WO2013023733A2 - Method for determining the individual current efficiency in an electrolyser - Google Patents

Abstract

The invention relates to a method for determining the current efficiency of the individual elements in an electrolyser comprising at least one cell element of an electrolyser. For this purpose, a method is described, wherein an electrolysis current I is applied to an electrolyser comprising at least one individual element and is raised to a specific current value; a time is determined, which is set randomly before or after the electrolysis current is switched on, wherein the electrolysis current must not exceed a specific maximum value; the voltage U­_i of the at least one individual element i is measured and the average of all the individual element voltages U_M is measured; a time t_END is determined, after which all the cell voltages of individual elements deviate by a defined voltage difference from the average of all the individual element voltages; the area A_i under the voltage curve of each individual element is determined via numerical integration over a suitable variable x in the limits between x₀ = x_(t0) und x_END = x(t_END); the area A_M under the voltage curve of the average of all the individual elements is determined by numerical integration against the variable x in the limits x(t₀) and x(t_END); the average electrolyser current efficiency is determined via a method according to the prior art; the current efficiency of each individual element is calculated as a function of the electrolyser current efficiency via an empirical function, wherein the empirical function includes the area ratio A_i / A_M.

Description

 Method for determining the single-element current efficiency in the electrolyzer

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

The voltage U and the current efficiency CE of a cell element of an electrolyzer are important parameters in the context of electrolysis technology, since of these

physical quantities of electricity or energy consumption EV of the electrolyzer depends on the exact knowledge of the economic operation of a technical electrolysis plant is of importance.

The energy consumption of an electrolyzer is for the sake of practical

Assessment usually based on the mass of product and thus specifically shown. According to Bergner, "Development status of alkali chloride electrolysis, Part 2", Chemie-Ingenieur-Technik 66 (1994) No. 8, the direct proportional relationship between specific energy consumption and voltage can be calculated for classical chlor-alkali electrolysis as follows:

(1) EV = U / (F x CE) [kWh / t]

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

The second important proportionality factor is the current efficiency CE, which indicates the percentage ratio of practically formed product amount M _P and theoretically possible product amount M _T due to the charges used: (2) CE = 100 × M _P / M _T [%]

Due to charge losses due to stray currents, thermodynamic

Side reactions or even membrane damage, is lost by the product is the

Current efficiency always less than 100%. Since the energy consumption of an electrolyzer is the decisive criterion for the economic operation of a technical electrolysis plant, assuming a constant current efficiency of all individual cell elements of the relationship of amperage and cell or Elektrolyseurspannung is sufficient for the assessment of economic operation. However, if the current efficiency CE is not constant, the most precise possible assessment of a cell element for economic operation can only be achieved via the

Determination and monitoring of specific energy consumption EV in direct

Dependence of the current yield to be determined in parallel. The current efficiency CE of each cell element can not be measured differently than the voltage U. Rather, the actual product quantity of each cell element must be determined from practical analyzes in order to arrive at usable results for the adequate determination of the energy consumption. Cowell, Martin and Revill have the well-known empirical methods on the cathode-side or anode-side

Balances of the product are detailed 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).

According to Cowell, Martin and Revill the best known method is the so-called

"Cathodic balance" or "caustic soda collection method". This requires the circulation of the leachate over a longer period of time in a closed circuit, in which the power load is measured exactly. The circulated amount in the circulation is kept constant and the produced amount of leach is continuously discharged, whereby concentration and flow rate of the produced liquor must be measured exactly. The current efficiency is then determined by the ratio of the produced quantity of leachate in comparison to the theoretically possible produced quantity of leachate during the mentioned longer period. Disadvantage of this method is the restriction to the entire plant, the production volume of a single electrolyzer or individual cells can not be determined so.

Among other indirect methods Cowell, Martin and Revill introduce the "sulfate key" method, which has become established as the so-called "anodic balance". In this

Method is determined by the sodium sulfate concentration in brine and anolyte, ie before and after the reaction, the Anolyte flow rate, since sulfate is not changed by the electrochemical reactions in the cell. By ratio formation of the sulfate amounts in brine and anolyte and multiplied by the brine flow, the anolyte volumetric flow can be determined, which is referred to as the "sulfate key." The amount of product is then determined by comparing the components in the brine with the components formed in anolyte and chlorine gas.

