US20150021193A1 - Method and system for monitoring the functionality of electrolysis cells - Google Patents

Method and system for monitoring the functionality of electrolysis cells Download PDF

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US20150021193A1
US20150021193A1 US14/326,952 US201414326952A US2015021193A1 US 20150021193 A1 US20150021193 A1 US 20150021193A1 US 201414326952 A US201414326952 A US 201414326952A US 2015021193 A1 US2015021193 A1 US 2015021193A1
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voltage
electrolysis
current
electrolysis cells
cell
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Inventor
Florian Verfuß
Jakob Jörissen
Gregor Polcyn
Gabriel Toepell
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Covestro Deutschland AG
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Bayer MaterialScience AG
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/14—Alkali metal compounds
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
    • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/02—Process control or regulation
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/70—Assemblies comprising two or more cells
    • C25B9/73—Assemblies comprising two or more cells of the filter-press type
    • C25B9/77—Assemblies comprising two or more cells of the filter-press type having diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04544—Voltage
    • H01M8/04552—Voltage of the individual fuel cell
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04574—Current
    • H01M8/04582—Current of the individual fuel cell
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04664—Failure or abnormal function
    • H01M8/04671—Failure or abnormal function of the individual fuel cell
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the invention relates to a method for monitoring the functionality of electrolysis cells. Furthermore, the invention relates to a system for monitoring the functionality of electrolysis cells and in particular the use thereof in chlor-alkali electrolysis.
  • the invention is directed to monitoring methods known per se for electrolysis cells, which conventionally make use of the detection of an averaged current-voltage characteristic of the cell.
  • the monitoring of electrolysis facilities and the diagnosis of defective cells are fundamentally based on the measurement of process-relevant parameters such as temperatures, differential pressures, or also gas concentrations, but above all on the measurement of cell voltages and cell current.
  • the cell voltage is very sensitive with respect to changes in the electrolyzes and is easily detectable, also at the individual cells.
  • Outotec describes, in WO 2005/052700 A1, a monitoring system for copper electrolysis.
  • the data of typically several hundred single cells, distributed onto multiple so-called stacks, are processed.
  • it consists of a plurality of modules which communicate with one another, and which assume different data (partial) processing steps (cf., for example, WO 2007/087728 A1, WO 2001/078164 A3).
  • the tasks of the modules disclosed therein can be described as follows:
  • the chronological change of the voltage is also permanently monitored and compared to a reference value of the permissible change k*di/dt.
  • Both systems analyze the measurement data only with respect to established limiting values. These can also be designed dynamically and can even be optimized on the basis of historical data and learning-capable structures, however, they do not permit the qualitative or quantitative determination of errors in individual electrodes.
  • a system is known from EP 00002006418 B1, which compares the single cell voltages to one another and assigns a degree of damage (not damaged, not severely damaged, severely damaged) via two limiting values.
  • the intention is above all for defects (so-called pinholes) on ion exchange membranes to be discovered. These are only detectable early when the NaCl electrolyzer is put into operation (i.e., at low current density), since the transfer of NaOH increases the pH value of the anolyte, and then the formation of oxygen is preferred.
  • This runs at a cell voltage between 1.2 V and 1.5 V and is therefore approximately one volt less than the voltage for chlorine formation (in combination with hydrogen-developing cathodes).
  • the chlorine formation With increasing current density, the chlorine formation supersedes the oxygen formation and the cell voltage jumps to the chlorine potential. If the voltage of a cell only increases slowly, however, a defect can be presumed. Inferences about the size and position (top or bottom half of the cell) can then be drawn by analyzing further measured variables such as differential pressure or fill level in the cell, or also by adapting a parameter model to the i-U curves (for small current densities, according to the patent figure up to approximately 0.5 kA/m 2 ).
  • the method according to WO 2001/078164 A2 permits finer damage classification.
  • the focal point here is the extraction and identification (pattern recognition) of events within the continuously recorded input data and the linkage thereof to diagnoses, which are stored in a databank.
  • Measured physical variables or also, as described as preferred in WO 2001/078164 A2 variables already calculated from measured values such as data from analyses in the time or frequency range or adaptation parameters from the regression of i-U curves, as are ascertained according to WO 2006/133562 A1, can be used as input data.
  • the diagnosis then runs in two steps:
  • the quality of the adaptation is checked. If there is a sufficient coefficient of determination and confidence interval, the ascertained adaptation parameters are stored in a databank and compared to reference parameters (for example, from cell ageing models) or assigned to so-called previously established “operation classes”. Every “operation class” applies for a specific parameter value range and characterizes a cell status.
