METHOD AND SYSTEM FOR DETECTING DAMAGE IN ELECTROCHEMICAL CELLS USING INERT GAS INJECTION AND DYNAMIC DIFFERENTIAL PRESSURE ANALYSIS

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority on U.S. Patent Application No. 63/431,857 filed Dec. 12, 2022, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to industrial electrolyzers and more particularly to the identification of damaged electrolysis cell membranes prior to starting the full operation cycle.

BACKGROUND OF THE ART

An electrochemical cell (also referred to herein as a “cell”) is a device where a chemical decomposition reaction takes place by applying an electrical current. Such a device is used to decompose Salt (NaCl) to Caustic (NaOH) and Chlorine (Cl₂). It is also used to decompose Potassium Chloride into Potassium Hydroxide and Chlorine. Similar processes, such as water electrolysis used to produce Hydrogen, are also performed using electrochemical cells.

In an industrial setting, several cells are combined in series or parallel to perform the reaction. This combination is called an electrolyzer. Most industrial electrochemical cells are composed of two electrodes (anode and cathode) and a membrane. In some contexts, the membrane may also be referred to as a separator, a cell separator, a cell membrane, an exchange membrane, or an ion exchange membrane. When cations are exchanged across the membrane, the membrane may be referred to as a cation exchange membrane. An oxidation reaction takes place at the anode and a reduction reaction occurs at the cathode. In modern electrochemical cells, membranes such as ion exchange membranes are used to let only desirable ions migrate from one side of the reaction (anode) to the other side (cathode). The efficiency and safety of industrial electrochemical cell operation is related mainly to the safety and efficiency of its components. More particularly, it is related to the safety and efficiency of the cation exchange membrane. Despite their efficiency and environmentally-friendly characteristic, cation exchange membranes are sensitive to contaminants above allowed concentrations in the inlets and to mechanical defects during installation or manipulation. Cation exchange separation efficiency is severely affected by the occurrence of small holes or tears (also referred to as pinholes or pores). Some reasons for the presence of pinholes in the cell membrane are the formation of voids, blisters, and delaminating of the membrane due to mechanical stress during maintenance, and by contaminated electrolytes mainly during shutdown and startup operation modes. The presence of pinholes in the membrane, for example, can affect the cell's efficiency in different ways depending on the size and location of the pinhole(s) (e.g., in a part of the cell where there is the liquid or in another part of the cell where only gas is present), as well as the age of the cell. Pinholes may decrease the membrane separation capability to prevent back migration of hydroxyl ions to the anolyte compartment. Usually, pinhole effects are not detectable during normal operation unless corrosion has taken place in the anode coating due to the attack of caustic soda in the case of the chlor alkali electrolysis process. However, pinhole effects are noticeable at start-up or shut down because of their effect on the cell voltage. A failure of the separation efficiency of the ion exchange membrane(s) may lead to the mixing of gases like H₂ and Cl₂ or H₂ and O₂, which can explode, or the leaking of electrolytes that are fatal to humans and harmful for the environment.

The detection of damaged membranes by analyzing the current-voltage-curves during the startup of an electrolyzer as well as after a shutdown is well known. But starting the production of gases bears already the risk of mixing in case of damaged membranes and can lead to an explosion. Currently no method is known to guarantee that at the moment of energizing an electrolyzer no explosive mixture of gases from the anode and cathode sides can be formed. Well-known membrane leak tests can only be performed when the electrolyzer is drained or the electrolyte circulation is stopped.

Thus, there is a need for improved methods for the detection of damaged membranes prior to the electrolyzer being energized, i.e. prior to the production of gases which might form explosive mixtures.

SUMMARY

In accordance with a broad aspect, there is provided a damage detection method for an electrolyzer having a plurality of electrolysis cells, the method comprising obtaining, during a shutdown of the electrolyzer, one or more first voltage measurements for each of the plurality of cells, performing, based on the one or more first voltage measurements, a first classification of the plurality of cells into a first category of cells with a damaged membrane and a second category of cells without the damaged membrane, executing one or more first tests in the electrolyzer to confirm whether the first category of cells comprises at least one cell, at least one of the one or more first tests being based on an injection of inert gases at an anode and at a cathode of each of the plurality of cells of the, determining that an outcome of the one or more first tests confirms that the first category of cells comprises the at least one cell, causing a replacement of the at least one cell and executing a second test in the electrolyzer to assess whether at least one further cell having the damaged membrane remains in the electrolyzer, determining that an outcome of the second test indicates that the at least one further cell having the damaged membrane remains in the electrolyzer, causing the electrolyzer to stop, and repeating the executing of the one or more first tests, the causing the replacement of the at least one cell having the damaged membrane, and the executing of the second test, and determining that the outcome of the second test indicates that no further cell having the damaged membrane remains in the electrolyzer, and causing a start of the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, the method further comprises executing the second test upon determining that the outcome of the one or more first test fails to confirm that the first category of cells comprises the at least one cell having the damaged membrane.

