EP3266904B1 - Molten salt electrolysis system and control method for operation of the same - Google Patents

Molten salt electrolysis system and control method for operation of the same Download PDF

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Publication number
EP3266904B1
EP3266904B1 EP16177980.6A EP16177980A EP3266904B1 EP 3266904 B1 EP3266904 B1 EP 3266904B1 EP 16177980 A EP16177980 A EP 16177980A EP 3266904 B1 EP3266904 B1 EP 3266904B1
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cell
molten salt
salt electrolysis
heat
electrolysis cell
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German (de)
French (fr)
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EP3266904A1 (en
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Roman Düssel
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Trimet Aluminium SE
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Trimet Aluminium SE
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/20—Automatic control or regulation of cells
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/06—Operating or servicing

Definitions

  • the present invention relates to a control method for operating a cell of a melt flow electrolysis system, in particular for the production of aluminum.
  • the present invention also relates to a melt-flow electrolysis system, in particular for the production of aluminum, with a melt-flow electrolysis cell.
  • the regeneratively provided energy cannot be stored due to storage media that have not yet been available to a suitable extent and can then be accessed depending on the electricity demand. Furthermore, the regenerative energy can only be fed into the power grid if the corresponding energy sources, in particular the volatile energy sources from wind and sun, enable the conversion into electrical energy and its feeding into the power grid.
  • the consumers in the power grid would therefore have to adapt their electrical energy requirements as far as possible to the feed-in from regenerative energy sources, provided that fossil energy sources are not used as a buffer.
  • Industries that have a very high energy requirement are particularly affected by this trend, because their electricity consumption does not fit in with the general electricity requirement and can therefore hardly be compensated for by other electricity consumers. This includes, in particular, aluminum production, but other branches of industry, particularly those in the chemical industry, are also heavily affected by this development.
  • fused flux electrolysis processes are therefore control processes in the control engineering sense, which can rely on constant, very easily predeterminable boundary conditions.
  • the temperature of the melt inside the melt flow electrolysis cell is determined at relatively long intervals, for example once a day.
  • the solidification temperature is also determined at relatively long intervals, for example after the temperature of the melt has been determined.
  • Another approach is based on the determination of the AlF 3 content of the melt.
  • the thickness of the crust is kept within a practicable range by adapting the voltage drop across the fused salt electrolysis cell, if necessary. For example, in the case of a fused metal electrolysis cell, it is assumed that the crust has a suitable thickness if the temperature of the melt is 8 ° C. above its solidification temperature.
  • Out DE 26 15 652 A1 describes a method for measuring and controlling the energy balance of aluminum furnaces, in which the immersion depth of the anode of the electrolytic cell is changed as a function of a temperature measured in the furnace lining on the side.
  • GB 2 076 428 A discloses a method for operating an aluminum electrolysis cell in which a heat dissipation through heat pipes is controlled as a function of a measured cell wall temperature.
  • CH 648 871 A5 describes a method for checking the board in a fused-salt electrolysis cell, in which the immersion depth of the anode is changed depending on the energy supplied, taking into account the current strength and the ohmic bath resistance.
  • melt flow electrolysis system in which the melt flow electrolysis system is controlled in such a way that the amount of electrical power it consumes is adapted to the amount of electrical power simultaneously fed in by a volatile energy source.
  • the melt flow electrolysis system can be used as a "virtual battery" in the Use power grid.
  • the power consumption of the melt flow electrolysis system is adjusted, within the system limits of the system, to the amount of energy available in the power grid by means of a corresponding control of the power consumption.
  • the present invention has the object of providing a method for operating a cell of a melt-flow electrolysis system, in particular for the production of aluminum, as well as a melt-flow electrolysis system, in particular for the production of aluminum, with a corresponding melt-flow electrolysis cell, whereby an economical and process-reliable Production process when operating the melt flow electrolysis system is also possible under the prerequisite of fluctuating availability of electrical energy in the power grid.
  • An object of the present invention is to provide a control method and a melt-flow electrolysis system of the technical field described above, whereby the melt-flow electrolysis can be operated safely with variable availability of electrical energy, in particular without additional loading of the melt-flow electrolysis cells or the efficiency of the melt-flow electrolysis, in particular the production of Aluminum.
  • a control method according to the invention is defined in claim 1.
  • a melt flow electrolysis system according to the invention results from claim 8.
  • a use according to the invention of the control method or the melt flow electrolysis system results from claim 14.
  • the control method according to the invention for operating a cell of a melt flow electrolysis system, in particular for the production of aluminum is characterized in that a first control variable is an energy balance of the cell, which takes into account the electrical energy entering the melt flow electrolysis cell and the thermal energy exiting the melt flow electrolysis cell, with a second