  • reference parameters for example, from cell ageing models
  • operation classes Every “operation class” applies for a specific parameter value range and characterizes a cell status.
  • a similar parameter model is used according to DE 10217694 A1 for the dynamic determination of the i-U characteristic of a fuel cell having a motor as a consumer. Current and voltage are continuously recorded in the event of a load change and the adaptation parameters are determined, which can be used for the torque control and regulation of the drive.
  • a further approach for identifying anomalies is the use of predictive models, using which the normal operating state is calculated.
  • the deviation of the measured values from the normal, calculated state is now detected and defined as an anomaly.
  • the better data base is advantageous to represent the normal operating state; the difficulty of developing a good model which can image various operating states is shown to be disadvantageous.
  • WO 2005/052700 A1 explains the functionality of an online monitoring system for copper electrolysis.
  • the theoretical cell voltage is calculated as a function of other operating parameters such as temperature, current density, or concentration.
  • the deviation between measured and theoretical cell voltage is ascertained and the trend thereof is analyzed by means of a model.
  • this trend is converted into a status index (number between 0 and 1), which characterizes the instantaneous state of the cell.
  • a new condition index which characterizes the cell status over a longer period of time is then ascertained.
  • WO 2007/087729 A1 discloses a system and a method, respectively, to simulate the normal operation of a facility by means of predictive models and detect errors on the basis of the deviation between measured process parameters and the modeled normal operation.
  • a model is prepared and validated, or the validity range and the precision are determined, on the basis of reference data and expert knowledge for respectively one operating state (for example, putting into operation and taking out of operation, load change).
  • one operating state for example, putting into operation and taking out of operation, load change.
  • deviations which lie outside the precision can be identified later as an anomaly.
  • the model parameters deviations between model and measured values, which occur due to errors which are already known, can also be stored as a so-called signature or as an anomaly pattern (sequence of signatures) in a databank.
  • the process variables calculated using the respective model are then compared to the measured process variables and the signature thereof is calculated from the deviations. If the deviations of the signature are sufficiently large, an anomaly can be presumed. If the calculated signature then corresponds to a signature stored in the databank, the ascertainment of an error is possible.
  • the construction which is expressly described as an example, comprises the fuel-cell stack, an inverter, a control unit, a water metering system, and a load (motor).
  • a voltage having a harmonic wave is applied to the fuel cell by the inverter, which also results in ripple in the current at the output of the fuel cell.
  • the impedance of the fuel cell is determined If the value is excessively high, water is metered to the cells. For this purpose, only the voltage of one cell is measured as representative.
  • a rectangular harmonic wave having an amplitude in the mV range and a frequency of 8 kHz is typically applied via the controller of the inverter.
  • harmonic waves having arbitrary shape and arbitrary amplitudes and also frequencies can also be generated. These can be used for more extensive monitoring (for example, to infer the status of the cell components), also in conjunction with more complex analysis methods (Fourier transform).
  • the system is to be applicable to the monitoring of arbitrary current generators, but in particular fuel cells, which are coupled to an arbitrary current converter (an “AC/DC rectifier” is also listed as an example).
  • a reliable method for identifying faulty individual electrolysis cells from a plurality of electrolysis cells of an electrolyzer has heretofore not been known.
  • the object of the present invention proceeding from the above-described prior art, is to provide an improved monitoring method for electrolysis cells, in particular for use in chlor-alkali electrolysis, which overcomes the above disadvantages and allows reliable identification of electrolysis cells which are defective or impaired in their function from a plurality of electrolysis cells of an electrolyzer, in particular in the case of chlor-alkali electrolysis.
  • the subject of the invention is a method for monitoring the functionality of electrolysis cells of an electrolysis facility, in particular a membrane electrolysis facility, preferably of multiple electrolysis cells operated simultaneously in production, characterized in that the current/voltage curve of an AC voltage overlaid on the electrolysis voltage is measured and compared to the predefined characteristic values of a functional electrolysis cell and the comparison value is detected (see FIGS. 1 and 2 ).
  • the advantage and novelty of this monitoring system in relation to existing and commercially available systems is the acquisition of additional items of information about the electrochemical behavior by measuring current and voltage time curves with higher resolution than usual, in order to therefore use the harmonic waves in the current and voltage for the diagnosis of the cell status.