In detail, the following sizes are required for the anodic balance:

The electrolysis current I [kA]

The brine volume flow V [m ³ / h]

An analysis of the following gas components in the anodic product gas:

Chlorine y _C i2 [% v / v]

Oxygen y ₀ 2 [% v / v]

An analysis of the following mass-related concentrations in the brine (educt):

 Sodium hydroxide C SOH [g / i]

 Sodium sulfate C a2SO4 [g / i]

 Sodium Carbonate CNa2C03 [g / i]

 Sodium chlorate CNaClO3 [g / i]

 Hydrochloric acid CHCI [g / i]

An analysis of the following mass-related concentrations in the anolyte (product):

 Sodium sulfate C'Na2SO4 [g / i]

 Sodium chlorate C'NaClO3 [g / i]

 Hypochlorite C'HOCI [g / i]

Hydrochloric acid C'HCI [g / i]

After analysis of the required concentration, the calculation of the Anolytvolumenstroms F 'on the ratio of the sulfate concentration in feed brine and drain anolyte, ie the application of the "sulfate key" is carried out first:

 C

(3) V '= V ^N " ^lSOt

^ Na ₂ SO,

(5) rinoa = ^C'"^{oa 'V}' ^■ 100% In the next step, the yields of the different anolyte components are calculated:

(5) rinoa = ^C '' ^{oa 'V} ' ^■ 100%

, ^HOCl nl 0.980

 C V - C - V '

(6) η _Ηα = " ^a " ° - 100%

 C · F

(8) 7 _{to C} o = - ^ 100%

' ^N " ^2C ° ³ - 1,978

(9) o ₂ - / 7 " _{flC / O3} - / 7" _oa )%

 The current efficiency CE can be summarily summarized in the

Determine individual current yields calculated in Equations (4) to (9):

(10) CE = 100% - η _0ι - η _Νααθ} - η _Ηοα - η _Ηα + η _Ναι00 , + IAIM

The anodic balance offers over the cathodic balance the advantage that can be determined by sampling of brine and anolyte and chlorine gas from individual cells whose current efficiency by analytical means. A drawback is the complexity of the apparatus, which is required to determine the current yield of individual elements in the form of additional sampling points and time-consuming, personnel-binding analyzes.

Recently, a simplified anodic balance has been developed through an empirical approach to minimizing the overhead of analysis. Accordingly, an evaluation has shown that the current efficiency according to the anodic balance of essentially two

Size depends on the oxygen content in the product gas y ₀₂ and the hydrochloric acid volume flow in the feed brine Q _A. Taking into account density d _A and mass concentration of hydrochloric acid c _A , the following approximate formula is derived, where P1, P2 and P3 are constants to be determined empirically:

(1 1) CE = P1 - (P2 / 1) x (Q _A xd _A xc _A ) + (0.5 - y ₀₂ ) x P3

In addition to the cathodic balance and the variants of the anodic balance, there are various approaches to the indirect analysis methods for determining the current efficiency by direct - so-called online measuring methods such as the voltage measurement - to replace. These processes make use of the following electrochemical relationship: As shown in FIG. 1, anodic chlorine formation takes place in one

 Standard potential of 1.36V at 25 ° C against normal hydrogen electrode, while the cathodic hydrogen formation has a standard potential of -0.83V at 25 ° C. The thermodynamic decomposition voltage - ie the difference between the two potentials - is thus theoretically 2.19V. The anodic oxygen formation is thermodynamically even cheaper, since the standard potential is even a maximum of 1, 23V at 25 ° C even in the acidic pH range. In practice, therefore, an anodic noble metal coating is applied to the anode in order to increase the overvoltage for the formation of oxygen and thus promote chlorine formation. This situation is shown in Fig. 2, which the resulting

Potential courses of chlorine and oxygen formation at correspondingly coated anodes shows. However, the formation of oxygen depends strongly on the pH in the anolyte, as illustrated in FIG. 3. At low cell current efficiency, ie when larger amounts of OH ^" ions pass through membrane holes into the anode space, for example, the pH increases and the potential for oxygen formation is shifted to lower values, thus favoring the formation of oxygen again at low flow rates resulting

Potential difference and thus element voltage is lower than in the anodic

Chlorine formation. The more OH ^" ions penetrate into the anode space, the lower the anode potential and thus the resulting cell voltage

Electrolytic current increased so far that the chlorine formation potential is exceeded, so the formation of chlorine is in turn the thermodynamically more favorable reaction. The increasing turbulence due to the formation of chlorine gas bubbles also leads to the fact that the small amount of OH ions penetrating into the anode compartment is removed from the anode surface and under

Hypochlorite formation can be neutralized. As the electrolysis current increases, the proportion of oxygen formation is so low that only the chlorine potential contributes significantly to the anodic potential and the element voltage. Significant differences between the elements in the form of electrolysis voltage, by penetrating brine and subsequent

 Oxygen formation is influenced, and thus in the current efficiency can thus be observed only at low electrolysis currents up to about 2.2kA.

