

[0050] In [Fig.l], the dotted lines represent information flows. More specifically, the spaced dotted lines represent measurement information and the tightly spaced dotted lines represent control information. The solid lines represent have lye transport pipes and the double line at the input of the electrolysis module 14 represents the electrical power supply providing the electrical current I to the electrolysis module 14.

[0051] The arrangement of the electrolysis unit 10 allows the implementation of a control loop which acts on the flow rate of lye F through the control of the means for adapting the flow rate of lye F as a function of the information provided by: - the first gas analyzer 34, and - the second gas analyzer 36.

[0052] This control loop is fully automated, meaning that human intervention at the electrolysis module 14 is not required, thereby eliminating a potential hazard associated with human intervention.

[0053] The control loop is implemented by the control unit 38. The control unit 38 is for example a PLC, a computer, a computing unit or a microcontroller. The control unit 38 receives and processes information from: - of the first gas analyzer 34, and - of the second gas analyzer 36.

[0054] The information can be received continuously by the control unit 38.

[0055] Depending on the information received, the control unit 38 determines and sends a flow command intended for the pump 12 alone.

[0056] The control loop is implemented by the control unit 38 according to a closed loop which is repeated cyclically with a predetermined periodicity or according to predefined occurrences.

[0057] The control unit 38 is managed and manipulated by human intervention remotely from the electrolysis module 14.

[0058] The first element analyzed by the control unit 38 is a residual gas level.

[0059] Thus, when an increase in the residual gas levels of dihydrogen or dioxygen is detected by the control unit 38, a flow command is sent by the control unit 38 in order to lower the lye flow rate. The speed of the anodic and cathodic flows within the gas-liquid separators 20, 22 is then reduced, which allows: - to optimize the time spent by the flows in the gas-liquid separators 20, 22, and - to promote coalescence, that is to say the fusion of gas bubbles and their rise towards the gas-liquid interface of the gas-liquid separators 20, 22.

[0060] The efficiency of the gas-liquid separators 20, 22 is thus improved even under partial load, which makes it possible on the one hand to keep the residual gases below the thresholds specified by the standards and on the other hand to widen the operating range of the electrolysis unit 10 towards lower loads.

[0061] In addition to this improvement in the efficiency of the gas-liquid separators 20, 22, the increase in the density of the gas bubbles within the lye increases the electrical resistance of this two-phase mixture, due to the gases being more electrically resistive. Thus, the anodic and cathodic flows are more electrically resistive, which reduces the leakage currents, commonly called "Shunt currents", between the different electrolytic cells. Consequently, the electrochemical efficiency of the electrolysis module 14 is improved by increasing the Faraday efficiency, in other words its effective operating range is further expanded. Note that the lower and upper limits of operability are also linked to the thermal aspects because it is the lye circuit which makes it possible to evacuate the heat produced by the Joule effect in the electrolyzer stack.

[0062] Of course, monitoring of the residual rate thresholds is maintained. At each instant, the residual rates are measured using the analyzers located in the gas-liquid separators 20, 22 and are systematically compared to reference values ​​linked to the maximum thresholds dictated by the standards. As soon as the measured values ​​are similar to values ​​higher than those theoretically authorized, the control unit 38 sends a flow command to the adjustable lye pump to adapt the value of the lye flow entering the electrolysis module 14 in order to maintain the residual rates below the set thresholds.

[0063] Conversely, when the load of the electrolysis unit 10 increases, that is to say when the intensity of the electric current I increases, the residual rates tend to decrease and to pass below the reference values ​​of residual rates. In this case, the control unit 38 sends a command to increase the flow rate in order to approach the nominal values ​​allowing maximum efficiency for a larger load.

[0064] The method of the invention therefore comprises the following steps: - determination of residual rate information by the control unit 38, - determination by the control unit 38 of a lye flow rate command as a function of the residual rate information, - sending by the control unit 38 of a lye flow rate command by means of adapting the lye flow rate, in this case to the controllable pump.

[0065] In particular, the control unit 38 determines the lye flow rate control so that: - if the residual rate is higher than a predetermined threshold value, the lye flow control tends to reduce the lye flow, and - if the residual rate is lower than a predetermined threshold value, the lye flow control tends to increase the lye flow.

[0066] According to an effect resulting from the reduction of the lye flow rate, the temperature within electrolysis unit 10 tends to increase since fewer calories are evacuated by the lye flow. It is therefore necessary to provide a drop in the temperature of the anodic and cathodic flows at the inlet of the electrolysis module 14 in order to maintain a constant average temperature, in other words it is the outlet temperature of the stack which must be constant.

[0067] Under partial load, the average temperature of the lye within the electrolysis module 14 decreases, which also implies a decrease in the electrical conductivity of the lye. The lower conductivity makes it possible to reduce leakage currents and tends to improve efficiency in accordance with what has been described above.

