DE102011110507B4 - Method and system for determining the single element current yield in the electrolyser - Google Patents

Abstract

Method for determining the current yield of the individual elements of an electrolyzer comprising at least one cell element of an electrolyzer, characterized in thata. an electrolysis current I is applied to an electrolyzer consisting of at least one individual element and the electrolysis current I is increased to a certain current value IEND in the range of 1 kA and 2.7 kA,b. a point in time t0 is determined, which can be freely selectable before or after the electrolysis current is switched on, the electrolysis current not being allowed to exceed a certain maximum value I0 between 10 A and 200 A,c. the voltage Uides of at least one individual element is measured and the mean value of all individual element voltages UM is formed, i.e. the point in time tEND is determined after which all cell voltages Uid of the individual elements i deviate by a defined voltage difference ΔUEND from the mean value of all individual element voltages UM, with ΔUEND being between 10 mV and 200 mV,e. the area Aiunder the stress curve Ui(x) of each individual element i is determined by numerical integration over the variable x in the limits between x0= x(t0) and xEND= x(tEND):Ai=∫x0xENDUi(x)dxwhere the variable x stands for either the time t or the electrolysis current I; f. the area AM under the stress curve of the average of all individual elements UM (x) is determined via numerical integration over the variable x in the limits x(t0) and x(tEND):AM=∫x0xENDUM(x)dxwhere the variable x is also for either the time t or the electrolysis current I stands; g. the average electrolyzer current efficiency CEEL is determined, and i.e. the current yield CEijof each individual element i is calculated as a function of the electrolyzer current yield CEEL using an empirical function f, which includes the area ratio Ai/AM.

Description

The invention relates to a method for determining the current yield of at least one cell element of an electrolyzer.

The voltage U and the current yield CE of a cell element of an electrolyser are important variables in the context of electrolysis technology, since the current or energy consumption EV of the electrolyser depends on these physical variables, and precise knowledge of this is important for the economic operation of a technical electrolyser system.

For reasons of practical assessment, the energy consumption of an electrolyser is usually related to the mass of the product and is therefore specifically presented. According to Bergner, "Development status of alkali chloride electrolysis, part 2", Chemical Engineering Technology 66 (1994) No. 8, the directly proportional relationship between specific energy consumption and voltage can be calculated as follows for classic chlorine-alkaline electrolysis: $$\text{EV}=\text{U/}\left(\text{f}\times \text{CE}\right)\left[\text{kWh/t}\right]$$

F denotes a product-specific Faraday constant with the unit [t/kAh], which is formed via the quotient of the molar Faraday constant and the molar mass of the product, since the electrochemical formation of the product depends directly on the current strength and thus the charges used.

The second important proportionality factor is the current yield CE, which indicates the percentage ratio of practically formed product quantity _MP and theoretically possible product quantity _MT based on the charges used: $$\text{CE}=100\times {\text{M}}_{\text{P}}{\text{/M}}_{\text{T}}\left[\text{\%}\right]$$

The current yield is always less than 100% due to charge losses due to stray currents, thermodynamic side reactions or membrane damage, which causes product to be lost.

Since the energy consumption of an electrolyser is the decisive criterion for the economical operation of a technical electrolyser system, assuming a constant current yield of all individual cell elements, the relationship between current and cell or electrolyser voltage is sufficient for assessing economical operation. However, if the current yield CE is not constant, a cell element can only be assessed as precisely as possible for economic operation by determining and monitoring the specific energy consumption EV as a direct function of the current yield to be determined in parallel.

Unlike the voltage U, the current yield CE of each cell element cannot be measured directly. Rather, the actual product quantity of each cell element must be determined from practical analyzes in order to arrive at results that can be used to adequately determine the energy consumption. Cowell, Martin and Revill have reviewed the well-known empirical methods, which are based on cathodic or anode-side balancing of the product, in "A new improved method for the determination of sodium hydroxide current efficiency in membrane cells", Modern-Chlor-Alkali Technology Vol. 5, SCI London (1992), detailed.

According to Cowell, Martin and Revill, the best known method is the so-called "cathodic balance" or "direct caustic soda collection method". This requires the amount of lye to be circulated over a longer period of time in a closed circuit, in which the current load is precisely measured. The amount circulated in the circuit is kept constant and the amount of lye produced is continuously discharged, with the concentration and flow rate of the lye produced having to be measured exactly. The electricity yield is then determined via the ratio of the amount of caustic produced compared to the amount of caustic produced that is theoretically possible given the electricity load over the longer period mentioned. The disadvantage of this method is that it is limited to the entire system, the production volume of an individual electrolyser or individual cells cannot be determined in this way.

In addition to other indirect methods, Cowell, Martin and Revill present the "sulphate key" method, which has become established as the so-called "anodic balance".

With this method, the anolyte flow rate is determined via the sodium sulfate concentration in the brine and anolyte, i.e. before and after the reaction, since sulfate is not changed by the electrochemical reactions in the cell. The anolyte volume flow can be determined by forming the ratio of the sulphate amounts in the brine and anolyte and multiplying this by the brine volume flow, which is referred to as the “sulphate key”. The amount of product is then determined by comparing the components in the brine with the components formed in the anolyte and chlorine cell gas.

In detail, the following variables are required for the anodic balance: The electrolysis current I [n/a] The brine volume flow V [ ^m3 /h]

An analysis of the following gas fractions in the anodic product gas: chlorine y _Cl2 [%v/v] oxygen y _O2 [%v/v]

An analysis of the following mass-related concentrations in the brine (educt): sodium hydroxide _CNaOH [g/l] sodium sulfate _CNa2SO4 [g/l] sodium _CNa2CO3 [g/l] sodium chlorate _CNaClO3 [g/l] hydrochloric acid _CHCl [g/l]

An analysis of the following mass-related concentrations in the anolyte (product): sodium sulfate _C'Na2SO4 [g/l] sodium chlorate _C'NaClO3 [g/l] hypochlorite _C'HOCl [g/l] hydrochloric acid _C'HCl [g/l]