In at least one embodiment in accordance with any previous/other embodiment described herein, the performing the first classification of the plurality of cells comprises determining a cell current efficiency of the electrolyzer during the shutdown of the electrolyzer, the cell current efficiency determined as a function of a time taken for a voltage level of each cell of the electrolyzer to reach a pre-determined occurrence in a voltage curve after a polarization current has been triggered in the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, the determining the cell current efficiency comprises using a formula having a form of:

• • CE %=f(Δt), where CE % is the cell current efficiency for each cell of the electrolyzer, Δt is the time taken for the voltage level of each cell to switch from chlorine electrolysis to water electrolysis, and f is a parametrical non-linear function.

In at least one embodiment in accordance with any previous/other embodiment described herein, the method further comprises, subsequent to performing the first classification of the plurality of cells, triggering an alarm indicative of detection of the first category of cells with the damaged membrane.

In at least one embodiment in accordance with any previous/other embodiment described herein, the method further comprises initiating a maintenance of the electrolyzer subsequent to performing the first classification of the plurality of cells.

In at least one embodiment in accordance with any previous/other embodiment described herein, the method further comprises, subsequent to causing the start of the electrolyzer, obtaining, during the start of the electrolyzer, one or more second voltage measurements for each of the plurality of cells of the electrolyzer, performing, based on the one or more second voltage measurements, a second classification of the plurality of cells into the first category of cells with the damaged membrane and the second category of cells without the damaged membrane, assessing whether the first category of cells comprises at least one cell, determining that the first category of cells comprises the at least one cell, causing the electrolyzer to stop, and repeating the causing the replacement of the at least one cell and the executing the second test to assess whether at least one further cell having the damaged membrane remains in the electrolyzer, and determining that the first category of cells fails to comprise the at least one cell, and proceeding with normal operation of the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, performing the second classification of the plurality of cells comprises determining a cell current efficiency of the electrolyzer during the start of the electrolyzer, the cell current efficiency determined based on a look up table correlating a current efficiency range of each cell the electrolyzer with a time taken by each cell to produce chlorine after a polarization current has been triggered in the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, each cell of the electrolyzer comprises at least the cathode, the anode, and a membrane between the cathode and the anode, and executing the second test comprises injecting a first inert gas at the cathode of each cell of the electrolyzer, injecting a second inert gas at the anode of each cell of the electrolyzer, and comparing a concentration rate of change of inert gas mixture at an anolyte outlet of the electrolyzer to a concentration rate of change threshold, and for a given cell of the electrolyzer, the concentration rate of change of inert gas mixture being greater than the concentration rate of change threshold is indicative of the membrane of the given cell being damaged, and a position of the given cell is determined based on a time taken by the concentration rate of change of inert gas mixture to exceed the concentration rate of change threshold.

In at least one embodiment in accordance with any previous/other embodiment described herein, the plurality of cells of the electrolyzer are one of a plurality of chlor-alkali electrolysis cells and a plurality of non-alkaline water electrolysis cells.

In accordance with yet another broad aspect, there is provided an assembly comprising a plurality of electrolysis cells forming one or more electrolyzers, and a damage detection system comprising at least one computing device operatively coupled to the one or more electrolyzers, the at least one computing device comprising at least one processing unit and a non-transitory computer readable medium having stored thereon program instructions executable by the at least one processing unit for obtaining, during a shutdown of the electrolyzer, one or more first voltage measurements for each of the plurality of cells, performing, based on the one or more first voltage measurements, a first classification of the plurality of cells into a first category of cells with a damaged membrane and a second category of cells without the damaged membrane, executing one or more first tests in the electrolyzer to confirm whether the first category of cells comprises at least one cell, at least one of the one or more first tests being based on an injection of inert gases at an anode and at a cathode of each of the plurality of cells of the electrolyzer, determining that an outcome of the one or more first tests confirms that the first category of cells comprises the at least one cell, causing a replacement of the at least one cell, and executing a second test in the electrolyzer to assess whether at least one further cell having the damaged membrane remains in the electrolyzer, determining that an outcome of the second test indicates that the at least one further cell having the damaged membrane remains in the electrolyzer, causing the electrolyzer to stop, and repeating the executing of the one or more first tests, the causing the replacement of the at least one cell having the damaged membrane, and the executing of the second test, and determining that the outcome of the second test indicates that no further cell having the damaged membrane remains in the electrolyzer, and causing a start of the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, the one or more first voltage measurements are obtained from at least one data acquisition and transmission (DAT) module communicatively coupled to the plurality of cells, the at least one DAT module configured to measure voltages of the plurality of cells.

In at least one embodiment in accordance with any previous/other embodiment described herein, the instructions are further executable by the at least one processing unit for executing the second test upon determining that the outcome of the one or more first test fails to confirm that the first category of cells comprises the at least one cell having the damaged membrane.

In at least one embodiment in accordance with any previous/other embodiment described herein, the instructions are executable by the at least one processing unit for performing the first classification of the plurality of cells comprising using a cell classification and damage detection module communicatively coupled to the at least one DAT module for determining a cell current efficiency of the electrolyzer during the shutdown of the electrolyzer, the cell current efficiency determined as a function of a time taken for a voltage level of each cell of the electrolyzer to reach a pre-determined occurrence in a voltage curve after a polarization current has been triggered in the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, the instructions are executable by the at least one processing unit for determining the cell current efficiency using a formula having a form of:

• • CE %=f(Δt), where CE % is the cell current efficiency for each cell of the electrolyzer, Δt is the time taken for the voltage level of each cell to switch from chlorine electrolysis to water electrolysis, and f is a parametrical non-linear function.

