Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/02—Process control or regulation
  • C25B15/023—Measuring, analysing or testing during electrolytic production
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/02—Process control or regulation
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
  • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes

Definitions

• the present invention relates to a method for regulating an electrolysis cell. It is applied, for example, to the electrolysis of aqueous solutions of sodium chloride, which is the only industrial process, to produce chlorine and soda.
• Electrolysis is a process used industrially to produce, for example, alkali metal chlorates or alkali metal hydroxides.
• the electrolysis of sodium chloride solutions to produce chlorine and soda is the most important by the tonnages produced and because it is the only industrial process used today, see for example KIRK-OTHMER, Encyclopedia of Chemical Technology , 3rd edition, pages 799 to 865.
• This type of regulation uses at least one regulation loop and has drawbacks which result from the fact that the values of the parameters supplied by the sensors are approximate values of these characteristic parameters and not of very exact values.
• a regulating device operating directly from the parameter values characteristics provided by sensors does not make it possible to obtain an optimum regulation setpoint for an electrolysis cell to operate with optimum efficiency.
• US Patent 4,035,268 provides a device for adjusting the spacing of the electrodes in a cell of a process called "mercury”.
• European patent EP 99795 describes a system for regulating the intensity of a set of electrolysis cells. As before, these devices are only improved conventional regulations, that is to say that a parameter has been analyzed and more finely measured and that it has been sent to a conventional regulator.
• the object of the invention is to remedy the drawbacks of known devices for regulating the operation of an electrolysis cell, in particular by taking into account the values of a large number of parameters, and by corrective calculation of the values of these parameters, so as to allow regulation of the operation of the installation at maximum efficiency.
• This corrective calculation is in fact a consistency calculation of the values of the parameters measured.
• electrolysis cell also denotes a set of electrolysis cells.
• input product any flow of material which enters the cell, for example sodium chloride solution.
• an output product designates a flow of material leaving the cell, for example it is the sodium hydroxide and sodium chloride solution from a diaphragm process, or the sodium hydroxide solutions and the depleted sodium chloride solutions. membrane and mercury processes.
• the gas stream essentially formed of hydrogen is also an output from a chlorine / soda electrolysis cell.
• the measuring means (a) represent any usual system for measuring a gas or liquid flow rate such as a diaphragm, a venturi, a counter for example. All these systems deliver a signal representing the flow rate, the signal can be in electrical form such as a voltage or an intensity and be either analog or digital, or also in radioelectric form. It can also be a pneumatic signal that can be converted into an electrical signal.
• the regulating means (b) are for example means which act by variation of the pressure drop of an input or output product.
• pneumatic valves or solenoid valves are used.
• Variable speed pumps can also be used.
• the means (c) for measuring the temperature of the electrolyte are means known in themselves, they can be located in the cell near the electrodes or on a tube through which the electrolyte passes into or out of the cell. Like the means (a), they deliver signals, most often electrical, representing the temperature.
• the means for regulating the temperature of the electrolyte can be chosen from the means known per se for heat exchange, it is also possible to act on the temperature of the electrolyte entering the cell using these means. .
• the calculation means (d) are also means known per se and comprising for example electronic analog or digital or analog and digital calculation circuits and which are connected to the measurement means (a) and (c) by conventional links.
• the calculation means (d) are preferably computer type devices capable of performing digital and logical operations according to prerecorded instructions and according to prerecorded values and values or information transmitted by the measuring means (a) and (c) .
• These calculation means (d) are preferably supplemented by display means such as screens or printers and means for storing the information such as magnetic means.
• the cell intensity designates the electrical intensity that is measured between the electrodes or for example between the anodes and the mercury bed in the case of a mercury cell.
• "Intensity” also means the intensity of a set of cells.
• the intensity measurement means are the usual means used by electricians, as well as the means for regulating this intensity. To regulate the intensity, it is possible for example to use an action on the voltage of the diodes, of the rectifier or rectifiers or also on the starting angle of the thyristors of the rectifiers.
• the measurement means can also be confused with the regulation means.
• the intensity measurement means like the means (a) and (c) deliver signals representing this intensity. These analog or digital signals are preferably electrical in nature.
• the intensity measurement means are connected to the calculation means (d). These connections are most often materialized by cables conducting electricity, but it would not depart from the scope of the invention to use links by radio waves or infrared.