After analyzing the required concentration, the anolyte volume flow V̇' is first calculated via the ratio of the sulfate concentration in the inflow brine and outflow anolyte, i.e. the application of the "sulfate key": $${\dot{V}}^{\text{'}}=\dot{V}\frac{C_{Na2SO4}}{C_{Na2SO4}^{\text{'}}}$$

$${\eta }_{HOCl}=\frac{C_{HOCl}^{\text{'}}\cdot {\dot{V}}^{\text{'}}}{n\cdot I\cdot \mathrm{0,980}}\cdot 100\text{\%}$$

$${\eta }_{HCl}=\frac{C_{HCl}\cdot \dot{V}-C_{HCl}^{\text{'}}\cdot {\dot{V}}^{\text{'}}}{n\cdot I\cdot \mathrm{1,36}}\cdot 100\text{\%}$$

$${\eta }_{Alkali}=\frac{C_{NaOH}\cdot \dot{V}}{n\cdot I\cdot \mathrm{1,4923}}\cdot 100\text{\%}$$

$${\eta }_{Na2CO3}=\frac{C_{Na2CO3}\cdot \dot{V}}{n\cdot I\cdot \mathrm{1,978}}\cdot 100\text{\%}$$

$${\eta }_{O_2}=\frac{2y_{O_2}}{y_{C{l}_2}+2y_{O_2}}\cdot \left(100-{\eta }_{NaCl{O}_3}-{\eta }_{HOCl}\right)\text{\%}$$

In the next step, the yields of the different anolyte components are calculated: $$n_{Na\mathrm{<figure-callout\; id="3"\; label="C\; l\; O"\; filenames="DE102011110507B4\_0040.png"\; state="\{\{state\}\}">C</figure-callout>}lO3}=\frac{C_{NaClO3}^{\text{'}}\cdot {\dot{V}}^{\text{'}}-C_{Na\mathrm{<figure-callout\; id="3"\; label="C\; l\; O"\; filenames="DE102011110507B4\_0040.png"\; state="\{\{state\}\}">C</figure-callout>}lO3}\cdot \dot{V}}{n\cdot I\cdot 0.662}\cdot 100\text{\%}$$

$$n_{HOCl}=\frac{C_{HOCl}^{\text{'}}\cdot {\dot{V}}^{\text{'}}}{n\cdot I\cdot 0.980}\cdot 100\text{\%}$$

$$n_{HCl}=\frac{C_{HCl}\cdot \dot{V}-C_{HCl}^{\text{'}}\cdot {\dot{V}}^{\text{'}}}{n\cdot I\cdot 1.36}\cdot 100\text{\%}$$

$$n_{Alkali}=\frac{C_{NaOH}\cdot \dot{V}}{n\cdot I\cdot 1.4923}\cdot 100\text{\%}$$

$$n_{Na2\mathrm{<figure-callout\; id="3"\; label="C\; O"\; filenames="DE102011110507B4\_0040.png"\; state="\{\{state\}\}">C</figure-callout>}O3}=\frac{C_{Na2\mathrm{<figure-callout\; id="3"\; label="C\; O"\; filenames="DE102011110507B4\_0040.png"\; state="\{\{state\}\}">C</figure-callout>}O3}\cdot \dot{V}}{n\cdot I\cdot 1.978}\cdot 100\text{\%}$$

$$n_{O_2}=\frac{2y_{O_2}}{y_{\mathrm{<figure-callout\; id="2"\; label="C\; l"\; filenames="DE102011110507B4\_0036.png,DE102011110507B4\_0040.png"\; state="\{\{state\}\}">C</figure-callout>}{l}_{}{}_2}+2y_{O_2}}\cdot \left(100-n_{NaCl{O}_3}-n_{HOCl}\right)\text{\%}$$

Finally, the current yield CE can be summed up using the individual current yields calculated in Equations (4) to (9): $$C{E}_{EL}=100\%-{\mathrm{<figure-callout\; id="2"\; label="n\; O"\; filenames="DE102011110507B4\_0036.png,DE102011110507B4\_0040.png"\; state="\{\{state\}\}">n</figure-callout>}}_O-n_{Na\mathrm{<figure-callout\; id="3"\; label="C\; l\; O"\; filenames="DE102011110507B4\_0040.png"\; state="\{\{state\}\}">C</figure-callout>}lO3}-n_{HOCl}-n_{HCl}+n_{Na2\mathrm{<figure-callout\; id="3"\; label="C\; O"\; filenames="DE102011110507B4\_0040.png"\; state="\{\{state\}\}">C</figure-callout>}O3}+n_{Alkali}$$

Compared to the cathodic balance, the anodic balance offers the advantage that the current yield can be determined analytically by taking samples of brine, anolyte and chlorine gas from individual cells. A disadvantage is the outlay on equipment required to determine the current yield of individual elements in the form of additional sampling points and time-consuming analyzes that tie up personnel.

Recently, a simplified anodic balance was developed using an empirical approach to minimize the analysis effort. Accordingly, an evaluation has shown that the current yield after the anodic balance essentially depends on two variables, the oxygen content in the product gas y _O2 and the hydrochloric acid volume flow in the inflow brine Q _A . Taking into account the density d _A and the mass concentration of the hydrochloric acid c _A , the following approximate formula is derived, with P1, P2 and P3 being constants to be determined empirically: $$\text{CE}=\text{<figure-callout id="1" label="P" filenames="DE102011110507B4\_0039.png,DE102011110507B4\_0040.png" state="{{state}}">P</figure-callout>}1-\left(\text{P2/I}\right)\times \left({\text{Q}}_{\text{A}}\times {\text{i.e}}_{\text{A}}\times {\text{c}}_{\text{A}}\right)+\left(0.5-{\text{y}}_{\text{O2}}\right)\times \text{<figure-callout id="3" label="P" filenames="DE102011110507B4\_0040.png" state="{{state}}">P</figure-callout>}3$$