This effect can first be used qualitatively to detect elements with membrane damage when starting up an electrolysis plant, in which the Voltage behavior of the individual elements is monitored. If the voltage is significantly lower at an initial level increase of the electrolysis current to a certain level in the range of 1 -2 kA, the entry of significant amounts of OH ^" ions in the

Detecting anode compartment due to membrane damage. This process has long been known in the art and, for example, by Traini, Mojana and Gusmini in US Pat. No. 5,015,345 or by Bergner and Hartmann in "Detection of damaged membranes in alkali chlorides

electrolysers ", Journal of Applied Electrochemistry 24 (1994), p.1201-1205.

By aging of the membranes but generally takes the permeability of the

Membranes for OH ^" ions too, so that depending on the characteristics of the membrane of a

Cell element different liquor entering the anode compartment during startup effects such that there are differences in the voltage curve. FIG. 4 shows a typical start-up course which shows the different voltage profiles of the individual elements as a function of the electrolysis current I and the operating time t due to different liquor permeability. In order to detect damage in the individual cells, the measured voltages of the

 Single cells compared with each other, which is very expensive. In order to be able to quantify the current yield 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 course of the cell voltage. For this purpose, few methods are known.

Rantala and Virtanen have described a voltage-based method in US Pat. No. 7,122,109, how the current efficiency can be determined approximately by comparing the difference between measured and theoretically expected voltage by way of a proportionality factor. This method is disadvantageous. Rantala and Virtanen specifically describe that the theoretically expected stress is based only on temperature, electrolyte composition and current as well as design parameters such as the electrode spacing. However, the decisive factor for the course of the cell voltage during start-up is as described above by Bergner and Hartmann in "Detection of damaged membranes in alkali Chloride electrolysers", Journal of Applied

Electrochemistry 24 (1994) described the measure of leaching penetration through the membrane as the OH ^" concentration determines the anodic potential, the deciding factor being the membrane, which changes in size due to expansion and swelling effects, so that at each start-up the permeability to OH ^" ions, for example, by changing the hole position at defective membranes against the hole at least partially

Covering anodic electrode is slightly different. This can be observed even with aging membranes, which have many small sites, the OH ^" ions in

pass through to varying degrees. As already described above, this phenomenon can be clearly seen in FIG. At each startup now changes the individual profile of the voltage of each individual element a little, for example, by changing the membrane. Therefore, as a reference voltage for a comparison method, a theoretically expected voltage is unfavorable, since the individual influences such as diaphragm displacements or other changes that can cause other voltage profiles during each starting process are not taken into account. Tremblay et al. Describe in WO 2010/118533 A1 another possible method, wherein the current efficiency of each cell element is calculated at low Eiektrolyseströmen from the time-dependent voltage curve both when switching off the electrolysis system and when starting with the help of empirically determined cell parameters. In detail, the procedure provides for the following procedure:

Trigger is the low polarization current of about 20 to 50A, which is supplied to the cell elements in the chlor-alkali electrolysis to prevent after switching off the system that diffuse without electric field chlorate and Hypochloritionen to the cathode side and there the noble metal coating Dissolve the cathode, which ensures the lowest possible overvoltages in the cathodic hydrogen formation. With the effectiveness of the polarization current, 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 has been reached for each cell element. The current yield calculation of

Single elements then takes place via a function in which for each element whose specific time duration is used, which takes the element to after switching on the

Polarization current to reach this predetermined voltage value.

When you turn on the system, the triggering time is also defined by switching on the polarization current and thus the start-up so the startup of the system. The electrolysis current is now raised to a certain value and the time-dependent course of the individual element voltages observed. As in the case of switching off the

Electrolysis current is now determined the specific time for each individual element, which needs the single element voltage to reach a predefined voltage value. The current yield calculation of the individual elements then takes place via a function in which this element-specific time period until reaching the predetermined voltage value Switching on the polarization current is used.