In at least one embodiment in accordance with any previous/other embodiment described herein, the instructions are further executable by the at least one processing unit for, subsequent to performing the first classification of the plurality of cells, triggering an alarm indicative of detection of the first category of cells with the damaged membrane and/or initiating a maintenance of the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, the instructions are further executable by the at least one processing unit for, subsequent to causing the start of the electrolyzer, obtaining, during the start of the electrolyzer, one or more second voltage measurements for each of the plurality of cells of the electrolyzer, performing, based on the one or more second voltage measurements, a second classification of the plurality of cells into the first category of cells with the damaged membrane and the second category of cells without the damaged membrane, assessing whether the first category of cells comprises the at least one cell, determining that the first category of cells comprises the at least one cell, causing the electrolyzer to stop, and repeating the causing the replacement of the at least one cell and the executing the second test to assess whether at least one further cell having the damaged membrane remains in the electrolyzer, and determining that the first category of cells fails to comprise the at least one cell, and proceeding with normal operation of the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, the instructions are executable by the at least one processing unit for performing the second classification of the plurality of cells comprising determining a cell current efficiency of the electrolyzer during the start of the electrolyzer, the cell current efficiency determined based on a look up table correlating a current efficiency range of each cell the electrolyzer with a time taken by each cell to produce chlorine after a polarization current has been triggered in the electrolyzer.

In at least one embodiment in accordance with any previous/other embodiment described herein, each cell of the electrolyzer comprises at least the cathode, the anode, and a membrane between the cathode and the anode, and the instructions are executable by the at least one processing unit for executing the second test comprising using an inert gas leak test system coupled to the plurality of cells for injecting a first inert gas at the cathode of each cell of the electrolyzer, injecting a second inert gas at the anode of each cell of the electrolyzer, and comparing a concentration rate of change of inert gas mixture at an anolyte outlet of the electrolyzer to a concentration rate of change threshold, and, for a given cell of the electrolyzer, the concentration rate of change of inert gas mixture being greater than the concentration rate of change threshold is indicative of the membrane of the given cell being damaged, and a position of the given cell is determined based on a time taken by the concentration rate of change of inert gas mixture to exceed the concentration rate of change threshold.

In at least one embodiment in accordance with any previous/other embodiment described herein, the plurality of cells are one of a plurality of chlor-alkali electrolysis cells and a plurality of non-alkaline water electrolysis cells

Features of the systems, devices, and methods described herein may be used in various combinations, in accordance with the embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures,

FIGS. 1A and 1B are flowcharts of a method for detecting damaged membranes in electrochemical cells using inert gas injection;

FIG. 2A is a schematic diagram of a system for performing an inert gas leak test; and

FIG. 2B is a plot of helium gas concentration at the anolyte outlet header of FIG. 2A over time, since the start of injection of helium gas at the catholyte outlet header of FIG. 2A;

FIG. 3 is a schematic diagram of a system for electrolysis cell voltage measurement and classification;

FIG. 4 is a block diagram of an example computing system for implementing the method of FIGS. 1A and 1B and/or the system of FIG. 3;

FIGS. 5A, 5B, 5C, and 5D are diagrams of cell voltage and current profiles during electrolyzer startup and shutdown.

It will be noticed that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

Four methods are commonly used to detect damaged membranes to avoid H₂/Cl₂— or H₂/O₂— explosions or leaking electrolysis cells. As used herein, the term “damaged” (or “damage”), when used in relation to the membrane (e.g., a cation exchange membrane) of an electrochemical cell, refers to a membrane that is severely defective or faulty. As used herein, a damaged membrane may be defined as a membrane that contains pinholes which decrease the membrane's separation capability. By back migration of hydroxyl ions to the cells anolyte compartment, product is lost. Also, hydrogen can enter the anodic compartment and form an explosive mixture with the chlorine.

In the first method, a differential pressure is applied across the membrane with nitrogen gas (N₂). All valves are closed. A fast decrease of the differential pressure indicates a membrane damage. However, this test cannot identify which membrane needs to be replaced for all operating cells and the method is difficult to automate. This test also interrupts and delays the usual startup procedure. All operations such as flowing, or heating electrolytes should be stopped. Since the electrolyzer is not empty, only large membrane damages at the very top of the membrane can be detected. In operation, the liquid level in the electrolyzer decreases on the cathode side by 10% and more. Therefore, undetected holes, by this test, become in operation a safety risk.

In the second method, Nitrogen (N₂) is applied to the catholyte side of the empty electrolyzer. All valves are closed. If a fast decrease of the differential pressure indicates a membrane damage, the gas exchange between cells on the anode side is prohibited by flooding the inlet or outlet headers, while the other cell connection is individually connected with a device to measure the flow rate of the leaking gas or the pressure, etc. Due to the costs to automate all involved hand valves, this test is performed manually. In addition, this method delays the startup by hours with high corresponding production loss. In particular, the initial analysis of the overall electrolyzer differential pressure decrease often leads to false positive detections if several membranes have small non-critical damages.