• Wie in 1 dargestellt ist, erfolgt die anodische Chlorbildung bei einem Standardpotential von 1,36V bei 25 °C gegen Normalwasserstoffelektrode, während die kathodische Wasserstoffbildung ein Standardpotential von -0,83V bei 25 °C aufweist. Die thermodynamische Zersetzungsspannung - also die Differenz beider Potentiale - beträgt somit theoretisch 2,19V. Die anodische Sauerstoffbildung ist thermodynamisch sogar günstiger, da das Standardpotential selbst im sauren pH Bereich nur maximal 1,23V bei 25 °C beträgt. In der Praxis wird daher eine anodische Edelmetallbeschichtung auf der Anode aufgebracht, um die Überspannung für die Sauerstoffbildung zu erhöhen und damit die Chlorbildung zu begünstigen. Dieser Sachverhalt ist in 2 dargestellt, welche die resultierenden Potentialverläufe der Chlor- und Sauerstoffbildung an entsprechend beschichteten Anoden zeigt. Die Sauerstoffbildung hängt aber stark vom pH-Wert im Anolyt ab, wie in 3 illustriert wird. Bei niedriger Zellen-Stromausbeute, d. h. wenn größere Mengen von OH^--Ionen beispielsweise durch Membranlöcher in den Anodenraum gelangen, steigt der pH-Wert und das Potential der Sauerstoffbildung wird zu kleineren Werten verschoben. Damit wird die Sauerstoffbildung bei geringen Strömen wieder begünstigt und die resultierende Potentialdifferenz und damit Elementspannung ist niedriger als bei der anodischen Chlorbildung. Je mehr OH^--Ionen also in den Anodenraum eindringen, umso niedriger das Anodenpotential und damit die resultierende Zellspannung. Wird allerdings der Elektrolysestrom soweit erhöht, dass das Chlorbildungspotential überschritten wird, so ist die Chlorbildung wiederum die thermodynamisch günstigere Reaktion. Die zunehmende Turbulenz durch entstehende Chlor-Gasblasen führt außerdem dazu, dass die geringe Menge der in den Anodenraum eindringenden OH^--Ionen von der Anodenoberfläche entfernt und unter Hypochloritbildung neutralisiert werden. Mit zunehmendem Elektrolysestrom ist damit der Anteil der Sauerstoffbildung so gering, das nur noch das Chlorpotential maßgeblich zum anodischen Potential und zur Elementspannung beiträgt. Merkliche Unterschiede zwischen den Elementen in Form der Elektrolysespannung, die durch eindringende Lauge und nachfolgende Sauerstoffbildung beeinflusst wird, und damit auch in der Stromausbeute lassen sich somit nur bei niedrigen Elektrolyseströmen bis etwa 2,2kA beobachten.

In addition to the cathodic balance and the variants of the anodic balance, there are various approaches to replacing the indirect analysis methods for determining the current yield with direct - so-called online measuring methods such as voltage measurement. These methods make use of the following electrochemical relationship:

• As in 1 is shown, the anodic chlorine formation takes place at a standard potential of 1.36 V at 25 °C against standard hydrogen electrode, while the cathodic hydrogen formation has a standard potential of -0.83 V at 25 °C. The thermodynamic decomposition voltage - i.e. the difference between the two potentials - is therefore theoretically 2.19V. The anodic oxygen formation is thermodynamically even more favorable, since the standard potential even in the acidic pH range is only a maximum of 1.23V at 25 °C. In practice, therefore, an anodic noble metal coating is applied to the anode in order to increase the overvoltage for oxygen formation and thus promote chlorine formation. This situation is in 2 shown, which shows the resulting potential curves of chlorine and oxygen formation on correspondingly coated anodes. However, the formation of oxygen depends strongly on the pH value in the anolyte, as in 3 is illustrated. If the cell current yield is low, ie if large amounts of OH ^- ions get into the anode space through holes in the membrane, for example, the pH value increases and the potential for oxygen formation is shifted to lower values. This promotes the formation of oxygen again at low currents and the resulting potential difference and thus element voltage is lower than with anodic chlorine formation. The more OH ^- ions penetrate into the anode space, the lower the anode potential and thus the resulting cell voltage. However, if the electrolysis current is increased to such an extent that the chlorine formation potential is exceeded, then chlorine formation is again the thermodynamically more favorable reaction. The increasing turbulence caused by chlorine gas bubbles also means that the small amount of OH ^- ions penetrating the anode space are removed from the anode surface and neutralized with the formation of hypochlorite. As the electrolysis current increases, the proportion of oxygen formation is so low that only the chlorine potential makes a significant contribution to the anodic potential and element voltage. Significant differences between the elements in the form of the electrolysis voltage, which is influenced by the penetrating alkali and the subsequent formation of oxygen, and thus also in the current yield, can only be observed at low electrolysis currents of up to around 2.2 kA.

This effect can initially be used qualitatively in order to detect elements with membrane damage when starting up an electrolysis system by examining the voltage behavior of the individual elements is monitored. If the voltage is significantly lower when the load of the electrolysis current is initially increased to a certain level in the range of 1-2 kA, then the entry of considerable amounts of OH ^- ions into the anode compartment due to membrane damage can be proven. This method has been state of the art for a long time and has been used by Traini, Mojana and Gusmini in U.S. 5,015,345A or by Bergner and Hartmann in "Detection of damaged membranes in alkali chloride electrolysers", Journal of Applied Electrochemistry 24 (1994), pp. 1201-1205.

Due to the aging of the membranes, however, the permeability of the membranes for OH ions generally increases ^, so that depending on the properties of the membrane of a cell element, the lye entry into the anode chamber, which varies depending on the properties of a cell element, has such an effect that there are differences in the voltage curve. In 4 A typical start-up process is shown, which shows the different voltage curves of the individual elements depending on the electrolysis current I and operating time t due to different caustic permeability. So that the current yield can be quantified directly via the voltage curve at low electrolysis currents, methods can be derived from which the current yield can be calculated for each individual element via the curve of the cell voltage when starting up. Few methods are known for this purpose.

Rantala and Virtanen have in U.S. 7,122,109 B2 a voltage-based method is described how the current yield can be approximately determined by considering the difference between measured and theoretically expected voltage using a proportionality factor.

• Auslöser ist der geringe Polarisationsstrom von etwa 20 bis 50A, der bei der Chlor-Alkali-Elektrolyse den Zellelementen zugeführt wird, um nach Abschalten der Anlage zu verhindern, dass ohne elektrisches Feld Chlorat- und Hypochloritionen zur Kathodenseite diffundieren und dort die Edelmetallbeschichtung der Kathode auflösen, die für möglichst geringe Überspannungen bei der kathodischen Wasserstoffbildung sorgt. Mit Wirksamkeit des Polarisationsstroms wird nach Abschalten der Anlage der zeitabhängige Verlauf der einzelnen Elementspannungen beobachtet, bis für jedes Zellelement ein vordefiniertes Ereignis in Form einer bestimmten Elementspannung erreicht ist. Die Stromausbeuteberechnung der Einzelelemente erfolgt dann über eine Funktion, in der für jedes Element dessen spezifische Zeitdauer eingesetzt wird, die das Element braucht, um nach Einschalten des Polarisationsstroms diesen vorbestimmten Spannungswert zu erreichen.