This time function is provided by Tremblay et al. is defined as being based on an empirical model that takes into account a variety of electrolyzer properties in numerical simulations, such as the magnitude of the polarization current, the volume of the

Anode compartments, membrane area, brine volume flow, caustic concentration, pH, etc. An example of a function with five different parameters and logarithmic and exponential fractions is also presented. This approach has a number of disadvantages. In the case of switching off the electrolysis is a lot of free chlorine in the cell. This free chlorine captures the incoming OH ^' ions and reacts to hypochlorite and chlorate. The anolyte pH thus remains less than 7 in the acidic range and prevents the formation of oxygen which proceeds in the alkaline state. The chemical basis for a function of the method after switching off the system is thus given only conditionally.

The method also depends on that a polarization current is introduced. However, depending on the stability of the noble metals of the cathode coating to free chlorine, no polarization current is required and such is neither required during startup nor during shutdown, so that the process described so can not be performed.

When starting a polarization current with application of the electrolysis is not needed and thus sometimes created only after switching on the system and thus the electrolysis. Alternatively, the polarization current can be applied as early as 1-2 hours before the electrolysis current is switched on as part of the switch-on preparations. It is therefore not clear how to define the exact start time for the evaluation of the voltage profiles and what influence the definition of the start time has on the calculation function for the single element current efficiency. An empirical function with many different regression parameters, all via appropriate modeling and taking into account the

Electrolyzer properties such as cell design or physical conditions always leads to inaccuracies, since any change in a property that affects one or more regression parameters, the

Calculation basis of the empirical function changed. Changes in the Electrolysis system in the form of individual newly constructed cell elements in the electrolyser, or changed operating conditions, aging effects, etc., will thus be difficult to take into account and require mathematical adjustments. The choice of the individual time period to be determined for each cell element as a basic variable for the calculation of the individual element current yield leads to inaccuracies. Since the rate of current increase is not predetermined, the individual time until the voltage of each time element has reached the predetermined level will be different depending on whether the current is increased rapidly or slowly. It is questionable whether the resulting changes in the determination of the regression parameters are taken into account.

It is therefore an object of the invention to provide an alternative method for determining the current efficiency for individual elements of an electrolyzer consisting of at least one individual element available, the said disadvantages from the prior

Technology no longer has. 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 periods should be disregarded to achieve a given event. In addition, the method should make do without elaborate modeling for the determination of regression parameters and the method should do without the consideration of cell design and operating conditions.

This object is achieved with the features of claim 1. advantageous

Embodiments of the invention will become apparent from the dependent claims.

The invention provides that the current efficiency of the individual elements of a

Electrolysers, comprising at least one individual element, via a surface comparison, which can be performed at each startup of an electrolysis system for each element. For this purpose, the procedure is such that:

 a. an electrolysis I to an electrolyzer consisting of at least one

Single element i is applied and the electrolysis current I is raised to a certain current value I _E ND, where I _E ND is between 1 kA and 2.7 kA and in particular is between 1, 8kA and 2.2kA,

b. a time t _{0 is} determined, which arbitrarily before or after turning on the Electrolysis current is set, the electrolysis current a certain

Maximum value l ₀ , where l _{0 is} between 10A and 200A, the voltage Uj of the at least one individual element i is measured and the mean value of all individual element voltages U _{M is} formed,

the time t _EN o is determined, after all cell voltages U, the individual elements a defined voltage difference AU _END from the mean of all

Individual element voltages U _M differ, where AU _E ND is between 10mV and 200mV,

the area A, under the voltage curve Uj (x) of each individual element i is determined via numerical integration via the variable x in the boundaries between x ₀ = x (t ₀ ) and x _END = (t _E ND):

f. the area A _M under the voltage curve of the average of all individual elements U _M (x) is determined via numerical integration via the variable x in the limits x (t ₀ ) and x (t _END ):

G. the average electrolyzer flow _yield CE _{EL is} determined,

 H. the current efficiency CE, each individual element i depending on the

Elektrolyseurstromausbeute CE _{EL is} calculated via an empirical function f, which includes the area ratio A, / AM.

Core idea of the invention is therefore to derive the current efficiency of the individual elements empirically on a pure comparative consideration. According to the state of the art, the current efficiency of the electrolyzer, ie the average of all individual elements CE _EL , can be calculated via anodic or cathodic balances. The course of the average voltage U _{M of} all individual elements when starting up to a specific current level at which oxygen formation no longer takes place due to the resulting voltage and hence potential level or becomes negligible due to chlorine formation is thus to be interpreted as a measure of the average current efficiency CE _EL , Now the area under the

Determined voltage curve when applied against a suitable influence parameter between a defined start and end time, so this value AM is a measure of the anodic potential and thus the voltage-determining amount of liquor and thus the Current efficiency CE _EL .