  • the controlled variable is a thermal state of the cell.
  • “regulation” or “regulation” is understood to mean a process in which a variable, the “controlled variable”, is continuously recorded, compared with another variable, the “reference variable”, and in the sense of an approximation to the Reference variable is influenced.
  • the closed action sequence, in which the controlled variable continuously influences itself in the action path of the control loop, is characteristic of the control.
  • “regulation” or “regulation” is also understood to mean a process in which the “controlled variable” is continuously simulated instead of measured, compared with the “reference variable” and influenced in the sense of an adjustment to the reference variable. With this form of control in the present sense, too, the closed action sequence, in which the controlled variable continuously influences itself in the action path of the control loop, is characteristic.
  • direct or indirect measurement of the heat output can be dispensed with and this can instead be determined on the basis of a simulation of the heat output.
  • the previous mode of operation must be deviated from.
  • the operation of the Melt-flow electrolysis cell regulated in such a way that the electrolyte temperature is in a relatively wide temperature range. According to the invention, this is brought about by the control-related consideration of the heat balance.
  • the heat balance is understood to mean an energy balance which takes into account the electrical energy entering the fused electrolysis cell and the thermal energy exiting the fused electrolysis cell.
  • the proportion of the electrical energy entering the aluminum electrolysis cell used for the production of aluminum is also preferably determined.
  • this proportion of the electrical energy entering the aluminum electrolysis cell can be assumed to be constant and the proportion introduced as heat into the aluminum electrolysis cell can be determined from the difference between the total electrical energy and the energy used for production, which is assumed to be constant.
  • the heat balance of the fused flux electrolysis cell is consequently determined and the operation of the fused flow electrolysis cell is regulated on the basis of the heat balance as a control variable.
  • a thermocouple and / or a device, in particular a measuring device, for determining a volume flow of exhaust air from the cell and / or a device, in particular a measuring device, for determining a volume flow of a heat transport fluid in a heat exchanger on the cell is or are preferred as a measuring element or several measuring elements are used to determine the first controlled variable, ie the heat balance.
  • At least 6, preferably at least 12, more preferably at least 30, more preferably at least are preferred 60, thermocouples arranged on the cell in order to be able to determine the temperature distribution on the cell and thus also the heat balance as precisely as possible.
  • melt flow electrolysis cells of a melt flow electrolysis system are provided with the thermocouple or the multiple thermocouples. This simplifies the design effort of the overall system and largely achieves the desired goal of the regulated operation of the melt flow electrolysis system.
  • thermocouples can function individually or jointly as a measuring element in the control engineering sense. This basically also applies to the device for determining the volume flow of the exhaust air from the cell, which can determine the mass flow as an alternative or in addition to the volume flow and can preferably also determine information on the temperature of the exhaust air.
  • Such a device for determining the volume flow of the exhaust air from the cell or the device for determining a volume flow of the heat transfer fluid in the heat exchanger can also function, for example, by determining a speed of a fan or a corresponding element, also indirectly, for example via the energy consumption or the (Rotary) field of an electric motor driving the fan. In this way it is possible to determine the volume flow of exhaust air or heat transport fluid without measuring it directly, because the volume flow is generated at least to a substantial extent by the fan or a corresponding element. Nevertheless, this determination of the volume flow in the Regulation of the operation of the fused metal electrolysis cell can be processed as "measurement".
  • Said heat transfer fluid can in particular be air, which can be guided along the cell wall, for example, in a basically known heat exchanger.
  • the heat transport fluid in addition to the volume flow or instead of the volume flow, a mass flow can also be determined, and the temperature of the heat transport fluid can also preferably be determined.
  • the heat exchanger can influence the extent of cooling or heat loss of the fused-salt electrolysis cell and thus in particular the thickness of the crust along its edge and thus influence the heat balance in several ways.
  • thermocouple devices for determining a volume flow of an exhaust air from the cell and measuring device for determining a volume flow of a heat transfer fluid in a heat exchanger on the cell, for continuous detection of a heat supplied to the cell and a heat dissipated from the cell Heat suitable and designed.
  • the cell has side walls, a floor and an exhaust air duct, with arranged on or in at least one of the side walls, the floor or the exhaust air duct, preferably on or in all side walls and the floor and particularly preferably also on or in the exhaust air duct
  • Thermocouples are used as measuring elements to determine the heat balance.
  • At least one heat exchanger and / or at least one exhaust gas flow flap and / or a chemical composition of the melt, in particular an AlF 3 metering, and / or at least one crossbeam for positioning at least one anode in the cell as an actuator to act on a heat input and / or are preferred a heat discharge is used.