Tremblay et al. describe in WO 2010/118533 A1 Another possible method, in which the current yield of each cell element at low electrolysis currents is calculated from the time-dependent voltage curve both when the electrolysis system is switched off and when it is started up using empirically determined cell parameters. In detail, the procedure provides for the following procedure:

• The trigger is the low polarization current of around 20 to 50A, which is fed to the cell elements in chlor-alkali electrolysis in order to prevent chlorate and hypochlorite ions from diffusing to the cathode side without an electric field and dissolving the precious metal coating of the cathode there after the system has been switched off , which ensures the lowest possible overvoltages during cathodic hydrogen formation. Once the polarization current has become effective, the time-dependent course of the individual element voltages is observed after the system has been switched off, until a predefined event in the form of a specific element voltage is reached for each cell element. The current yield of the individual elements is then calculated using a function in which the specific time required for each element to reach this predetermined voltage value after switching on the polarization current is used for each element.

When the system is switched on, the triggering time is also defined by switching on the polarization current and thus by the start-up, i.e. the start-up of the system. The electrolysis current is now raised to a specific value and the time-dependent course of the individual element voltages is observed. As in the case of switching off the electrolysis current, the specific time for each individual element is determined, which the individual element voltage needs to reach a predefined voltage value. The current yield of the individual elements is then calculated using a function in which this element-specific time period is used until the predetermined voltage value is reached after the polarization current has been switched on.

This time function is used by Tremblay et al. defined in such a way that it is based on an empirical model that takes into account a large number of electrolyser properties in numerical simulations, such as the magnitude of the polarization current, the volume of the anode compartment, the membrane area, the brine flow rate, the caustic concentration, the pH value, etc. An example of a Functions with five different parameters and logarithmic and exponential parts are also presented.

This approach has a number of disadvantages. If the electrolysis is switched off, there is a lot of free chlorine in the cell. This free chlorine intercepts the incoming OH ^- ions and reacts to form hypochlorite and chlorate. The anolyte pH thus remains below 7 in the acidic range and prevents the formation of oxygen that occurs in the alkaline range. The chemical basis for the process to function after the plant has been shut down is therefore only given to a limited extent.

The method also depends on a polarizing current being introduced. Depending on the stability of the noble metals of the cathode coating against free chlorine, however, no polarization current is required taken and such is therefore required neither when starting nor when switching off, so that the method described can not be carried out.

When starting up, a polarization current is not required when the electrolysis current is applied and is therefore sometimes only applied after the system and thus the electrolysis current have been switched on. Alternatively, the polarization current can also be applied 1-2 hours before switching on the electrolysis current as part of the switch-on preparations. It is therefore not clear how the exact start time for the evaluation of the voltage curves is to be defined and what influence the definition of the start time has on the calculation function for the individual element current yield.

An empirical function with many different regression parameters, all of which must be determined using appropriate modeling and taking into account the electrolyzer properties such as the cell design or the physical conditions, always leads to inaccuracies, since any change in a property that affects one or more regression parameters changes the basis of calculation for the empirical function changed. Changes in the electrolysis system in the form of individual newly designed cell elements in the electrolyzer, or changed operating conditions, aging effects, etc., will therefore be difficult to take into account and require mathematical adjustments.

The selection of the individual time period to be determined for each cell element as the basis variable for the calculation of the individual element current yield also leads to inaccuracies. Since the rate of current increase is not predetermined, the individual time until the voltage of each timing element reaches the predetermined level will differ depending on whether the current is increased rapidly or slowly. It is questionable whether the resulting changes are taken into account when determining the regression parameters.

It is therefore the object of the invention to provide an alternative method for determining the current yield for individual elements of an electrolyzer consisting of at least one individual element, which no longer has the stated disadvantages of the prior art. This means that the method according to the invention should be independent of the application of a polarization current, it should have a clearly defined starting point for the evaluation and element-specific, individual time durations for reaching a predetermined event should be allowed to remain unconsidered. In addition, the method should do without complex modeling to determine regression parameters and the method should do without taking cell design and operating conditions into account.

This object is achieved with the features of claim 1. Advantageous configurations of the invention result from the dependent claims.

1. a. ein Elektrolysestrom I auf einen Elektrolyseur bestehend aus mindestens einem Einzelelement i aufgebracht wird und der Elektrolysestrom I auf einen bestimmten Stromwert I_END angehoben wird, wobei I_END zwischen 1kA und 2,7kA liegt und insbesondere zwischen 1,8kA und 2,2kA liegt,
2. b. ein Zeitpunkt t₀ ermittelt wird, der willkürlich vor oder nach Einschalten des Elektrolysestroms gesetzt wird (das heißt, dass ein Zeitpunkt t₀ festgelegt wird, der frei wählbar vor oder nach Einschalten des Elektrolysestroms liegen kann), wobei der Elektrolysestrom einen bestimmten Maximalwert l₀ nicht überschreiten darf, wobei l₀ zwischen 10A und 200A liegt,
3. c. die Spannung U_i des mindestens einen Einzelelements i gemessen wird und der Mittelwert aller Einzelelementspannungen UM gebildet wird,
4. d. der Zeitpunkt t_END bestimmt wird, nach dem alle Zellspannungen U_i der Einzelelemente i einen definierten Spannungsunterschied ΔU_END vom Mittelwert aller Einzelelementspannungen UM abweichen, wobei ΔU_END zwischen 10mV und 200mV liegt,
5. e. die Fläche A_i unter der Spannungskurve U_i(x) jedes Einzelelements i über numerische Integration über die Variable x in den Grenzen zwischen x₀ = x(t₀) und x_END = x(t_END) bestimmt wird:

$$A_i={\displaystyle \underset{x_0}{\overset{x_{END}}{\int }}{U}_i\left(x\right)dx}$$

1. f. die Fläche AM unter der Spannungskurve des Durchschnitts aller Einzelelemente UM (x) über numerische Integration über die Variable x in den Grenzen x(t₀) und x(t_END) bestimmt wird: $$A_M={\displaystyle \underset{x_0}{\overset{x_{END}}{\int }}{U}_M\left(x\right)dx}$$
   
2. g. die durchschnittliche Elektrolyseurstromausbeute CE_EL bestimmt wird,
3. h. die Stromausbeute CE_i jedes Einzelelements i abhängig von der Elektrolyseurstromausbeute CE_EL über eine empirische Funktion f berechnet wird, die das Flächenverhältnis A_i / A_M beinhaltet.