If now the area under the voltage curve of each individual element is plotted against the appropriate influencing parameter to be selected, ie the variable x, and determined between the same start and end time as in the voltage average, this results in the formation of a quotient of element-specific area Aj on the area AM, a value that tends to show, for each individual element, how strong the leaching diffusion and thus the current efficiency compared to the average. Multiplication of the quotient with the mean current yield CE _E L thus leads to a measured value for the

Single element current yield CE ,.

Advantageously, the time t is used in an embodiment of the invention as a variable x. In an alternative embodiment, the electrolysis current I is used as variable x. In an embodiment of the invention, a cathodic balance is performed to determine the Elektrolyseurstromausbeute CE _EL by a supplied to the electrolyzer

Laugemenge and the leachate produced in the electrolyzer are circulated in a closed circuit between the electrolyzer and a Laugeauffangbehälter, the current load is kept constant for a certain period of time, the level of the Laugeauffangbehälters is kept constant by the produced leachate is discharged from the circuit, the Concentration and the volume flow of the produced leach quantity are measured, and the current efficiency for the given period of time according to equation (2) on the ratio of produced leachate is calculated to the theoretically possible Laugeproduktionsmenge dependent on the current load.

In an alternative embodiment, the determination of the

Elektrolyseurstromausbeute CE _E L carried out an anodic balance, wherein before and after the electrolysis in the brine C _Na2 so and in the anolyte C ' _Na2 so existing

Sodium sulfate concentration is measured, the ratio of the amount of sulfate in brine and anolyte is formed and the Anolytvolumenstrom V 'according to equation (3) is determined by multiplication with the measured brine flow V, then the concentrations of oxygen y ₀₂ and chlorine gas y _a2 in the product gas, the concentrations of sodium hydroxide _Na C oH, sodium chlorate C _Na cio, sodium carbonate and hydrochloric acid C _H ci in the brine, and the concentrations of sodium chlorate C _'Na2 so "hypochlorite and hydrochloric acid C'HOCI C'HCI in Anolytes are determined and the current efficiency of the Anolytkomponenten ηι are determined according to the equations (4) to (9) and finally the current efficiency CE summarily calculated via equation (10). In another alternative embodiment, the determination of the

Electrolyser current _yield CE _EL a simplified anodic balance according to the formula

CE _EL = P1 - (P2 / 1) x (Q _{A A} xd xc _A) + (0.5 - y _Q2) x P3 carried out, where I is the electrolysis current, Q _A, the power supplied to the cell element

Acid volume flow, d _{A is} the density of the acid, c _{A is} the mass concentration of the acid used, y ₀ 2 is the oxygen content in the anodic product gas, P1 is an empirically determined parameter, preferably between 98.5% and 99.5%, and in particular between 98, 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 and 9 , 0% and 3.0% and especially between 2.4% and 2.6%.

In a further alternative embodiment of the determination of

Electrolysis current efficiency CE _EL direct on-line measuring methods are used. These online measuring methods are known to the person skilled in the art.

Investigations have shown that the quotient Aj / A, however, is not directly proportional to the single element current yield. By selecting suitable sampling points on the individual element, the current efficiency can be determined analytically via the anodic balance. These results can be used as a basis to determine empirical fitting parameters. These parameters, as iteratively adapted as multiplier K1 or exponent K2, then lead to a very good agreement of the analytically determined current efficiency with the single element current yield determined via the voltage curve during startup, so that in one embodiment of the invention

method according to the invention the empirical function of the form

where 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 which is 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. [0036] Ein weiterer Vorteil des erfindungsgemäßen Verfahrens ist auch die Unabhängigkeit vom Polarisationsstrom und vom Faktor Individualzeit bis zum Erreichen eines bestimmten Spannungsniveaus, wie von Tremblay et. al. als notwendig beschrieben. Ob der Startzeitpunkt der Berechnung exakt beim Einschalten oder kurz vorher oder nachher gewählt wird, trägt zum Flächenvergleich nicht bei. Ob der Endzeitpunkt genau bei Erreichen eines spezifischen Spannungsniveaus oder einige Zeit später erreicht wird, ist ebenfalls ohne Bedeutung, da dieser Zeitfaktor beim Flächenvergleich keinen Einfluss hat. Insofern muss auch das Knowing the single element current yield CEj, an economic evaluation of each individual element can also be made via equation 1 by calculating the specific energy consumption in kWh / t product for each individual element of an electrolyzer from the single element voltage U, and the current efficiency CE, via the relationship

where F denotes a product-specific Faraday constant with the unit [t / kAh], which is formed by the quotient of molar Faraday constant and molecular weight of the product. Another advantage of the method according to the invention is also the independence of polarization current and the factor individual time to reach a certain voltage level, as of Tremblay et. al. described as necessary. Whether the starting time of the calculation is selected exactly at power-up or shortly before or after, does not contribute to the area comparison. Whether the end time is reached exactly on reaching a specific voltage level or some time later, is also irrelevant, since this time factor has no influence on the area comparison. In that sense, too

Presence of a polarization current can not be considered.