[0068] In order to regulate the temperature of the lye within the electrolysis unit 10, the electrolysis unit 10 comprises: - a first temperature sensor 40 at the inlet of the first gas-liquid separator 20, which corresponds to the outlet of the electrolyser stack on the anode side, - a second temperature sensor 42 at the inlet of the second gas-liquid separator 22, which corresponds to the outlet of the electrolyzer stack on the cathode side and - a first means 44 for regulating the temperature of the lye flow at the outlet of the first gas-liquid separator 20, and - a second means 46 for regulating the temperature of the lye flow at the outlet of the second gas-liquid separator 22.

[0069] Alternatively, it is possible to envisage a single temperature sensor positioned at any point in the lye hydraulic circuit. It is also possible to envisage a single means of regulating the temperature downstream of the single pump 12 and upstream of the electrolysis module 14.

[0070] Each temperature regulation means 44, 46 is for example a heat exchanger.

[0071] Concretely, the lye temperature is measured continuously in order to compare it to a reference temperature. If the measured value of the lye temperature is different from the value of the reference temperature, either because it is higher or because it is lower, the control unit 38 will send a signal in order to adapt the value of said lye temperature entering the electrolysis module 14 in order to approach the value of the reference temperature at the outlet of the electrolysis module 14. Thanks to this adjustment of the value of the temperature of the lye at the outlet of the gas-liquid separators 20, 22 and therefore at the inlet of the electrolysis module 14, the value of the temperature of the lye at the outlet of the electrolysis module 14 will therefore be adapted so that it reaches the value of the reference temperature.

[0072] Temperature regulation involves the following steps: - reception by the control unit 38 of temperature information from a temperature sensor, - determination by the control unit 38 of a temperature command as a function of the temperature information, and - sending, by the control unit 38, the temperature command to the temperature regulation means corresponding to the temperature sensor. The first temperature sensor 40 corresponding to the first temperature regulation means 44 and the second temperature sensor 42 corresponding to the second temperature regulation means 46.

[0073] According to variants of the invention shown in Figures 3 and 4, the residual rate information can come from an estimate by the control unit 38 based on a mathematical calculation taking into account the value of the electric current intensity I.

[0074] Indeed, the electrolysis unit 10 can be completed by at least one electrical intensity indicator 48 as shown in [Fig. 3]. The electrical intensity indicator 48 is for example integrated into the electrical generator 32. The information on the electrical current intensity I is sent to the control unit 38 and allows more predictive control of the electrolysis unit 10 and of the effects of a change in the electrical current intensity I on the residual gas levels in the gas-liquid separators 20, 22. The adaptation of the lye flow rate is thus faster as a function of the electrical current intensity I entering the electrolysis module 14, while being controlled by the measurements of the residual gas levels. This measurement of the electrical current intensity I is directly linked to the production volume of hydrogen and oxygen gas bubbles by Faraday's law, and depends on the operating load.At any time, it is possible to measure the value of the intensity of the electric current I. When this measured value of the intensity of the electric current I is different from the nominal value during operation at partial load, the control unit 38 will send a signal to the single pump 12 to adapt the value of the flow of lye entering the electrolysis module 14.

[0075] For example, the residual rate information may come from an estimate by the control unit 38 based on an experimentally constructed database establishing a correspondence between the value of the electric current intensity I and the residual rate. In this case, it is possible to eliminate the gas analyzers 34, 36 as shown in [Fig.4]. Indeed, thanks to a learning process, the programmable logic unit can use an approach linking these residual rates to the variations in the electric current intensity I. Thus, the lye flow rate is automatically adapted by the control loop according to the changes in the electric current intensity I entering the electrolysis module 14.

[0076] This embodiment of the invention is said to be preferential but it is entirely possible to have several electrolysis units consisting of several electrolysis modules, gas-liquid separators, controllable pumps, cooling systems lye and power conversion units arranged in series and / or parallel. Each can appear horizontally, vertically or a combination of both orientations, regardless of the arrangement studied. The same is true with regard to the number of electrolytic cells inside the electrolysis module(s), namely that the defined approach is independent of the number of electrolytic cells studied.

[0077] Similarly, this embodiment can be applied to completely separate anodic and cathodic lye circuits, including independent pumps and independent lye cooling systems. At least two temperature sensors will then be required, namely at least one on each lye circuit.

[0078] The invention has several technical advantages presented below.

[0079] The invention makes it possible to avoid stopping an electrolysis unit during partial load operation by avoiding reaching the residual rate thresholds.

[0080] The invention also makes it possible to broaden the operating range of an electrolysis unit, in particular by allowing settings allowing operation below a load of 40% in electric current intensity.

[0081] The invention makes it possible to reduce the risks linked to the mixing of H2 and O2 gases within an electrolysis unit.

[0082] The invention also makes it possible to improve the efficiency of an electrolysis unit.

[0083] The invention allows more automated operation of an electrolysis unit and faster adjustments thanks to anticipation of parameter changes.