In the third method, the electrolyzer is started with high nitrogen gas feed to dilute generated hydrogen to the extent that, in case of mixing with the gas from the anode, the explosion limit is not exceeded. At the anolyte outlet header, the hydrogen concentration is analyzed. This test is usually automated. Still, this test cannot identify which cells have damaged membranes and need to be replaced. The residual risk for explosions depends on the response time of the analyzer. Since the electrolyzer is not empty, only large membrane damages at the very top of the membrane can be detected. In operation, the liquid level in the electrolyzer decreases on the cathode side between low load and high load operation by 10% and more. Therefore, undetected holes, by this test, become in operation a safety risk.

In the fourth method, after a shutdown, cell voltages with damaged membranes decrease faster and during a startup increase later than compared to cells with non-damaged membranes. This method is sensitive and allows for a precise classification of individual membrane performance and consequently for applying adequate countermeasures. This test can be easily automated. However, it requires stopping or starting the electrolyzer and does not completely suppress the risk of starting the electrolyzer with damaged membranes after the shutdown. A startup with damaged membranes is only safe if enough nitrogen is applied to dilute the hydrogen. The safe volume flow of nitrogen cannot be predicted as it depends on the number of damaged membranes and on the severity of the individual membrane damages.

Chlor-Alkali plants may combine different methods, depending on assumed risk of having damaged membranes. For example, if an electrolyzer shutdown is performed without abnormal pressure or differential pressure and no alarms occurred from the above-described fourth method during shutdown, the electrolyzer may then be started with the fourth method only. On the other hand, if an electrolyzer shutdown is not optimally controlled (e.g., due to inadequate control of pressures, etc.), the above-described first method may be applied and in case the first method fails, the second method may then be applied; otherwise the electrolyzer is started using the fourth method.

Described herein are methods and systems to detect defects (i.e. damage) in ion exchange membrane(s) operated in an industrial scale electrolyzer, such as a chlor alkali electrolyzer. It should be understood that the methods and systems described herein may also be used to detect damage in cell separators. The proposed method is based on an inert leak gas analysis, preferably Helium (He). In one embodiment, the method may be used during preparation for electrolyzer startup, filling or heating up operation mode. Helium may be fed via a nitrogen purge line to the cathode side analyzed at an anolyte outlet header of the electrolyzer. If the helium concentration is above a given (pre-determined) concentration threshold, the systems and methods described herein cause the startup of the electrolyzer to be automatically blocked. In this manner, it may be possible to ensure precise determination of the maximum expectable peak concentration of hydrogen in the electrolyzer's anode header at startup. Monitoring the leak rate of the He/N₂-mixture from cathode to anode side during the filling of the electrolyzer also allows the prediction of the expectable peak concentrations between startup and full load operation.

In one embodiment, the proposed method may prevent the operation of an industrial electrolyzer with defective membranes before starting the production of gases. This is in contrast to existing leak test methods, which may only be executed when the electrolyzer is drained or the electrolytes circulation is stopped.

FIGS. 1A and 1B depict a method 100 for detecting damaged membranes in operating electrolyzers, in accordance with one embodiment. At step 102, voltage measurements (referred to herein as “first voltage measurements”) are obtained in real-time or pseudo real-time at each operating cell of the electrolyzer, during load decrease (i.e. during the shutdown of the electrolyzer). The voltage measurements may be obtained using one or more data acquisition devices such as one or more data Acquisition and Transmission (DAT) modules 301, which will be described further below with reference to FIG. 3. The data acquisition device(s) may in addition sense the main electrolyzer current and obtain process measurements such as, but not limited to, electrolyzer brine inlet pH and electrolyzer feed brine flow [m³/h]. At step 104, data obtained at step 102 is analyzed to classify and detect operating cells with damaged membrane(s). A first classification of the plurality of cells into a first category of cells with a damaged membrane and a second category of cells without the damaged membrane is performed at step 104, based on the one or more first voltage measurements. Step 104 may be performed using a computer device, such as the cell classification and damage detection module 303, which will be described further below with reference to FIG. 3. As will also be described further below with reference to FIGS. 5A and 5B, in one embodiment, the step 104 of classifying and detecting damaged membrane(s) (during the electrolyzer's shutdown operation mode) may be based on the approximation of the electrolyzer's single cell current efficiency, using the time duration taken to reach a minimum voltage threshold.

At step 106, an indication as to the presence of damaged membrane(s) may be output, e.g., an alarm indicative of detection of the damaged membrane(s) may be triggered if damaged membrane(s) are detected at step 104. Maintenance of the electrolyzer may be initiated at step 108. Step 108 may entail causing any suitable action to be performed for initiating the maintenance, including, but not limited to, inventory consultation, operators shift assignment and equipment preparation or calibration.