The surfaces can be determined in the simplest case by evaluating the voltage depending on the operating time t. Alternatively, the area calculation can also be in

Determine dependence on the electrolytic current I. Advantage of this approach is a complete independence of the speed with which the electrolysis current per unit time is increased until the target level of eg 2.5kA is reached. The determination of the areas when applied against the variable operating time t is shown in Fig.5. Since the areas can not be determined by classical mathematical integration, a numerical method must be used. Accordingly, from the start time t ₀ a fixed At is added and the voltages are determined at each time t and t + Δί both for each individual element and for the voltage average. The corresponding area can then be determined using the area equation for a trapezoid, ie (16) ΔΑ, (t) = 0.5 x (Ui (t) + U | (t + At)) X At

(17) AA _M (t) = 0.5 x (U _M (t) + U _M (t + At)) x At Summing all AA (t) between t ₀ and t _END then leads to the total area Ai,

the same applies to all AA _M (t) to AM.

For the electrolysis current as variable I, the calculation proceeds in the same way. Accordingly, starting from the starting time t _0, the electrolysis current I (t ₀ ) is selected as the starting value and a ΔΙ is added and the voltages for each I and Ι + ΔΙ 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, ie

(18) ΔΑ (Ι) = 0.5 x (U | (l) + Ui (l + Al)) x AI

(19) AA _M (I) = 0.5 x (U _M (I) + U _M (I + AI)) x Al

Sum up all AAi (l) between l ₀ and l _END then lead to the total area Ai,

the same applies to all AA _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 efficiency of the individual element deviates from the average current efficiency of all elements.

In one embodiment of the invention, four categories are provided here which are defined by absolute percent deviations from the average percentage current efficiency of all elements, whereby a category 1 is assigned to the individual elements that are at least 0.5%, preferably 1%, above the current yield average, Category 2 the individual elements are assigned, which are up to 2%, preferably up to 1% above or below the current yield average, a Category 3 the

Individual elements are assigned, which are at least 1%, preferably at least 2% below the current yield average of all elements and a category 4, the individual elements are assigned, at least 3% below the

Current yield average of all elements or have absolutely less than 90% current efficiency. Thus, individual elements of category 1 are therefore individual elements that are particularly good work, category 2 single elements that work in a normal dimension,

Single elements of category 3 represent below average working single elements and individual elements of category 4 are finally faulty elements. In a further option of the invention, the assignment of the elements into categories can be made via visual color representations. By way of example, the results of the assignments to category 1 in the color blue, assignments to category 2 in the color green, assignments to category 3 in the color yellow and assignments of the category 4 in the color red are shown.

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, which is in communication with the processor, and an execution element, which communicates with the processor and is configured to perform a method according to claim 1.

Particularly preferably, this system comprises a screen for receiving and displaying the data of the determination of the current efficiency of the individual elements of the

Used electrolyzer and to display the result of the determined current efficiency of the individual elements.

Such a system is shown by way of example in FIG. 7. The system 1 comprises an execution element 2, which is controlled by a processor 3, wherein the processor 3 is coupled to the data memory 4. An electrolyzer 5 is connected to the system 1 and comprises a plurality of individual element cells.

The data memory 4 is used to receive and store data required by the system 1 to determine the current efficiency of the individual elements of an electrolyzer according to the inventive method, which can be retrieved by the processor 3. The processor 3 and the data memory 4 are

commercially available and known in the art computer accessories, which is suitable for performing such operations. The execution element 2 is again constructed, for example, from several modules which receive the measured data of the individual elements of the electrolyzer 5 and charge according to the method according to claim 1, to deliver as a result the current yield of the individual elements to be determined. The above serve as a basis. The results are finally displayed on a screen 6 for each individual element.

Furthermore, the present invention comprises 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.