Claims

Claims

1. Electrolysis unit (10) comprising: - a pump (12), - an electrolysis module (14) comprising electrolytic cells held against each other in a stacking direction, the electrolysis module (14) being crossed by a flow of lye (F) coming from the pump (12) and by an electric current (I), - a first gas-liquid separator (20) dedicated to the separation of the dihydrogen-lye mixture coming from the electrolysis module (14), and - a second gas-liquid separator (22) dedicated to the separation of the dioxygen-lye mixture coming from the electrolysis module (14), the electrolysis unit (10) being characterized in that it further comprises: - at least one gas analyzer capable of providing information on the residual level of dioxygen at the inlet or in the first gas-liquid separator (20) or on the residual level of dihydrogen at the inlet or in the second separator gas-liquid (22),- a control unit configured to receive and process the residual rate information sent by the gas analyzer and to provide a lye flow rate command based on the residual rate information, - a lye flow rate adaptation means configured to receive the lye flow rate command and to adapt the lye flow rate based on the lye flow rate command.,

2. Electrolysis unit (10) according to claim 1, characterized in that it comprises two gas analyzers including: - a first gas analyzer at the inlet or in the first gas-liquid separator (20) and capable of providing information on the residual level of dioxygen defined by the ratio of the quantity of dioxygen to the quantity of dihydrogen, and - a second gas analyzer at the inlet or in the second gas-liquid separator (22) and capable of providing information on the residual level of dihydrogen defined by the ratio of the quantity of dihydrogen to the quantity of dioxygen.

3. Electrolysis unit (10) according to any one of the preceding claims, characterized in that the means for adapting the lye flow rate is integrated in the pump (12) so that the pump (12) is able to adapt its operating speed according to the command of lye flow.

4. Electrolysis unit (10) according to any one of the preceding claims, characterized in that it further comprises: - at least one temperature sensor (40) at the inlet of the first gas-liquid separator (20) or at the inlet of the second gas-liquid separator (22), and - at least one means for regulating the temperature of the lye flow at the outlet of the first gas-liquid separator (20) or at the outlet of the second gas-liquid separator (22).

5. Method for adapting the flow of lye within an electrolysis unit (10) comprising: - a pump (12), - an electrolysis module (14) comprising electrolytic cells held against each other in a stacking direction, the electrolysis module (14) being crossed by a flow of lye (F) coming from the pump (12) and by an electric current (I), - a first gas-liquid separator (20) reserved for the separation of the dihydrogen-lye mixture coming from the electrolysis module (14), and - a second gas-liquid separator (22) reserved for the separation of the dioxygen-lye mixture coming from the electrolysis module (14), - a control unit (38) capable of determining measured or estimated residual rate information, the residual rate being a residual rate of dioxygen at the inlet or in the first gas-liquid separator (20) or a residual rate of dihydrogen at the inlet or in the first gas-liquid separator (20) or a residual rate of dihydrogen at the inlet or in the first gas-liquid separator (20) or a residual rate of dioxygen at the inlet or in the second gas-liquid separator (2 ... the inlet or in the second gas-liquid separator (22),and providing a lye flow rate command as a function of the residual rate information, and - a lye flow rate adaptation means configured to receive the lye flow rate command and to adapt the lye flow rate as a function of the lye flow rate command, the method being characterized in that it comprises the following steps: - determination of measured or estimated residual rate information by the control unit (38), - determination by the control unit (38) of a lye flow rate command as a function of the residual rate information, - sending by the control unit (38) of a lye flow rate command to the lye flow rate adaptation means.,

6. Method according to claim 5, characterized in that: - if the residual rate is greater than a predetermined threshold value, the flow control tends to reduce the lye flow rate, or - if the residual rate is below a predetermined threshold value, the flow control tends to increase the lye flow rate.

7. Method according to any one of claims 5 or 6, characterized in that the residual rate information comes from a measurement by: - ​​a first gas analyzer at the inlet or in the first gas-liquid separator (20) and capable of providing information on the residual rate of dioxygen defined by the ratio of the quantity of dioxygen to the quantity of dihydrogen, or - a second gas analyzer at the inlet or in the second gas-liquid separator (22) and capable of providing information on the residual rate of dihydrogen defined by the ratio of the quantity of dihydrogen to the quantity of dihydrogen.

8. Method according to any one of claims 5 or 6, characterized in that the residual rate information comes from an estimate by the control unit (38) based on a mathematical calculation taking into account the value of the electric current intensity (I).

9. Method according to any one of claims 5 or 6, characterized in that the residual rate information comes from an estimate by the control unit (38) based on a database created experimentally and establishing a correspondence between the value of the electric current intensity (I) and the residual rate.

10. Method according to any one of claims 5 to 9, characterized in that the electrolysis unit (10) further comprising: - at least one temperature sensor at the inlet of the first gas-liquid separator (20) or of the second gas-liquid separator (22), and - at least one means for regulating the temperature of the lye flow at the outlet of the first gas-liquid separator (20) or at the outlet of the second gas-liquid separator (22), the method further comprises a temperature regulation of the lye flow comprising the following steps: - reception by the control unit (38) of temperature information from the at least one temperature sensor, - determination by the control unit (38) of a temperature command as a function of the temperature information, and - sending by the control unit (38) of the temperature command by means of temperature regulation.

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