The invention provides that the current yield of the individual elements of an electrolyzer, comprising at least one individual element, is determined by means of a surface comparison, which can be carried out for each element each time an electrolysis system is started up. This is done in such a way that:

1. a. an electrolysis current I is applied to an electrolyzer consisting of at least one individual element i and the electrolysis current I is increased to a specific current value I _END , with I _END being between 1kA and 2.7kA and in particular between 1.8kA and 2.2kA,
2. b. a point in time t ₀ is determined, which is set arbitrarily before or after the electrolysis current is switched on (that is, a point in time t ₀ is specified, which can be freely selectable before or after the electrolysis current is switched on), the electrolysis current having a specific maximum value l ₀ must not exceed l ₀ between 10A and 200A,
3. c. the voltage U _i of the at least one individual element i is measured and the mean value of all individual element voltages UM is formed,
4. i.e. the time t _END is determined after which all cell voltages U _i of the individual elements i deviate by a defined voltage difference ΔU _END from the mean value of all individual element voltages UM, with ΔU _END being between 10 mV and 200 mV,
5. e. the area A _i under the voltage curve U _i (x) of each individual element i is determined by numerical integration over the variable x in the limits between x ₀ = x(t ₀ ) and x _END = x(t _END ):

$$A_i={\displaystyle \underset{x_0}{\overset{x_{END}}{\int }}{u}_i\left(x\right)\mathrm{i.e}x}$$

1. f. the area AM under the stress curve of the average of all individual elements UM (x) is determined by numerical integration over the variable x in the limits x(t ₀ ) and x(t _END ): $$A_M={\displaystyle \underset{x_0}{\overset{x_{END}}{\int }}{u}_M\left(x\right)\mathrm{i.e}x}$$
   
2. G. the average electrolyser current yield CE _EL is determined,
3. H. the current yield CE _i of each individual element i is calculated as a function of the electrolyzer current yield CE _EL using an empirical function f that contains the area ratio A _i /A _M .

The core idea of the invention is therefore to empirically derive the current yield of the individual elements by purely comparing them. According to the state of the art, the current yield of the electrolyser, ie the average of all individual elements CE _EL , can be calculated using anodic or cathodic balances. The course of the average voltage UM of all individual elements when starting up to a specific current level at which the formation of oxygen no longer takes place due to the resulting voltage and thus potential level or becomes negligible due to the formation of chlorine, is therefore to be interpreted as a measure of the average current yield CE _EL . If the area under the voltage curve is determined when plotted against a suitable influencing parameter between a start and end time to be defined, this value A _M is a measure of the amount of lye determining the anodic potential and thus the voltage, and thus also the current yield CE _EL .

If the area under the stress curve of each individual element is plotted against the appropriate influencing parameter to be selected, i.e. the variable x, and determined between the same start and end times as for the stress average, a quotient of the element-specific area A _i in relation to the Area A _M a value that tends to show for each individual element how strong the caustic diffusion and thus the current yield is compared to the average. Multiplying the quotient by the average current yield CE _EL thus leads to a measured value for the individual element current yield CE _i .

According to the invention, either the time t or the electrolysis current I is used as the variable x.

In an embodiment of the invention, a cathodic balance is carried out to determine the electrolyzer current yield CE _EL by circulating a quantity of lye supplied to the electrolyzer and the quantity of lye produced in the electrolyzer in a closed circuit between the electrolyzer and a lye collecting tank, with the current load being kept constant for a specific period of time the fill level of the lye collection tank is kept constant by the amount of lye produced being discharged from the circuit, the concentration and volume flow of the amount of lye produced being measured in the process, and the current yield for the given period of time according to equation (2) via the ratio of the amount of lye produced is calculated for the theoretically possible lye production quantity dependent on the electricity load.

In an alternative embodiment, an anodic balance is carried out to determine the electrolyzer current yield CE _EL , with the sodium sulfate _{concentration} present in the brine C _Na2SO4 and in the anolyte C'Na2SO4 being measured before and after the electrolysis, the ratio of the amount of sulfate in the brine and anolyte being formed and the anolyte volume flow V̇' is determined according to equation (3) by multiplication with the measured brine volume flow V̇, then the concentrations of oxygen y _O2 and chlorine gas y _Cl2 in the product gas, the concentrations of sodium hydroxide C _NaOH , sodium chlorate C _NaClO3 , sodium carbonate C _Na2CO3 and hydrochloric acid C _HCl in the brine, and the concentrations of sodium sulfate C' _Na2SO4 , hypochlorite C' _HOCl and hydrochloric acid C' _HCl in the anolyte are determined and the current yields of the anolyte components Δ _i are determined according to equations (4) to (9) and finally the Current efficiency CE is calculated summarily via equation (10).

durchgeführt, wobei I der Elektrolysestrom, Q_A der dem Zellelement zugeführte Säurevolumenstrom, d_A die Dichte der Säure, c_A die Massenkonzentration der verwendeten Säure, y_O2 der Sauerstoffgehalt im anodischen Produktgas, P1 ein empirisch bestimmter Parameter ist, der vorzugsweise zwischen 98,5% und 99,5% und insbesondere zwischen 98,9% und 99,1% liegt, P2 ein empirisch bestimmter Parameter, der vorzugsweise zwischen 0,05 und 0,10 % und insbesondere zwischen 0,07 und 0,09 % liegt und P3 ein empirisch bestimmter Parameter ist, der vorzugsweise zwischen 2,0% und 3,0% und insbesondere zwischen 2,4% und 2,6% liegt.In another alternative embodiment, a simplified anodic balance according to the formula is used to determine the electrolyzer current yield CE _EL $${\text{CE}}_{\text{el}}=\text{<figure-callout id="1" label="P" filenames="DE102011110507B4\_0039.png,DE102011110507B4\_0040.png" state="{{state}}">P</figure-callout>}1-\left(\text{P2/I}\right)\times \left({\text{Q}}_{\text{A}}\times {\text{i.e}}_{\text{A}}\times {\text{c}}_{\text{A}}\right)+\left(0.5-{\text{y}}_{\text{O2}}\right)\times \text{<figure-callout id="3" label="P" filenames="DE102011110507B4\_0040.png" state="{{state}}">P</figure-callout>}3$$

carried out, where I is the electrolysis current, Q _A is the acid volume flow supplied to the cell element, d _A is the density of the acid, c _A is the mass concentration of the acid used, y _O2 is the oxygen content in the anodi product gas, P1 is an empirically determined parameter, which is preferably between 98.5% and 99.5% and in particular between 98.9% and 99.1%, P2 is an empirically determined parameter, which is preferably between 0.05 and 0 .10% and in particular between 0.07 and 0.09% and P3 is an empirically determined parameter which is preferably between 2.0% and 3.0% and in particular between 2.4% and 2.6%.