Advantages resulting from the invention:

Independence from the application of a polarization current

 Degrees of freedom at the start and end points for the evaluation

 No consideration of element specific, individual time periods for

Reaching a given event

 No consideration of complex modeling for the determination of

 regression parameters

No consideration of cell design and operating conditions

[0049] Drawings:

Fig. 1 is a graphic representation of the electrode potentials depending on the electrolysis current and the corresponding electrochemical partial reactions

Fig. 2 is a graphical representation of the electrode potentials when using a

 Anodencoatings to the effect on the change of the potential courses for

Clarify oxygen formation and chlorine formation

Fig. 3 is a graphic representation of the pH dependence of the potential profile of

 anodic oxygenation

Fig. 4 Typical voltage waveforms of the individual elements and the electrolysis when starting an electrolyzer

Fig.5 Diagram for the basic representation of the area determination of voltages as a function of the operating time t

FIG. 6 Diagram for the basic representation of the surface area determination of voltages as a function of the electrolytic current I

Fig. 7 Schematic representation of a system according to the invention for determining the current efficiency of the individual elements of an electrolyzer according to the inventive method

[0050] Symbols:

Symbol Meaning Unit i Subarea under the voltage curve of the individual element [-]

ΔΑ _Μ partial area under the average voltage curve [-]

 At time interval [s]

ΔΙ current change [kA]

AU Voltage change M

 AU | Voltage difference element i to the mean value M

 , Individual current yield of a component i [%]

 Ai area under the voltage curve of the single element [-]

A _M area under the voltage curve of the electrolyzer [-]

CA mass concentration of the acid [kg / kg]

Ci concentration of a component i in the brine [g / l]

Ci "concentration of a component i in the anolyte [g / i]

CE current efficiency [%]

CE _EL Average current yield of all individual elements [%]

CE | Current efficiency of single element [%] d _A Hydrochloric acid density [kg / i]

EV specific energy consumption [kWh / t]

EVi specific energy consumption of the single element [kWh / t]

F specific Faraday constant [t / kAh]

1 electrolysis current [kA]

K1 empirical parameter [-]

 K2 empirical parameter H

 Mp practically formed amount of product [kg]

M _T theoretically possible product quantity [kg]

P1 parameters [%]

 P2 parameters [% kg / kAh]

P3 parameters [%]

^Q A acid volume flow [l / h] t time [s]

U voltage M

 Ui single element voltage M

U _M Average stress of all individual elements M V brine flow rate [m ³ / h]

V 'anolyte volume flow [m ³ / h] x variable [-] y _C i2 chlorine content in the product gas [-] yo2 oxygen content in the product gas [-]

sign list system

Execution element processor

Data storage electrolyzer screen

Claims

claims: 1. A method for determining the current efficiency of the individual elements of an electrolyzer comprising at least one cell element of an electrolyzer  characterized in that  a. an electrolysis I to an electrolyzer consisting of at least one Single element is applied and the electrolysis current I is raised to a certain current value I _E ND, where I _E ND is between 1 kA and 2.7 kA and in particular between 1, 8 kA and 2.2 kA, b. a time t _{0 is} determined, which arbitrarily before or after turning on the  Electrolysis current is set, the electrolysis current a certain Maximum value l ₀ , where l _{0 is} between 10A and 200A, c. the voltage Ui of the at least one individual element is measured and the Mean value of all individual element voltages U _{M is} formed, d. the time t _E ND is determined, after all cell voltages U, the individual elements i a defined voltage difference AU _E ND from the average of all Individual element voltages U _M differ, where AU _EN D is between 10mV and 200mV, e. the area A, under the voltage curve U, (x) of each individual element i is determined by numerical integration via the variable x in the boundaries between x ₀ = x (t ₀ ) and x _END = XED):

f. the area A _M under the voltage curve of the average of all individual elements U _M (x) is determined by numerical integration via the variable x in the limits x (t ₀ ) and x (t _EN D):

G. the average electrolyzer flow _yield CE _{EL is} determined, and  H. the current efficiency CE, each individual element i depending on the Elektrolyseurstromausbeute CE _{EL is} calculated via an empirical function f, which includes the area ratio A, / A _M. 2. The method according to claim 1 characterized in that as variable x the time t is used. 3. The method according to claim 1 characterized in that as variable x the electrolysis current I is used. 4. The method according to any one of the preceding claims characterized in that to determine the Elektrolyseurstromausbeute CE _EL a cathodic balance is performed, wherein a leachate supplied to the electrolyzer and a leachate produced in the electrolyzer are circulated in a closed circuit between the electrolyzer and a Laugeauffangbehälter, the current load is kept constant for a certain period of time, the level the Laugeauffangbehälters is kept constant by the produced leachate is discharged from the circulation, the Concentration and the volume flow of produced leachate are measured during the discharge, and the current efficiency CE _EL for the given period of time according to the equation