  • These items of information are not available in conventional systems, since their measured value detection at conventional sampling rates (at most 100 Hz) cannot sufficiently resolve the harmonic waves having basic frequencies of typically 300 Hz or 600 Hz (depending on the rectifier construction, 6 or 12 pulses).
  • the effort is made to obtain current and voltage signals which have as little interference and are as free of harmonic waves as possible using integrating elements and filters.
  • the systems can only access averaged values for current and voltage. It is therefore possible to register the change of the cell voltage over a longer operating time (drifting of the cell voltage) and possibly to diagnose errors by incorporating data of other sensors or chemical analyses. However, there is no access to an instantaneous current-voltage characteristic, which reacts particularly sensitively to damage and even allows the assignment of damage to individual cell components (for example, a pinhole in the membrane).
  • the measuring unit ( 8 in FIG. 1 ) must have a sufficient resolution both for the level of the electrical signal and also for the time (for example, for 100 measurement points per half wave of a 600 Hz harmonic wave from a 12 pulse rectifier, a sampling rate of 120 kHz results; the measurements during the development of the method were performed using a measuring card having 2 MHz sampling rate and 14 bit resolution).
  • the time curve of the current I ( 6 and 7 ) must always be detected simultaneously with the voltage measurement U ( 5 ) at the same resolution.
  • the signal from the shunt resistor 2 which is installed in the normal case in an electrolysis facility, (for example, voltage drop in the range of 50 mV at currents of approximately 15,000 A) indicates the mean value of the current strength I DC using integrating measuring instruments very precisely.
  • the signal from a shunt resistor 2 is unsuitable solely because of excessively large overlaid interference, however.
  • a sufficiently sensitive current measuring unit is required here, which also records the alternating current component I AC in the frequency range generated by the rectifier 1 with low phase and amplitude errors. It is preferably based on the induction by way of the magnetic field of the current, for example, as in a Rogowski coil 3 having a corresponding amplifier. This only detects the alternating current component (AC component I Ac ) of the current. The total current including the ripple can then be ascertained by addition of the AC component I Ac to the direct current component (DC component I DC ), which is generally accessible from the measurement on a shunt resistor 2 in the control room.
  • DC component I DC direct current component
  • the cell voltages U are to be detected as close as possible to the electrolyzer 4 ( 5 ) and transmitted therefrom in digital form to the control room.
  • the permissible voltage values within the bipolar switched electrolyzer and the potential difference in relation to earth are to be considered with respect to metrology and the safety regulations (for example, by potential-separated data transfer).
  • Voltage U ( 5 ) and current I ( 6 and 7 ) of the cells must be detected synchronously, wherein the current measuring unit is only required once in a circuit made of rectifier 1 and electrolyzer 4 .
  • EIS electrochemical impedance spectroscopy
  • the novel monitoring system for large-scale industrial electrolyzers not only uses an excitation signal which can be influenced, but rather it uses the existing ripple of the rectifier 1 , which in principle does not have a simple, precisely defined oscillation form.
  • the ripple depending on the rectifier construction (6 pulse or 12 pulse), consists of a frequency spectrum having a base frequency of 300 Hz or 600 Hz and the multiples of these base frequencies.
  • the amplitude is variable and is dependent on the rectifier operating point (i.e., on the fraction of the full load power). If this is not in the optimum range, for example, upon setting of smaller powers by phase angle control from a large rectifier, the ripple can greatly exceed the typical 5%.
  • This preparation unit can fundamentally be embodied in this case as a hardware or software solution.
  • (bandpass) filters are conceivable in this case, using which the current and voltage components in the rectifier base frequency may be isolated for analysis.
  • an averaging algorithm worked out for this purpose was used. It automatically recognizes the limits of the individual pulses in a current or voltage time curve, cuts apart the pulses, overlays them, and forms the average values from the respectively overlaid data points of all pulses.
  • the analysis unit 8 finally produces the relationship between the current and voltage harmonic waves and the state of the electrolysis cell.
  • the foundation of this analysis is formed by the relationship between the current and voltage harmonic wave amplitudes and the phase shift between both harmonic waves.
  • the simplest and most effective possibility for analyzing this is offered by plotting as a dynamic i-U curve for the detected small current density range, as shown in FIG. 2 (the current I is converted for this purpose into the current density i, i.e., in relation to the active surface of the electrolysis cell).
  • the curved profile then contains as cell-relevant items of information:
  • a first analysis step is the estimation of a complete i-U curve for the entire current density range from the data obtained for the small current density range. From this, the following may be differentiated:
  • the novel monitoring system can additionally also incorporate further analysis methods known in principle from the literature for finer analyses.