• the intensity measurement, the measurement (s) provided by the means (a) and the temperature measurement (s) supplied by the means (c) are connected to the calculation means (d) which carry out consistency processing of these measurements; that is to say that the means of calculation (d) using mathematical methods and the laws of physics and chemistry which apply to electrolysis, compare these measurements with each other, correll them by even partial assessment of the electrolysis cell, and determine the most probable values of the measured values and of the other values which are not measured and which are deduced by calculation, and can thus provide an improved signal (by these means calculation (d)) and applicable to the means of regulation, either of one of the flow rates, or of the intensity, or of the temperature of the electrolyte.
• the computing means (d) perform coherence treatments. The principle of coherence processing will be explained in detail below.
• the flow rate of one of the inlet or outlet products one can choose for example in chlorine / soda electrolysis, the flow of brine or the flow of water, or the soda flow. It is also essential to measure the temperature of the electrolyte as well as the electric intensity, then all these measures are coherent possibly by connecting them by physico-chemical relationships which they must respect for example the quantity of hydrogen produced can be connected to the intensity.
• the calculation means (d) provide at least one regulation signal applicable to the regulation means of the intensity or of one of the input or output products, or of the temperature. You can choose to regulate an input or output product different from the one whose measurement was used for the consistency calculation. For example, the flow of hydrogen leaving the cell, the temperature of the electrolyte and the intensity are used in the calculation means to deliver a signal applicable to the regulation of the flow of the solution to be electrolyzed.
• the calculation means (d) supply, in parallel with the signal applicable to the regulation, the coherent values of the flow rates and of the intensity. It is thus possible to know perfectly the operating conditions of the electrolysis cell.
• the signal or signals applicable to the regulation means in fact represent the set points of the various regulators. These signals representing values of flow rate, temperature or intensity result from the calculation of coherence and from one or more criteria which are set, such as by example maximum production, or such value of the intensity not to be exceeded, etc. It is thus possible, in view of the coherent assessment resulting from the coherence calculation and according to different criteria, to act on the regulator or regulators, that is to say - say that you manually modify the set point of the regulator (s).
• the flow meter A has a turbine sensor and the flow meter B has a pressure port sensor for example.
• For flowmeter B the value m B 105
• the manufacturer of the device A indicates that he carried out, on the flow M, a series of n experiments which gave him a set W A of measurements of M.
• the set W A has a normal distribution law, that is to say that the probability density of the law is, in known manner:
• the manufacturer of the device B indicates that he too has carried out a series of n experiments on the flow M and that he has obtained the set W B of the measurements of M.
• This set also has a probability density:
• the probability of obtaining a value m ′ A as close as possible to the value m A has the expression: where dm is the differential element of the variable m.
• the probability of achieving a value m ′ B as close as possible to the value m B has the expression:
• the probability of obtaining simultaneously in the sets W A and W B , the values m A and m B is maximum when the term: is minimum.
• the most probable value (and not certainly the closest value) of M is equal to 101.
• the certainty of obtaining values m closer to the true value than are the raw values m is obtained by multiplying the readings of raw measurements and their processing.
• the reduction of the error is 50% for measurement A and 66% for measurement B in the case where the true value is equal to 102, and the residual error of B then changes direction.
• the effectiveness of the treatment increases with the number of redundancies of the raw measurements and with the number of repeated treatments and also with the precision and / or the absolute errors of the measurements.
• the consistency calculation can be extended to any number of raw measurements subject to a certain number of constraints, provided of course that the number of constraints is less than the number of measurements.
• the consistency calculation takes into account, for example, the conservation of atoms in a chemical reaction, the conservation of the enthalpy balance, the conservation of electrons, charges or the electrochemical balance.
• the signal improved by the coherence processing is applied directly to at least one of the elements of the group constituted by the means (b) for regulating the flow rates, a means for regulating the intensity and the temperature regulation means.
• This connection is made by the same means as for example the connection of the measurement means (a) and of the calculation means (d), these are analog, digital, electrical or pneumatic connections, or a mixture of these techniques for example function distances and signal strengths necessary to attack the regulators.
• the calculation means (d) are not all applied directly to the regulation means. For example, one can have direct regulation of an input flow and a signal applicable to the electrolyte inlet temperature, the set point of this electrolyte inlet temperature is therefore manually changed.
• the electrolysis cell may comprise measuring means (e) providing signals for measuring the contents of at least one of the products chosen from the input products and the output products and these signals are connected to the calculation means (d).