is calculated via the ratio of produced leaching quantity M _P to theoretically possible lye production quantity M _T , which depends on the electricity load. 5. The method according to any one of claims 1 to 3 characterized in that for the determination of the electrolyzer _{effluent yield} CE _EL an anodic balance is carried out, whereby the sodium sulphate _{concentration} thus present in the brine C _Na2 and in the anolyte C ' _Na2 is measured before and after the electrolysis, the ratio of the sulphate quantity in Sole and anolyte is formed and the Anolytvolumenstrom V 'according to the equation

is determined by multiplication with the measured brine volume flow V, then the concentrations of oxygen v ₀₂ and chlorine gas ν _α2 in the product gas, the concentrations of sodium hydroxide C _NA0 H, sodium chlorate C _Na ci03 _> sodium carbonate C _Na2 co3 and hydrochloric acid C _H ci in the brine, and the concentrations of sodium chlorate C '^ so', hypochlorite C'HOCI and hydrochloric acid C'HCI in the anolyte are determined and the current yields of the anolyte components η are determined according to the following equations:

 C -V '  1 - 100% H ^Oa n - 7 - 0.980

I Alkali ^" - s ^Q L 100%  / i - 7 - 1.4923 = ^ C co, - V _{100O / o} « ^• 7 1.978 and finally the current efficiency CE _E _ is calculated summarily by the following equation: CE _EL = 100% - ^ _θ2 - T _NaC lo, ^{~ T} J 1 ^{~ T} 1 ^{+ T} lNa ^{+ T} 1 Alkali 6. The method according to any one of claims 1 to 3 characterized in that to determine the electrolyzer effluent _yield CE _EL a simplified anodic balance according to the formula CE _EL = P1 - (P2 / 1) x (Q _A xd _A xc _A ) + (0.5 - y ₀₂ ) x P3, where I is the electrolysis current, Q _{A is applied} to the cell element Acid volume flow, d _{A is} the density of the acid, c _{A is} the mass concentration of the acid used, y _{02 is} the oxygen content in the anodic product gas, P 1 is an empirically determined parameter, preferably between 98.5% and 99.5%, and especially between 98.9% and 99.1%, P2 is an empirically determined parameter which is preferably between 0.05 and 0.10% and more preferably between 0.07 and 0.09% and P3 is an empirically determined parameter, preferably between 2.0% and 3.0% and in particular between 2.4% and 2.6%. 7. The method according to any one of claims 1 to 3 characterized in that for determining the electrolyzer effluent yield CE _E L direct on-line measuring methods are used. 8. The method according to any one of the preceding claims, characterized in that the empirical function the form

where K1 is an empirical parameter, preferably between 0.8 and 1.2, and more particularly 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. 9. The method according to any one of the preceding claims, characterized in that a calculation of the specific energy consumption in kWh / t product for each individual element of an electrolyzer from the single element voltage U, and the current efficiency CE, on the context

where F denotes a product-specific Faraday constant with the unit [t / kAh], which is formed by the quotient of molar Faraday constant and molecular weight of the product. 10. The method according to any one of the preceding claims, characterized in that the cell elements are categorized into groups, depending on the amount Current efficiency of the single element CEj from the average current efficiency of all Elements CE _EL deviates. 11. The method according to claim 10 characterized in that the cell elements are divided into 4 categories defined by absolute percent deviations from the average percentage current efficiency of all elements, assigning to a category 1 those individual elements that are at least 0.5%, preferably 1% above the current yield average, a category 2 those individual elements , which are up to 2%, preferably up to 1% above or below the current yield average, are assigned to a category 3 those individual elements which are at least 1%, preferably at least 2% below the Current yield average of all elements and a category 4 are those Individual elements that are at least 3% below the Current yield average of all elements or have absolutely less than 90% current efficiency. 12. The method according to claim 11 characterized in that the assignment of the elements into categories takes place via visual color representations. 13. System for determining the current efficiency of the individual elements of an electrolyzer, comprising:  a processor in a computer system,  a data memory associated with the processor,  an execution element associated with the processor and configured to perform a method according to claim 1. 14. System according to claim 13 comprising a screen for receiving and displaying the data used to determine the current efficiency of the individual elements of the electrolyzer. 15. 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.