  • the items of information contained in the measurement results which go beyond the data detected in the existing and commercially available systems, can optimally utilize:
  • the novel method is preferably carried out in an electrolyzer, in which the electrolysis cells are provided having bipolar interconnection of the electrolysis cells.
  • the harmonic wave AC voltage of the rectifier is used as the AC voltage for the generation of the electrolysis voltage, for example, from a network AC voltage.
  • the possible interfering components in the AC voltage signal and/or alternating current signal are filtered out before or after the detection of the signal.
  • a preferred form of the novel method is advantageous, in which the alternating current/AC voltage components are measured at a sampling rate of at least 10 kHz, preferably at least 100 kHz.
  • the measurement of the alternating current component at the current supply to the electrolysis cell to be measured is performed inductively, in particular with use of a Rogowski coil.
  • the slope in a derived current density-voltage characteristic curve is used as a characteristic value for the functionality of the individual electrolysis cells (i-U curve).
  • the extrapolated axis section of the characteristic curve for the current density zero in a derived current density-voltage characteristic curve is used as a characteristic value for the functionality of the individual electrolysis cells.
  • the change of the hysteresis of the characteristic curve can be used in particular as a characteristic value for the functionality of the individual electrolysis cells in a derived current density-voltage characteristic curve.
  • a warning signal is generated, which is used for informing the operating personnel or for automatically taking the individual electrolysis cells or the entire electrolyzer out of operation.
  • the novel method is applied in particular in electrolysis facilities for electrolysis of alkali chloride solutions, in particular of lithium chloride, sodium chloride, or potassium chloride solutions, preferably of sodium chloride solutions or of hydrochloric acid.
  • alkali chloride solutions in particular of lithium chloride, sodium chloride, or potassium chloride solutions, preferably of sodium chloride solutions or of hydrochloric acid.
  • the novel method is not fundamentally restricted to these electrolysis methods.
  • Application in water electrolysis is also conceivable.
  • a further object of the invention is also a system for monitoring the functionality of electrolysis cells of an electrolysis facility having multiple electrolysis cells, in particular a membrane electrolysis facility, preferably having multiple electrolysis cells operated simultaneously in production, at least comprising a voltage generator for generating an AC voltage overlaid on the electrolysis DC voltage, a voltage measuring unit connected to measure the DC voltage component and the AC voltage component over the individual electrolysis cells, at least one current measuring unit for measuring the direct current component and the alternating current component of the electric current, which flows to the electrolysis cells, and a data processing unit, which records the measured values of the DC voltage components, the AC voltage components, the direct current component, and the alternating current component, generates a current/voltage curve and compares the current/voltage curve of the individual electrolysis cells to the predefined characteristic values of a functional electrolysis cell.
  • a monitoring system is preferred which has current and voltage measuring units for electrolysis cells in an electrolyzer having bipolar interconnection of the electrolysis cells.
  • a monitoring system is preferred in which the AC voltage generator is formed by a rectifier for generating the electrolysis voltage from AC voltage, which has a harmonic wave AC voltage in operation.
  • a novel monitoring system is particularly preferred which comprises electronic filters for possible interfering components in the AC voltage signal upstream of the detection unit of the data processing unit.
  • the current measuring unit of the monitoring system contains, in addition to the conventional direct current measurement with the aid of a shunt resistor as described above, in particular an inductive alternating current measuring unit and comprises in particular a Rogowski coil as a measured value sensor.
  • the data processing unit has an output unit having signal generator.
  • the signal generator is electrically connected to an optical and/or to an acoustic warning device and/or to a facility controller for the operation of the individual electrolysis cells or for the operation of selected cell stacks or for the operation of the entire electrolyzer.
  • the system is particularly preferably connected to an electrolysis facility for the electrolysis of alkali chloride solutions, in particular lithium chloride, sodium chloride, or potassium chloride solutions, preferably of sodium chloride solutions or hydrochloric acid.
  • alkali chloride solutions in particular lithium chloride, sodium chloride, or potassium chloride solutions, preferably of sodium chloride solutions or hydrochloric acid.