In a further alternative embodiment of the determination of the electrolyzer current yield CE _EL direct online measurement methods are used. These online measurement methods are known to those skilled in the art from the prior art.

aufweist, wobei K1 ein empirischer Parameter ist, der vorzugsweise zwischen 0,8 und 1,2 liegt und insbesondere zwischen 0,95 und 1,05, und K2 ein empirischer Exponent ist, der vorzugsweise zwischen 0,1 und 1,0 liegt und insbesondere zwischen 0,3 und 0,7.Investigations have shown that the quotient A _i / A _M is not directly proportional to the current yield of the individual elements. By choosing suitable sampling points on the individual element, the current yield can be precisely determined analytically via the anodic balance. These results can be used as a basis for determining empirical adjustment parameters. These parameters as multiplier K1 or exponent K2 iteratively adjusted accordingly lead to a very good agreement between the analytically determined current yield and the individual element current yield determined via the voltage curve when starting up, so that in one embodiment of the method according to the invention the empirical function has the form $$C{E}_i=C{E}_{EL}\times \mathrm{<figure-callout\; id="1"\; label="K"\; filenames="DE102011110507B4\_0039.png,DE102011110507B4\_0040.png"\; state="\{\{state\}\}">K</figure-callout>}1\times {\left\{\frac{A_i}{A_M}\right\}}^{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102011110507B4\_0036.png,DE102011110507B4\_0040.png"\; state="\{\{state\}\}">K</figure-callout>}2}$$

wherein K1 is an empirical parameter, preferably between 0.8 and 1.2, and in particular between 0.95 and 1.05, and K2 is an empirical exponent, preferably between 0.1 and 1.0, and in particular between 0.3 and 0.7.

erfolgt, wobei F eine produktspezifische Faradaykonstante mit der Einheit [t/kAh] bezeichnet, die über den Quotienten aus molarer Faradaykonstante und Molmasse des Produkts gebildet wird.Once the individual element current yield CE _i is known, Equation 1 can also be used to carry out an economic evaluation of each individual element by calculating the specific energy consumption in kWh/t product for each individual element of an electrolyzer from the individual element voltage U _i and the current yield CE _i via the relationship $${\text{EV}}_{\text{i}}={\text{u}}_{\text{i}}\text{/}\left(\text{f}\times {\text{CE}}_{\text{i}}\right)$$

takes place, where F designates a product-specific Faraday constant with the unit [t/kAh], which is formed via the quotient of the molar Faraday constant and the molar mass of the product.

A further advantage of the method according to the invention is the independence from the polarization current and from the individual time factor until a certain voltage level is reached, as suggested by Tremblay et. al. described as necessary. Whether the start time of the calculation is selected exactly when switching on or shortly before or after does not contribute to the area comparison. It is also irrelevant whether the end point is reached when a specific stress level is reached or some time later, since this time factor has no influence on the area comparison. In this respect, the presence of a polarization current does not have to be taken into account.

In the simplest case, the areas can be determined by evaluating the voltage as a function of the operating time t. Alternatively, the area calculation can also be determined as a function of the electrolysis current I. The advantage of this procedure is complete independence from the speed at which the electrolysis current is increased per unit of time until the target level of e.g. 2.5 kA is reached.

$$\Delta {\text{A}}_{\text{M}}\left(\text{t}\right)=\mathrm{0,5}\times \left({\text{U}}_{\text{M}}\left(\text{t}\right)+{\text{U}}_{\text{M}}\left(\text{t}+\Delta \text{t}\right)\right)\times \Delta \text{t}$$

The determination of the areas in applications against the variable operating time t is in 5 shown. Since the areas cannot be determined using classic mathematical integration, a numerical method must be used. Accordingly, a fixed Δt is added from the starting time t ₀ and the voltages are determined at each time t and t+Δt both for each individual element and for the voltage average. The corresponding area can then be determined using the area equation for a trapezoid, i.e $$\Delta {\text{A}}_{\text{i}}\left(\text{t}\right)=0.5\times \left({\text{u}}_{\text{i}}\left(\text{t}\right)+{\text{u}}_{\text{i}}\left(\text{t}+\Delta \text{t}\right)\right)\times \Delta \text{t}$$

$$\Delta {\text{A}}_{\text{M}}\left(\text{t}\right)=0.5\times \left({\text{u}}_{\text{M}}\left(\text{t}\right)+{\text{u}}_{\text{M}}\left(\text{t}+\Delta \text{t}\right)\right)\times \Delta \text{t}$$

Adding up all ΔA _i (t) between t ₀ and t _END then leads to the total area Ai, the same applies to all ΔA _M (t) to A _M .

$$\Delta {\text{A}}_{\text{M}}\left(\text{l}\right)=\mathrm{0,5}\times \left({\text{U}}_{\text{M}}\left(\text{l}\right)+{\text{U}}_{\text{M}}\left(\text{l}+\Delta \text{l}\right)\right)\times \Delta \text{l}$$

For the electrolysis current as variable I, the calculation proceeds in the same way. Accordingly, from the starting time t ₀ the electrolysis current I(t ₀ ) is chosen as the starting value and a ΔI is added and the voltages for each I and I+ΔI are determined both for each individual element and for the voltage average. The corresponding area can then be determined using the area equation for a trapezoid, i.e $$\Delta {\text{A}}_{\text{i}}\left(\text{l}\right)=0.5\times \left({\text{u}}_{\text{i}}\left(\text{l}\right)+{\text{u}}_{\text{i}}\left(\text{l}+\Delta \text{l}\right)\right)\times \Delta \text{l}$$

$$\Delta {\text{A}}_{\text{M}}\left(\text{l}\right)=0.5\times \left({\text{u}}_{\text{M}}\left(\text{l}\right)+{\text{u}}_{\text{M}}\left(\text{l}+\Delta \text{l}\right)\right)\times \Delta \text{l}$$

Adding up all ΔAi(I) between I ₀ and I _END then leads to the total area Ai, the same applies to all ΔA _M (I) to A _M .

Furthermore, the invention provides that the cell elements are categorized into groups depending on the amount by which the current yield of the individual element deviates from the average current yield of all elements.

In one embodiment of the invention, 4 categories are provided here, which are defined by absolute percentage deviations from the average percentage current yield of all elements, with category 1 being assigned the individual elements that are at least 0.5%, preferably 1%, above the current yield average, a category 2 the individual elements are assigned which are up to 2% preferably up to 1% above or below the average current yield, a category 3 is assigned the individual elements which are at least 1% preferably at least 2% below the average current yield of all elements and category 4 the individual elements are assigned that have at least 3% below the current efficiency average of all elements or absolutely below 90% current efficiency. Category 1 individual elements are therefore individual elements that work particularly well, category 2 individual elements that work to a normal extent, category 3 individual elements represent individual elements that function below average and category 4 individual elements are ultimately defective elements.