At step 110, one or more first tests (referred to herein as confirmatory tests) are performed in the electrolyzer to validate the outcome of step 104. Although step 110 is illustrated as being performed after steps 106 and 108 it should be understood that, in some embodiments, step 110 may be performed immediately after step 104. According to one embodiment, a helium leak test is performed at step 110 to confirm the presence of damaged membranes identified at step 104. In one embodiment, at least one of the first (or confirmatory) test(s) is based on an injection of inert gases at an anode and at a cathode of each cell of the electrolyzer. In other alternative embodiments, the second and/or third detection methods described above may be carried out to perform the confirmatory test(s) at step 110. Once the confirmatory test(s) are performed, an assessment is made at step 110 to determine whether the confirmatory test(s) confirm the presence of damaged membrane(s). If at least one of the test(s) performed at step 110 confirms the presence of at least one damaged membrane, the next step 112 may be to cause replacement of the damaged membrane(s). Step 112 may comprise causing disassembling/assembling activities to be performed to replace the at least one damaged membrane.

At step 114, a second test (referred to herein as an inert gas (e.g., helium) leak test) is executed in the electrolyzer to detect any damaged membranes. In some embodiments, step 114 may be performed after the replacement activities of step 112. These replacement activities may cause membrane damages due, for instance, to mechanical tensions, torsions, and the like. In other embodiments, step 114 may be performed to confirm the outcomes of the confirmatory test(s) performed at step 110, after it has been determined at step 110 that the confirmatory test(s) failed to confirm the presence of damaged membrane(s) and no replacement activities were performed at step 112. In some embodiments, the confirmatory test(s) of step 110 may fail to confirm the presence of damaged membrane(s) by producing a false negative, for instance due to mishandling or bad manipulation of the electrolyzer or components thereof. In this case, it may be desirable to execute the inert gas test at step 114, as a redundant step.

A subsequent assessment is then performed at step 116, to re-assess whether one or more damaged membranes have been detected following step 114 (i.e. based on an outcome of the inert gas test). If at least one damaged membrane is confirmed at step 116, the operation of the electrolyzer is caused to stop at step 118 and may be followed by the iteration of steps 110 to 116 until no damaged membranes are detected. In some embodiments, step 118 may comprise causing the operation of the electrolyzer to stop by interrupting an electrolyzer start sequence or blocking an electrolyzer start command, for instance the electrolyzer start of step 120. Otherwise, if no damaged membrane is detected at step 116, the next step 120 is to cause the electrolyzer to start, for instance by causing the electrolyzer power supply to be turned on.

At step 122, voltage measurements (referred to herein as “second voltage measurements”) are obtained in real-time or pseudo real-time at each operating cell of the electrolyzer, during load increase (i.e. during the main current rectifier ramp up, which occurs during the startup of the electrolyzer). The voltage measurements may be obtained using the one or more data acquisition devices (e.g., DAT modules 301) described herein above with reference to step 102. At step 124, data (i.e. voltage measurements) obtained at step 122 is analyzed to classify and detect operating cells with damaged membranes. In particular, a second classification of the plurality of cells into a first category of cells with a damaged membrane and a second category of cells without the damaged membrane is performed at step 124, based on the one or more second voltage measurements obtained at step 122. As will be described further below with reference to FIGS. 5C and 5D, in one embodiment, the step 124 of classifying and detecting damaged membrane(s) (during the electrolyzer's startup operation mode) is based on the approximation of the electrolyzer's single cell current efficiency, using a theoretical look up table in which each current efficiency range is associated with the time when each cell starts to produce chlorine according to the feeding current. Step 124 may be performed using any suitable computing device, such as the cell classification and damage detection module 303 described above with reference to step 104.

The method 100 may then perform an assessment at step 126 of whether damaged membrane(s) are detected. If this is the case and one or more damaged membranes are detected ate step 126, an alarm may be triggered similarly to step 106 described above. The electrolyzer is then caused to stop at step 128 and steps 112 to 126 may be repeated until no damaged membranes are detected. When it is determined at step 126 that no damaged membrane(s) are detected, the next step 130 is to proceed with normal electrolyzer operation.

Referring now to FIG. 2A, an embodiment of a system 200 for performing a Helium Leak Test, such as at step 110 and/or step 114 of FIG. 1A, will now be described. As described above, the Helium Leak Test may be performed using the system 200 to confirm the presence of damaged membranes in a chlor alkali electrolyzer, for instance in chlor alkali electrolytic cell 201. One or more components of the system 200 may be controlled (e.g., using any suitable computing device, not shown) to cause the execution of the Helium Leak Test. For example, injection of inert gases into the cell 201 may be controlled via a computing device (e.g., a computer-implemented controller).

In the illustrated embodiment, the cell 201 comprises a catholyte chamber 202, an anolyte chamber 204, and a membrane 206 separating the catholyte chamber 202 from the anolyte chamber 204. The cell 201 may be provided with a catholyte inlet 208 and an anolyte inlet 210 for injecting inert gases into the catholyte chamber 202 and the anolyte chamber 204, respectively. The inert gases may be injected when the cell 201 is emptied of any electrolytes, for instance during operations modes including, but not limited, to electrolyzer startup, filling, or heating up. The catholyte inlet 208 may be provided at the catholyte chamber 202 at a first position, and the anolyte inlet 210 may be provided at the anolyte chamber 204 at a second position different from the first position.