  • FIG. 1 shows a schematic diagram of the monitoring system according to the invention
  • FIG. 2 shows an example of the chronologically detected cell voltage U and current density i and the detail generated therefrom from the current density-voltage characteristic curve (i-U curve)
  • FIG. 3 shows a comparison of the i-U curves before and during membrane damage due to calcium addition
  • FIG. 5 shows a time curve of the membrane damage due to a pinhole: collapse of the cell voltage predominantly due to the axis section of the i-U curve (change of the electrochemical reaction) but hardly due to its current-dependent component (the slope b, i.e., the ohmic resistance, remains substantially constant)
  • the dynamic current-voltage characteristic of the single cells is analyzed for the monitoring. It results from the reaction of the cell 4 to the periodic alternating current signal, which is present as a harmonic wave of the direct current as a result of the ripple of the rectifier 1 in many industrial electrolysis facilities.
  • FIG. 1 shows the measurement construction in principle. Due to the ripple, the current I, with which the electrolysis cell 4 is supplied by the rectifier 1 , is not constant but rather oscillates periodically by a small amount. This minimal current change also has an effect on the electrolysis cell 4 , which reacts with periodic changes of the cell voltage U.
  • the idea of the measurement concept is that the time curve of both the current and also the cell voltage is detected and by comparison of the periodic changes of both dimensions, inferences can be drawn about the status of the cell and its components (see FIG. 2 ).
  • membrane damage was experimentally simulated: The goal of the experiments was to detect the fault of the functionality of a chlor-alkali electrolysis cell by way of the monitoring method according to the invention after intentional damage of the membrane:
  • a chlor-alkali laboratory cell anode: expanded metal dimensionally-stable anode (DSA), cathode: oxygen depolarized cathode (ODC), membrane: Flemion F 8020 Sp, finite gap arrangement
  • DSA expanded metal dimensionally-stable anode
  • ODC oxygen depolarized cathode
  • membrane Flemion F 8020 Sp, finite gap arrangement
  • the membrane damage was carried out as follows:
  • the membrane was pierced using a titanium wire and an approximately 0 5 mm hole (pinhole) was generated (beginning of the experiment identified in FIG. 5 ).
  • the wire had been installed in the rear side of the anode chamber together with a feed-through before the cell was put into operation. For the experiment, it could be moved up to the membrane from the outside without touching the DSA grating.
  • ripple measurements were carried out at intervals of 15 minutes (during the experiment even at significantly shorter intervals of up to 10 seconds), in that the ripple cell voltage U and the ripple cell current I (voltage drop at a shunt) were detected at sampling rates of 500 kHz via a measuring card connected to a computer.
  • the ripple i-U curves according to FIG. 2 were obtained, which were analyzed by means of linear regression.
  • Two ripple i-U curves are shown before and during calcium contamination as examples in FIG. 3 (the measurement times are plotted in FIG. 4 ).
  • the dashed straight line shows the linear regression of the curve.
  • the circles correspond to the mean values of the ripple cell voltage and of the ripple current density.
  • the prior art is heretofore the tracking of the time change of the cell voltage, which does indicate a malfunction, but does not permit further diagnosis.
  • the novel system provides additional items of information for diagnosis in the form of the time change of the axis section and of the current-dependent component of the ripple i-U curves.
  • the analyses result in the following:
  • the cell voltage increases continuously. It is known that calcium forms poorly-soluble deposits in the membrane and therefore obstructs the sodium ion transport, so that the membrane resistance increases. As a result, the current-dependent component increases simultaneously with the mean cell voltage, while the axis section remains constant.
  • Basic solution passes through the pinhole into the anode chamber, increases the pH value, whereby the anodic oxygen formation is preferred and the chlorine production comes to a stop, i.e., a strong change of the electrochemical reactions occurs. Since the oxygen formation occurs at lower equilibrium potential, the cell voltage decreases abruptly, as does the axis section. The current-dependent component remains nearly unchanged.

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  • Chemical Kinetics & Catalysis (AREA)
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US14/326,952 2013-07-17 2014-07-09 Method and system for monitoring the functionality of electrolysis cells Abandoned US20150021193A1 (en)

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DE102013213982.9A DE102013213982A1 (de) 2013-07-17 2013-07-17 Verfahren und System zur Überwachung der Funktionsfähigkeit von Elektrolysezellen
DE102013213982.9 2013-07-17

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EP (1) EP2826889B1 (de)
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US20170317366A1 (en) * 2016-04-27 2017-11-02 Hyundai Motor Company Pinhole determination method and system for fuel cell
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CN109507546A (zh) * 2018-11-06 2019-03-22 云南云铝涌鑫铝业有限公司 铝电解槽打壳气缸的检测电路和基于压差的绝缘检测方法
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