In a further option of the invention, the elements can be assigned to categories via visual color representations. As an example, the results of the assignments to category 1 are shown in blue, assignments to category 2 in green, assignments to category 3 in yellow and assignments to category 4 in red.

The present invention also includes a system for determining the current efficiency of the individual elements of an electrolyzer, comprising: a processor in a computer system, a data memory in communication with the processor, and an execution element in communication with and configured for the processor to carry out a method according to claim 1.

This system particularly preferably includes a screen for receiving and displaying the data used to determine the current yield of the individual elements of the electrolyzer and for displaying the result of the current yield determined for the individual elements.

Such a system is in 7 shown as an example. The system 1 comprises an execution element 2 which is controlled via a processor 3, the processor 3 being coupled to the data memory 4. An electrolyzer 5 is connected to the system 1 and comprises a plurality of single element cells.

The data memory 4 is used to receive and store data required by the system 1 in order to determine the current yield of the individual elements of an electrolyzer according to the method according to the invention, which can be called up by the processor 3 . The processor 3 and the data memory 4 are commercially available computer accessories known to those skilled in the art that are suitable for performing such operations. The execution element 2 is in turn composed of several modules, which receive the measured data of the individual elements of the electrolyzer 5 and calculate them according to the method according to claim 1 in order to deliver the current yield of the individual elements to be determined as a result. The formulas presented above serve as a basis for this. The results are finally displayed on a screen 6 for each individual element.

Furthermore, the disclosure of the present invention includes a computer program on a computer-readable medium containing instructions for determining the current efficiency of the individual elements according to the method of claim 1.

• - Unabhängigkeit vom Anlegen eines Polarisationsstroms
• - Freiheitsgrade beim Start- und Endpunkt für die Auswertung
• - Keine Berücksichtigung von elementspezifischen, individuellen Zeitdauern zum Erreichen eines vorgegebenem Ereignisses
• - Keine Berücksichtigung von aufwändigen Modellierungen zur Ermittlung von Regressionsparametern
• - Keine Berücksichtigung von Zelldesign und Betriebsbedingungen

Advantages resulting from the invention:

• - Independence from applying a polarization current
• - Degrees of freedom at the start and end point for the evaluation
• - No consideration of element-specific, individual time durations to reach a given event
• - No consideration of complex modeling to determine regression parameters
• - No consideration of cell design and operating conditions

character list

• 1 graphical representation of the electrode potentials as a function of the electrolysis current and the corresponding electrochemical partial reactions
• 2 Graphic representation of the electrode potentials when using an anode coating to illustrate the effect on the change in the potential curves for oxygen formation and chlorine formation
• 3 graphical representation of the pH dependence of the potential profile of anodic oxygen formation
• 4 Typical voltage curves of the individual elements and the electrolysis current when starting an electrolyser
• 5 Diagram for the basic representation of the surface determination of stresses depending on the operating time t
• 6 Diagram for the basic representation of the area determination of voltages depending on the electrolysis current I
• 7 Schematic representation of a system according to the invention for determining the current yield of the individual elements of an electrolyzer using the method according to the invention

symbol:

symbol meaning Unit ΔA _i Partial area under the stress curve of the individual element [-] ΔA _M Partial area under the average stress curve [-] Δt time interval [n] ΔI current change [n/a] ΔU voltage change [V] ΔU _i Voltage difference element i to mean [V] _Δi Individual current yield of a component i [%] A _i Area under the stress curve of the single element [-] _AM Area under the voltage curve of the electrolyser [-] c _A Mass concentration of the acid [kg/kg] C _i Concentration of a component i in the brine [g/l] c _i ' Concentration of a component i in the anolyte [g/l] CE current yield [%] CE _EL Average current yield of all individual elements [%] CE _i Current efficiency of the single element [%] d _a density of hydrochloric acid [kg/l] EV specific energy consumption [kWh/t] EV _i specific energy consumption of the individual element [kWh/t] f specific Faraday constant [t/kAh] I electrolysis current [n/a] K1 empirical parameter [-] K2 empirical parameter [-] M _P practically formed amount of product [kg] _MT theoretically possible product quantity [kg] P1 parameter [%] p2 parameter [%kg/kAh] P3 parameter [%] Q _A acid flow rate [l/h] t time [n] u tension [V] u _i single element voltage [V] U _M Average voltage of all individual elements [V] V̇ brine volume flow [ ^m3 /h] V̇' anolyte flow rate [ ^m3 /h] x variable [-] y _Cl2 Chlorine content in the product gas [-] y _O2 Oxygen content in the product gas [-]

Reference List

1

system

2

execution element

3

processor

4

data storage

5

electrolyser

6

Screen

Claims (12)

Method for determining the current yield of the individual elements of an electrolyzer comprising at least one cell element of an electrolyzer, characterized in that a. an electrolysis current I is applied to an electrolyzer consisting of at least one individual element and the electrolysis current I is increased to a specific current value I _END in the range of 1 kA and 2.7 kA, b. a point in time t ₀ is set, which can be freely selectable before or after the electrolysis current is switched on, the electrolysis current not being allowed to exceed a certain maximum value I ₀ between 10 A and 200 A, c. the voltage U _i of the at least one individual element is measured and the mean value of all individual element voltages UM is formed, d. the point in time t _END is determined after which all cell voltages U _i of the individual elements i deviate by a defined voltage difference ΔU _END from the mean value of all individual element voltages UM, ΔU _END being between 10 mV and 200 mV, e. the area A _i under the voltage curve U _i (x) of each individual element i is determined by numerical integration over the variable x in the limits between x ₀ = x(t ₀ ) and x _END = x(t _END ): $$A_i={\displaystyle \underset{x_0}{\overset{x_{END}}{\int }}{u}_i\left(x\right)\mathrm{i.e}x}$$

where the variable x stands for either the time t or the electrolysis current I; f. the area AM under the stress curve of the average of all individual elements UM (x) is determined by numerical integration over the variable x in the limits x(t ₀ ) and x(t _END ): $$A_M={\displaystyle \underset{x_0}{\overset{x_{END}}{\int }}{u}_M\left(x\right)\mathrm{i.e}x}$$