The cell 201 may be further provided with a catholyte outlet header 212 and an anolyte outlet header 214 for injecting inert gases into the catholyte chamber 202 and the anolyte chamber 204, respectively, and/or analyzing the concentration of inert gases therein. The catholyte outlet header 212 may be provided at the catholyte chamber 202, at a third position different from the first and the second positions, while the anolyte outlet header 214 may be provided at the anolyte chamber 204, at a fourth position different from the first, second and third positions. In other words, inert gas may be injected either via the inlets 208 and 210 or, in some instances, via the outlet headers 212 and 214, into their corresponding chambers 202 and 204. In particular, in one embodiment, inert gas may be injected into the cell 201 via the inlets 208, 210 when the electrolyzer is empty from fluids, and via the outlets headers 212, 214 when fluids are present in the electrolyzer.

A test module 216 may be provided for analyzing the concentration of inert gas mixtures in the cell 201. The test module 216 may be communicatively coupled to any part of the cell 210 via a communication link 218, for instance to the anolyte outlet header 214. The test module 216 may comprise, for instance, a device for analyzing the concentration of inert gas mixtures. At least one sensor (not shown) may be provided with the test module 216 for measuring the concentration of inert gases. In some embodiments, the communication link 218 may comprise at least one communications cable, for instance at least one coaxial cable, twisted pair cable, or fiber optic cable, among other possibilities. The test module 216 may comprise and/or may be controlled via any suitable computing device.

In one embodiment as shown in FIG. 2A, the catholyte inlet 208 may be used to inject a first inert gas 220₁ into the catholyte chamber 202, while the anolyte inlet 210 may be used to inject a second inert gas 220₂ different from the first inert gas 220₁ into the anolyte chamber 204. In one embodiment, the second gas 220₂ may be injected simultaneously with the first gas 220₁. In one embodiment, the first gas 220₁ is helium and the second gas 220₂ is nitrogen. The flow of the nitrogen gas 220₂ will mix and disperse leaked helium 222 through the membrane 206 to the anolyte outlet header 214 where the helium/nitrogen mixture concentration is analyzed by the test module 216. According to one embodiment, if helium concentration is above a pre-defined or pre-determined limit, also referred to herein as a “concentration threshold”, (for instance 0.01% v/v), then the membrane 206 is estimated to be damaged and should be replaced. In an alternative embodiment where non-chlor alkali electrolysis cells are tested, different pre-defined limits for helium concentration may be used. In some embodiments, other inert gases, for instance CO₂, may be injected if non-chlor alkali electrolysis cells including, but not limited to, hydrochloric acid electrolysis cells, non-alkaline water electrolysis cells, or fuel cells, are tested using the system 200. Thus, although reference is made herein to the cell 201 being a chlor alkali electrolytic cell, it should be understood that non-chlor alkali electrolysis cells may also apply.

According to an alternative embodiment, when electrolytic fluids (not shown) are present in the catholyte chamber 202 and the anolyte chamber 204 of the cell 201 (i.e. the cell 201 is at least partly filled with fluid), the cell 201 may be divided into a fluid-filled portion 224 and an empty portion 226 (i.e. a portion of the cell 201 empty of any fluid). Since fluids are present in the electrolyzer, helium gas 228 may be injected into the empty portion 226 of the catholyte chamber 202 via the catholyte outlet header 212 rather than via the catholyte inlet 208, and nitrogen gas 230 may be injected into the empty portion 226 of the anolyte chamber 204 via the anolyte outlet header 214 rather than via the anolyte inlet 210 to mix and disperse the leaked helium through the cell membrane 206. Membrane damage in the empty portion 226 of cell 201 may thus be detected (e.g., using test module 216) when the concentration of the inert gas in the gas mixture at the anolyte outlet header 214 is above the pre-determined limit.

With continuous monitoring of the helium gas concentration at the anolyte outlet header 214, while the anolyte chamber 204 and the catholyte chamber 202 of the cell 201 are filled, the position of membrane damages can be determined. It also becomes possible to calculate the manner in which, in operation, the concentration of hydrogen in chlorine will increase with the decreasing fluid levels in the cell, when the current of the cell is increased and the foam zone at the top of the cell also increases.

According to a preferred embodiment, the inert gas test is conducted in an assembly of many electrolysis cells where the flow of the first inert gas 220₁ is lower than the flow of the second inert gas 220₂. The time it takes the concentration rate of change of the inert gas mixture to exceed the pre-determined limit (i.e., a concentration rate of change threshold) defines which electrolysis component in the assembly has severe damage.

FIG. 2B illustrates a plot 240 of the helium gas concentration at the anolyte outlet header 214 over time, since the start of the injection of helium gas 228 at the catholyte outlet header 212 provided at the catholyte chamber 202. As can be seen from plot 240, multiple step changes (as in 242 and 244) in the increase in helium gas concentration can occur. In one embodiment, the test module 216 may be configured to trigger the alarm indicative of detection of damaged membrane(s) if a step change greater than 0.01% v/v is detected. If no step change is detected (i.e. the increase in helium gas concentration is continuous), the test module 216 determines that no severely damaged membrane is present in the electrolyzer. In the example illustrated in plot 240, an alarm is triggered upon detection of step changes 242 and 244, which are both above the limit of 0.01% v/v. The position of a damaged cell can then be determined (e.g., using the test module 216) based on the time taken by the concentration rate of change of the inert gas mixture to reach the pre-determined limit. Continuing with the example illustrated in FIG. 2B, the faster it takes the inert gas mixture to reach the step change 242, the closer the damaged component is to the test module 216. The longer it takes the mixture to reach the step change 244, the farther the damaged components are from the test module 216. Other embodiments may apply.