  • the above-mentioned elements make it possible to vary the heat input and / or heat output within relatively wide limits, the heat input or heat output being used as a manipulated variable when regulating the heat balance. In principle, there are also other ways of varying the heat input or heat output, but the above-mentioned elements have proven to be particularly effective in connection with fused-salt electrolysis cells.
  • a corresponding adjustment of the voltage drop across the fused-melt electrolysis cell is carried out. This can be brought about in particular by changing the distance between the anode or a plurality of anodes and the cathode or a plurality of cathodes.
  • An increase in the current basically brings more heat into the fused-salt electrolysis cell, while a reduction in the voltage, ie a reduction in the distance between the electrodes, leads to a fundamentally lower heat input.
  • the position of the exhaust gas flow flap or heat exchanger is preferably used to further influence the heat output from the fused salt electrolysis cell taken because the variation of the heat input is possible more effectively than that of the heat output.
  • An entry of material to be melted, in particular aluminum oxide and cryolite, and / or a discharge of molten material, in particular aluminum, and / or a change in a melt flow electrolysis current strength are also taken into account as a disturbance variable.
  • the entry of material to be melted changes not only the temperature of the electrolyte bath, but also its chemical composition, which has an impact on the heat balance of the operation of the melt flow electrolysis cell.
  • the melt flow electrolysis current strength changes the energy input and thus the amount of heat supplied.
  • the strength of the current can vary in an uncontrolled manner within certain limits, in particular due to the variable energy present in the power network and thus bypassing the regulation of the fused-salt electrolysis itself.
  • a third control variable is a chemical state of the cell.
  • the thermal state of the cell is to be understood in particular as the temperature of the electrolyte as a decisive variable.
  • other elements of the cell also contribute to its thermal Condition at.
  • the most critical part of the cell is the electrolyte, because its temperature must be kept above its solidification temperature in any case in order to keep the melt flow electrolysis system functional.
  • the chemical state of the cell is therefore also largely determined by the solidification temperature of the electrolyte, which depends in particular on the "AlF 3 excess".
  • a melt-flow electrolysis system according to the invention in particular for the production of aluminum, with a melt-flow electrolysis cell is characterized in that the melt-flow electrolysis system has a control device which is designed to carry out one of the control methods described above.
  • the melt flow electrolysis system comprises a thermocouple and / or a measuring device for determining a volume flow of exhaust air from the melt flow electrolysis cell and / or, if a heat exchanger for influencing a heat input or heat output by means of a heat transport fluid on at least one outer surface of the melt flow electrolysis cell is included, a measuring device for determination a volume flow rate of the heat transport fluid in the heat exchanger at the fused salt electrolysis cell.
  • these elements are particularly well suited to be used as measuring elements in the inventive control, because they provide meaningful information for determining the heat balance of the fused metal electrolysis cell and therefore allow the control to be implemented particularly easily.
  • the melt flow electrolysis cell of a preferred melt flow electrolysis system has side walls, a base and an exhaust air duct, with thermocouples on or in at least one of the side walls, the base or the exhaust air duct, preferably on or in all side walls and the base and particularly preferably also on or in the exhaust air duct are arranged. This makes it possible to determine the heat balance of the fusible flow electrolysis cell particularly well and is therefore particularly suitable for use in the context of the invention.
  • the melt flow electrolysis system comprises a heat exchanger for influencing a heat input or heat output by means of a heat transport fluid on at least one outer surface of the melt flow electrolysis cell and / or an adjustable exhaust gas flow flap for influencing a volume flow of an exhaust gas from the melt flow electrolysis cell and / or a device for changing a chemical composition of the melt, in particular for changing a dosage of AlF 3 in the melt, and / or a cross member for positioning an anode in the melt flow electrolysis cell.
  • heat loss and heat input can be efficiently adjusted and varied within wide limits in order to adapt the heat balance as efficiently as possible to its setpoint. There are basically other ways of influencing the heat balance, but they are less effective and therefore inefficient.
  • a preferred melt-flow electrolysis system comprises a device for determining a mass of material to be melted introduced into the melt-flow electrolysis cell, in particular aluminum oxide and cryolite, and / or a device for determining a mass of molten material removed from the melt-flow electrolysis cell, in particular aluminum.
  • the material introduced into the cell and removed from the cell not only changes the heat balance in that heat is removed from or brought into the fused metal electrolysis cell system, but also partially changes the chemical composition of the contents of the cell Fused metal electrolysis cell, which has an influence in particular on the solidification temperature of the electrolyte and should therefore be taken into account when regulating the heat balance.
  • the change in the temperature of the material in the cell also has an influence on the chemical composition of the melt due to the change in the thickness of the edge crust caused by this.
  • An increase in temperature leads to further melting of the crust and thus a reduction in the proportion of AlF 3 in the melt. Since this last-mentioned process exhibits a certain inertia and pendulum motion, the determination of the chemical composition was error-prone shortly after the current intensity supplied to the cell was varied.