• contents is meant the concentrations in the case of a liquid phase or the pH or the concentration or partial pressure in the case of a gaseous phase. It is not necessary to measure all the concentrations of an input or output product, it suffices for example in chlorine / soda electrolysis, to know the oxygen content in the chlorine at output. This measurement, in addition to the previous measurements, that is to say the flow rate of one of the input or output products, the temperature of the electrolyte and the intensity makes it possible to improve the consistency. According to another preferred form of the invention, it is possible to measure the contents of other input and output products or several contents of one of the products and only one content of another product. For example in the case of chlorine-soda electrolysis, it is preferred to measure the oxygen in the chlorine, and both the soda and the chloride in the product leaving the cell.
• the calculation means (d) can also provide one or more signals improved by the consistency processing and applicable to means for controlling an element of the content of a product of entry or exit.
• the content of the input product in the compound to be electrolyzed can be modified by adding a diluent or pure product to be electrolyzed to increase the content. So for example, in the electrolysis of sodium chloride one can add sodium chloride in the input product to increase the chloride concentration or add water to lower this concentration, one can also modify its ph.
• the means (d) can also provide applicable signals and directly applied signals.
• the cell can comprise means for measuring (f) at least one parameter chosen from pressure and temperature, said parameter belonging to at least one of the elements of the group consisting of the input products, the output products and the compartments of the cell, and in that these measurement means (f) are connected to the calculation means (d).
• the cell can comprise means for regulating (g) at least one parameter chosen from pressure and temperature, said parameter belonging to at least one of the elements of the group constituted by the products input, output products.
• These calculation means (d) provide regulation signals, some applicable to the regulation means (g), others applied directly to the means (g).
• the pressure or the temperature which one regulates by a signal resulting from the means of calculation (d), can be that which one measured or another. This is how we can, for example, measure the temperature of the input product to be electrolyzed, take this measurement into account in the coherence calculation and regulate with a signal improved by the coherence calculation and coming from the calculation means. the pressure of a gas from one of the electrodes.
• the present invention is particularly useful in chlorine-soda electrolysis.
• the present invention is more particularly useful in the case of the membrane electrolysis process, the flow of hydrogen being able to be connected directly to the flow of electrons.
• the means of calculation also provide the intermediate stages of the calculations and especially the most probable values that we can therefore compare with the measured values. Their difference is expressed as a correction coefficient.
• the permanent display of these correction coefficients makes it possible to manage the operation of the cell (or of a set of cells) while retaining control of the process.
• Another advantage of the invention appears here, namely that it is possible, by consulting the relative deviations, to find which measurement is faulty and must be repaired.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
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• Organic Chemistry (AREA)
• Automation & Control Theory (AREA)
• Analytical Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)
• Apparatus Associated With Microorganisms And Enzymes (AREA)
• Immobilizing And Processing Of Enzymes And Microorganisms (AREA)
• Electrolytic Production Of Metals (AREA)
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• Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
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• 1988
  • 1988-03-17 FR FR8803446A patent/FR2628757B1/fr not_active Expired - Lifetime
• 1989
  • 1989-03-01 NO NO890863A patent/NO176725C/no unknown
  • 1989-03-07 ES ES89400637T patent/ES2043050T3/es not_active Expired - Lifetime
  • 1989-03-07 DE DE89400637T patent/DE68907094T2/de not_active Expired - Fee Related
  • 1989-03-07 EP EP89400637A patent/EP0333556B1/fr not_active Expired - Lifetime
  • 1989-03-07 AT AT89400637T patent/ATE90740T1/de not_active IP Right Cessation
  • 1989-03-16 FI FI891255A patent/FI89187C/fi not_active IP Right Cessation
  • 1989-03-16 IE IE86189A patent/IE63495B1/en not_active IP Right Cessation
  • 1989-03-16 DK DK198901278A patent/DK174442B1/da not_active IP Right Cessation
  • 1989-03-16 PT PT90024A patent/PT90024B/pt not_active IP Right Cessation
  • 1989-03-16 CA CA000593994A patent/CA1316486C/fr not_active Expired - Fee Related
  • 1989-03-17 JP JP8965787A patent/JPH01294885A/ja active Pending
  • 1989-03-17 US US07/324,822 patent/US4952298A/en not_active Expired - Lifetime
  • 1989-03-17 KR KR1019890003357A patent/KR930006342B1/ko not_active IP Right Cessation
  • 1989-03-17 CN CN89101436A patent/CN1093178C/zh not_active Expired - Fee Related

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