Referring now to FIG. 3, an embodiment for an electrolysis cell voltage measurement and classification system 300, will now be described. The system 300 may be used to perform steps 102, 104, 122, and 124 of the method 100 described above with reference to FIGS. 1A and 1B. The system 300 comprises DAT modules 301 that measure differential cell voltages of an electrolyzer 304. The DAT modules 301 are configured to measure the differential cell voltages from cathode to cathode or anode to anode in the electrolyzer 304, with a given accuracy, such as +/−1 millivolt or any other suitable precision level. In one embodiment, the electrolyzer 304 may comprise an industrial chlor-alkali electrolyzer comprising a plurality of cells (not shown). In one embodiment, the cells may be provided in a series configuration, parallel configuration, or a combination thereof. In some embodiments, the electrolyzer 304 comprises up to 160 cells. Other embodiments may apply. Protected metal wires 305 may be used to connect the inputs of each DAT module 301 to terminals of the cathodes or anodes in adjacent cells of the electrolyzer 304. In some embodiments, each DAT module 301 may measure up to 32 voltage inputs associated with a given cell of the electrolyzer 304. The DAT modules 301 may each comprise a plurality of components, for instance analog to digital converters, digital filters, memory buffers and/or microcontrollers to execute data acquisition and transmission routines, among other possibilities.

Data measured by the DAT modules 301 may be transmitted, using a transmission link 306, to a data processing and communication module 302 which obtains, as per steps 102 and 122 of FIGS. 1A and 1B, the voltage measurements acquired by the DAT modules 301. For purposes of illustration, the transmission link 306 is depicted in FIG. 3 as a wired connection between the DAT modules 301 and the data processing and communication module 302. However, it should be understood that communication between the DAT modules 301 and the data processing and communication module 302 may occur across wired, wireless, or a combination of wired and wireless networks. In one embodiment, the wireless network may comprise a Personal Area Network (PAN), Local Area Network (LAN), Wireless Local Area Network (WLAN), Metropolitan Area Network (MAN), Wide Area Network (WAN), or combinations thereof. The transmission link 306 may include any number of networking devices such as routers, modems, gateways, bridges, hubs, switches, and/or repeaters, among other possibilities, communicatively coupled to the DAT modules 301 and the data processing and communication module 302 at any point along the network. In some embodiments, the transmission link 306 may be implemented using wireless broadcasting, wherein at least one transmitter, for instance at least one of the DAT modules 301, may transmit data to at least one receiver, for instance the data processing and communication module 302 via at least one antenna provided with the at least one transmitter and/or the at least one receiver. In other embodiments, the transmission link 306 may comprise at least one communications cable, for instance coaxial cable, twisted pair cable, or fiber optic cable, among other possibilities.

The data processing and communication module 302 may process data received from the DAT modules 301 and transmit the data to a cell classification and damage detection module 303. In some embodiments, the data processing and communication module 302 may be communicatively coupled to a shutdown relay 308, for instance the shutdown relay 308 of an electrolysis plant wherein the electrolyzer 304 is operating. The data processing and communication module 302 may execute and send emergency stop signals 307 to the shutdown relay 308. The shutdown relay 308 may be communicatively coupled to a plant Supervisory Control and Data Acquisition (SCADA) system (not shown). When actuated, the shutdown relay 308 may be used to initiate a shutdown of the electrolyzer 304. In some embodiments, the cell classification and damage detection module 303 may be remote from the location of the electrolyzer 304, DAT modules 301, data processing and communication module 302 and/or shutdown relay 308. In some embodiments, the cell classification and damage detection module 303 may comprise a cloud server. In addition, it should be understood that, although illustrated as separate components, the data processing and communication module 302 and the cell classification and damage detection module 303 may be combined or integrated into a single component.

The data processing and communication module 302 may receive, from the DAT modules 301, a transformer rectifier shunt current measurement using, for example, a 4-20 mA converter terminal (not shown) provided at the data processing and communication module 302. The data processing and communication module 302 may broadcast voltage and current data streams sampled at a given rate, for example one point per second, to the cell classification and damage detection module 303. In some embodiments, the cell classification and damage detection module 303 may receive from a third-party module 310 (such as a computer server), sometimes referred to as a Distributed Control System or DCS, electrolysis process measurements including, but not limited to, catholyte outlet temperature, caustic outlet concentration, and inlet and/or outlet pH. According to one embodiment, the cell classification and damage detection module 303 may then be configured to classify electrolysis cells and detect damaged membrane(s) from the voltage measurements (and, optionally, the data received from the third-party module 310), as per steps 104 and 124 of FIGS. 1A and 1B.