  • the control according to the invention can compensate for these errors and avoid misinterpretations.
  • the above-described control method or a melt-flow electrolysis system described above provided that the melt-flow electrolysis system is connected to a power grid in order to be supplied with electrical energy for the melt-flow electrolysis, in other words wherein a current used for operating the cell is supplied from the power grid, used to compensate for fluctuations in feeding energy into the power grid.
  • Such fluctuations lead to an imbalance between feed-in and consumption, which results in frequency deviations and / or voltage deviations in the network within a very short time, which endanger the stable operation of the network and must therefore be corrected immediately to avoid network breakdowns ("blackouts").
  • melt flow electrolysis system according to the invention or the control method for operating the melt flow electrolysis system are designed in such a way that the melt flow electrolysis system can be operated within the system limits with different consumption capacities the fused-salt electrolysis process can be used very well as a buffer to compensate for these power balance imbalances and thus to stabilize the grid.
  • Figure 1 shows a diagram of a preferred process management by means of closed real-time heat balance control.
  • the heat balance is used as the reference variable w (t).
  • a control deviation e (t) of the heat balance that is to say a deviation of the heat balance from the target value, is compensated for by a controller on the basis of a heat balance feedback y m (t).
  • the controller determines through the comparison between the reference variable w (t) and feedback y m (t) a deviation of the determined heat balance y (t) from the reference variable w (t) and determines appropriate countermeasures in order to adapt the controlled variable to the reference variable.
  • the heat loss or heat input are viewed as the general manipulated variable u (t).
  • the controller can, for example, influence a heat exchanger, exhaust gas flow dampers, the bath chemistry and the voltage inside the molten electrolysis cell.
  • the specific manipulated variable u S (t) which can be influenced by the controller, can, for example, be the flap position of exhaust gas flow flaps in an exhaust gas duct, a dosage of AlF 3 in the electrolyte bath, a flow rate of heat transfer fluid in the heat exchanger or a crossbar position, i.e.
  • the controlled system is therefore the fused metal electrolysis cell with its components such as the heat exchanger, the exhaust gas flow guide, the crossbeam, fan, flaps, etc.
  • the heat balance can be determined, for example, by thermocouples for measuring the temperatures on the side walls, the floor and the exhaust air duct as well as by elements for determining a volume flow of both the exhaust air and a heat transfer fluid possibly flowing through a heat exchanger in connection with an evaluation unit.
  • the data measured and evaluated by these measuring elements are fed to the controller in order to set the corresponding actuators appropriately.
  • the heat in the fused salt electrolysis cell is mainly generated in the area of the anode-cathode distance.
  • a reduction in the distance when the amperage increases and an increase in the distance when the amperage is reduced represents a first measure for regulating the heat balance. This varies the ohmic resistance of the fused-salt electrolysis cell, which is within certain limits, in particular due to a minimum distance between anode and aluminum pool as well as a energy-efficient processes are determined is possible.
  • an exhaust gas flow can be varied and in this way the heat balance of the fused-salt electrolysis cell can also be influenced.
  • An increase in the exhaust gas flow increases heat output, while a reduction in the exhaust gas flow acts as an insulation.
  • melt flow electrolysis system in particular an aluminum electrolysis system, without the requirement of a to operate a constant amperage made available from the power grid in an economically viable manner.
  • FIG. 12 shows a schematic view of a melt flow electrolysis system with a melt flow electrolysis cell 30.
  • the melt flow electrolysis cell 30 is laterally bounded by cell walls 32 and also has a cell bottom 34, which at the same time functions as a cathode for the melt flow electrolysis process inside the cell 30.
  • Inside the cell 30 there is an anode 36 protruding from above into the cell 30 and the melt 38, 35.1, which includes cryolite and molten aluminum, among other things.
  • a heat exchanger 39 is arranged through which a fluid, such as. B. air, CO 2 , nitrogen or a liquid is passed.
  • the heat exchanger 39 is particularly preferably connected via a line system 31 to a heat store 33, which can be formed, for example, by a conventional or also a latency heat store.
  • heat can be conducted from the heat store 33 through the line system 31 to the heat exchanger 39.
  • the inside of the fused metal electrolysis cell can be effectively heated via the cell walls 32 by less heat being radiated to the outside, because the temperature difference between the inside of the cell and the outside of the cell walls 32 is reduced, and the solidification of the melt is thereby inhibited.
  • the same effect is achieved by varying the exhaust gases sucked up or retained.
  • a control device 37 is designed to operate the cell of the melt flow electrolysis system in such a way that its heat balance is controlled, as has been described above.
  • the fusible electrolysis cell comprises a multiplicity of thermocouples (not shown) in its side walls, the bottom and also in the area of its exhaust air duct adjoining the fusible electrolysis cell at the top. The measurement results recorded by these thermocouples are fed to the regulating device 37 and evaluated there to regulate the operation of the melt-flow electrolysis cell.
  • the power grid can also be kept stable despite the infeed of volatile energy sources, without having to resort to special (currently insufficiently available) storage devices and the like.