where the variable x also stands for either the time t or the electrolysis current I; G. the average electrolyzer current yield CE _EL is determined, and h. the current yield CE _i of each individual element i is calculated as a function of the electrolyzer current yield CE _EL using an empirical function f that contains the area ratio A _i /A _M . procedure after claim 1 characterized in that a cathodic balance is carried out to determine the electrolyzer current yield CE _EL , with an amount of lye fed to the electrolyzer and an amount of lye produced in the electrolyzer being circulated in a closed circuit between the electrolyzer and an lye collection tank, with the current load being kept constant for a specific period of time the fill level of the caustic collection tank is kept constant by discharging the produced quantity of caustic from the circuit, the concentration and the volume flow of the produced quantity of caustic are measured during discharge, and the current yield CE _EL for the given period of time according to the equation $${\text{CE}}_{\text{el}}=100\times {\text{M}}_{\text{P}}{\text{/M}}_{\text{T}}\left[\text{\%}\right]$$

is calculated via the ratio of the amount of lye produced M _P to the theoretically possible amount of lye produced, M _T , which depends on the electricity load. procedure after claim 1 and/or 2, characterized in that an anodic balance is carried out to determine the electrolyzer current yield CE _EL , the sodium sulfate _{concentration} present in the brine C _Na2SO4 and in the anolyte C'Na2SO4 being measured before and after the electrolysis, the ratio of the amount of sulfate in the brine and anolyte is formed and the anolyte volume flow V̇' according to the equation $${\dot{V}}^{\text{'}}=\dot{V}\frac{C_{Na2SO4}}{C_{Na2SO4}^{\text{'}}}$$

is determined by multiplication with the measured brine volume flow V̇, then the concentrations of oxygen v _O2 and chlorine gas v _Cl2 in the product gas, the concentrations of sodium hydroxide C _NaOH , sodium chlorate C _NaClO3 , sodium carbonate C _Na2CO3 and hydrochloric acid C _HCl in the brine, and the concentrations of Sodium chlorate C' _Na2SO4 , hypochlorite C' _HOCl and hydrochloric acid C' _HCl are determined in the anolyte and the current yields of the anolyte components Δ _i are determined according to the following equations: $$n_{NaClO3}=\frac{C_{NaClO3}^{\text{'}}\cdot {\dot{V}}^{\text{'}}-C_{NaClO3}\cdot \dot{V}}{n\cdot I\cdot 0.662}\cdot 100\text{\%}$$

$$n_{HOCl}=\frac{C_{HOCl}^{\text{'}}\cdot {\dot{V}}^{\text{'}}}{n\cdot I\cdot 0.980}\cdot 100\text{\%}$$

$$n_{HCl}=\frac{C_{HCl}\cdot \dot{V}-C_{HCl}^{\text{'}}\cdot {\dot{V}}^{\text{'}}}{n\cdot I\cdot 1.36}\cdot 100\text{\%}$$

$$n_{Alkali}=\frac{C_{NaOH}\cdot \dot{V}}{n\cdot I\cdot 1.4923}\cdot 100\text{\%}$$

$$n_{Na2CO3}=\frac{C_{Na2CO3}\cdot \dot{V}}{n\cdot I\cdot 1.978}\cdot 100\text{\%}$$

and finally the current yield CE _EL is calculated using the following equation: $$C{E}_{EL}=100\%-n_{O2}-n_{NaClO3}-n_{HOCl}-n_{HCl}+n_{Na2CO3}+n_{Alkali}$$

Procedure according to one of Claims 1 until 3 , characterized in that to determine the electrolyzer current yield CE _EL a simplified anodic balance according to the formula $${\text{CE}}_{\text{el}}=\text{P}1-\left(\text{P2/I}\right)\times \left({\text{Q}}_{\text{A}}\times {\text{i.e}}_{\text{A}}\times {\text{c}}_{\text{A}}\right)+\left(0.5-{\text{y}}_{\text{O2}}\right)\times \text{P}3$$

is carried out, where I is the electrolysis current, Q _A is the acid volume flow fed to the cell element, d _A is the density of the acid, c _A is the mass concentration of the acid used, y _O2 is the oxygen content in the anodic product gas, P1 is an empirically determined parameter, which is preferably between 98 .5% and 99.5%, P2 is an empirically determined parameter which is preferably between 0.05 and 0.10% and P3 is an empirically determined parameter which is preferably between 2.0% and 3.0%. Procedure according to one of Claims 1 until 4 , characterized in that direct online measurement methods are used to determine the electrolyzer current yield CE _EL . Procedure according to one of Claims 1 until 5 , characterized in that the empirical function has the form $$C{E}_i=C{E}_{EL}\times K1\times {\left\{\frac{A_i}{A_M}\right\}}^{K2}$$

where K1 is an empirical parameter, preferably between 0.8 and 1.2, and K2 is an empirical exponent, preferably between 0.1 and 1.0. Procedure according to one of Claims 1 until 6 , characterized in that a calculation of the specific energy consumption in kWh/t product for each individual element of an electrolyzer from the individual element voltage U _i and the current yield CE _i via the relationship $${\text{EV}}_{\text{i}}={\text{u}}_{\text{i}}\text{/}\left(\text{f}\times {\text{CE}}_{\text{i}}\right)$$

takes place, where F designates a product-specific Faraday constant with the unit [t/kAh], which is formed via the quotient of the molar Faraday constant and the molar mass of the product. Procedure according to one of Claims 1 until 7 , characterized in that the cell elements are categorized into groups depending on the amount by which the current yield of the individual element CE _i deviates from the average current yield of all elements CE _EL . procedure after claim 8 , characterized in that the cell elements are divided into 4 categories, which are defined by absolute percentage deviations from the average percentage current yield of all elements, category 1 being assigned to those individual elements which are at least 0.5%, preferably 1%, above the average current yield, Category 2 is assigned to those individual elements that are up to 2%, preferably up to 1% above or below the average current yield, Category 3 is assigned to those individual elements that are at least 1%, preferably at least 2%, below the average current yield of all elements, and Category 4 those individual elements are assigned that have at least 3% below the current yield average of all elements or absolutely below 90% current yield. procedure after claim 9 , characterized in that the elements are assigned to categories via visual color representations. System for determining the current efficiency of the individual elements of an electrolyser, comprising: (i) a processor in a computer system, (ii) a data memory connected to the processor, (iii) an execution element connected to and for the processor is configured, a procedure according to claim 1 to perform. system after claim 11 , comprising a screen for receiving and displaying the data used to determine the current yield of the individual elements of the electrolyzer.

Images