With reference to FIG. 4, a schematic diagram of an example computing device 400 is illustrated. The computing device 400 may be used to implement the method 100 described above with reference to FIGS. 1A and 1B and/or one or more elements of the system 300 described above with reference to FIG. 3, including part or all of the data processing and communication module 302 and/or part or all of the cell classification and damage detection module 303. As depicted, computing device 400 includes at least one processor 402, a memory 404 storing instructions 406, and at least one input/output (I/O) interface (illustrated as ‘Inputs’ and ‘Outputs’). For simplicity only one computing device 400 is shown but system may include more computing devices 400 operable by users to access remote network resources and exchange data. The computing devices 400 may be the same or different types of devices. The elements of the computing device 400 may be connected in various ways including directly coupled, indirectly coupled via a network, and distributed over a wide geographic area and connected via a network (which may be referred to as “cloud computing”).

Each processor 402 may be, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), or any combination thereof.

Memory 404 may include a suitable combination of any type of computer memory that is located either internally or externally such as, for example, random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

The I/O interface enables the computing device 400 to interconnect with one or more input devices, such as a keyboard, mouse, camera, touch screen and a microphone, or with one or more output devices such as a display screen and a speaker.

In some embodiments, the computing device 400 includes one or more network interfaces to enable the computing device 400 to communicate with other components, to exchange data with other components, to access and connect to network resources, to serve applications, and perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optics, satellite, mobile, wireless (e.g. Wi-Fi, WiMAX), SS7 signaling network, fixed line, local area network, wide area network, and others, including any combination of these.

Referring now to FIGS. 5A, 5B, 5C and 5D, electrolyzer cell voltage and current profiles will now be described, in accordance with one embodiment. The cell voltage and current profiles are illustrated when a membrane is failing during electrolyzer shutdown (FIGS. 5A and 5B), and when a membrane is failing during electrolyzer startup (FIGS. 5C and 5D).

As can be seen from FIGS. 5A and 5B, an electrolyzer shutdown occurs when the electrolyzer's rectifier current 502 decreases from normal operation load (labelled as I_normal in FIG. 5A) to zero (0) kiloamperes. A voltage of a chlor alkali electrolyzer cell that has a damaged membrane may drop rapidly (as illustrated by curve 504 of FIG. 5B) compared to non-damaged membranes, where the voltage (illustrated by curves 504′, 504″) may stay at a level greater than water electrolysis thresholds during the polarization period (after main current rectifier cutoff). According to one embodiment, a classification of the monitored cells into those with damaged membranes and those with non-damaged membranes may be performed using the systems and methods described herein (e.g., at step 104 of FIG. 1A), during the electrolyzer shutdown operation mode (as described above). According to one embodiment for chlor alkali electrolysis, the classification of membrane failure severity is based on the automatic calculation of the current efficiency of each membrane during the shutdown period. A formula used to perform this calculation has the form of:

CE ⁢ % = f ⁡ ( Δ ⁢ t ) ( 1 )

• • Where:
  • CE %: Membrane Current Efficiency for each cell composing the electrolyzer;
  • Δt: Time 506 (of FIG. 5B) that the cell voltage takes to switch from chlorine electrolysis to water electrolysis, for instance at 1.9 volts;
  • f: parametrical non-linear function defined using numerical simulation or laboratory data according to electrolyzer design or technology prior to deployment on production site.

According to one embodiment, by applying equation (1) to compute the current efficiency for each cell of the electrolyzer during the shutdown, classification of membrane status may be automatically performed at step 104 of method 100 described above with reference to FIGS. 1A and 1B.

FIGS. 5C and 5D show single cell voltage and current profiles when a membrane is failing during electrolyzer startup. As illustrated in FIG. 5C, an electrolyzer startup operation mode occurs when the electrolyzer is energized with a rectifier current load (as illustrated by curve 508 in FIG. 5C), where the current is increased from zero kiloamperes to a normal operation range. A single voltage (illustrated by curve 510 in FIG. 5D) of a chlor alkali electrolyzer cell that has a damaged membrane may take a much longer time 512 to reach voltage equilibrium level (labelled as V_equilibrium in FIG. 5D) (for instance 2.2 volts) for chlorine electrolysis compared to a non-failing cell membrane where the voltage (illustrated by curve 510′ in FIG. 5D) may reach the equilibrium level faster. According to one embodiment for chlor alkali electrolysis, the automatic classification of membrane failure severity (e.g., as performed at step 124) may be based on the automatic approximation of the current efficiency for each membrane during the startup period. In one embodiment, single cell current efficiency for each membrane may be determined from a theoretical look up table where, for each current efficiency range, a corresponding time is provided when each cell starts to produce chlorine according to the feeding current. This table is built based on the theoretical approximation of the produced chlorine versus time during electrolyzer startup according to the cell design and technology. At step 122 of FIG. 1B, current efficiency for each cell is determined using a correspondence of the time between the energizing of the electrolyzer by the rectifier current and reaching the chlorine electrolysis equilibrium voltage level (for instance 2.2 volts). The cells that have a current efficiency below a predefined threshold may be estimated as operating with damaged membranes.

Various aspects of the methods and systems described herein may be used alone, in combination, or in a variety of arrangements not specifically disclosed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects in one embodiment may be combined in any manner with aspects described in other embodiments. Although particular embodiments have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects. The scope of the following claims should not be limited by the embodiments set forth in the examples, but should be given the broadest reasonable interpretation consistent with the description as a whole.