Description

TECHNISCHES GEBIETTECHNICAL AREA

Die vorliegende Erfindung betrifft ein Regelungsverfahren zum Betreiben einer Zelle einer Schmelzflusselektrolyseanlage, insbesondere zur Herstellung von Aluminium. Ferner betrifft die vorliegende Erfindung eine Schmelzflusselektrolyseanlage, insbesondere zur Herstellung von Aluminium, mit einer Schmelzflusselektrolysezelle.The present invention relates to a control method for operating a cell of a melt flow electrolysis system, in particular for the production of aluminum. The present invention also relates to a melt-flow electrolysis system, in particular for the production of aluminum, with a melt-flow electrolysis cell.

STAND DER TECHNIKSTATE OF THE ART

In vielen Industrienationen der Welt wird geplant und zum Teil bereits umgesetzt, die Energieversorgung hin zu sogenannten regenerativen Energien zu verschieben, um die Erzeugung von möglicherweise klimaschädlichen Gasen wie CO2 deutlich zu reduzieren und um von fossilen Energieträgern zunehmend unabhängig zu werden.In many industrialized nations of the world there are plans and in some cases already implemented to shift the energy supply to so-called regenerative energies in order to significantly reduce the generation of potentially climate-damaging gases such as CO 2 and to become increasingly independent of fossil fuels.

Die regenerativ bereitgestellte Energie kann aufgrund bisher nicht in geeignetem Umfang verfügbarer Speichermedien nicht gespeichert und anschließend in Abhängigkeit des Strombedarfs abgerufen werden. Ferner kann die regenerative Energie nur dann in das Stromnetz eingespeist werden, wenn die entsprechenden Energiequellen, insbesondere die volatilen Energiequellen aus Wind und Sonne, die Umwandlung in elektrische Energie und deren Einspeisung in das Stromnetz ermöglichen. Die sich im Stromnetz befindlichen Abnehmer müssten also ihren elektrischen Energiebedarf weitestgehend an die Einspeisung durch regenerative Energieträger anpassen, soweit auf fossile Energieträger als Puffer verzichtet wird. Besonders betroffen von diesem Trend sind Industriezweige, die einen sehr hohen Energiebedarf haben, weil deren Stromabnahme sich nicht ohne weiteres in den allgemeinen Strombedarf einfügt und daher kaum durch andere Stromabnehmer ausgeglichen werden kann. Hierzu zählt insbesondere die Aluminiumherstellung, aber auch andere Industriezweige insbesondere aus der Chemieindustrie sind von dieser Entwicklung stark betroffen.The regeneratively provided energy cannot be stored due to storage media that have not yet been available to a suitable extent and can then be accessed depending on the electricity demand. Furthermore, the regenerative energy can only be fed into the power grid if the corresponding energy sources, in particular the volatile energy sources from wind and sun, enable the conversion into electrical energy and its feeding into the power grid. The consumers in the power grid would therefore have to adapt their electrical energy requirements as far as possible to the feed-in from regenerative energy sources, provided that fossil energy sources are not used as a buffer. Industries that have a very high energy requirement are particularly affected by this trend, because their electricity consumption does not fit in with the general electricity requirement and can therefore hardly be compensated for by other electricity consumers. This includes, in particular, aluminum production, but other branches of industry, particularly those in the chemical industry, are also heavily affected by this development.

Eine verstärkte Nutzung von volatilen Energiequellen hat nicht nur zur Folge, dass der Preis für die Bereitstellung elektrischer Energie insgesamt steigt, sondern auch dass die Verfügbarkeit von ausreichend großen elektrischen Energiemengen im Stromnetz nicht immer sichergestellt sein kann. Aus diesem Grund besteht das Problem, dass Industrieanlagen insbesondere aus dem energieintensiven Bereich in Gegenden mit diskontinuierlicher Stromversorgung voraussichtlich nicht mehr wirtschaftlich arbeiten können.Increased use of volatile energy sources not only means that the price for the provision of electrical energy increases overall, but also that the availability of sufficiently large amounts of electrical energy in the power grid cannot always be guaranteed. For this reason, there is the problem that industrial plants, in particular from the energy-intensive area in areas with discontinuous power supply, are unlikely to be able to work economically.

Bisher wird eine Schmelzflusselektrolysezelle über die der Zelle zugeführte Stromstärke gesteuert, wobei feste Annahmen zum thermodynamischen Gleichgewicht der Schmelzflusselektrolysezelle getroffen werden. Dies ist bei gleichbleibenden Randbedingungen, insbesondere Stromaufnahme, elektrischer Zellenwiderstand, thermische Auslegung der Schmelzflusselektrolysezelle oder gleichbleibende Abgasabfuhr, zuverlässig möglich.Up to now, a fused flux electrolysis cell has been controlled via the current strength supplied to the cell, fixed assumptions being made about the thermodynamic equilibrium of the fused flux electrolysis cell. This is reliably possible with constant boundary conditions, in particular current consumption, electrical cell resistance, thermal design of the fused-salt electrolysis cell or constant exhaust gas discharge.

Bekannte Schmelzflusselektrolyseverfahren sind also im regelungstechnischen Sinne Steuerungsverfahren, die sich auf konstante, sehr gut vorbestimmbare Randbedingungen verlassen können. In relativ großen Abständen, beispielsweise einmal täglich, wird die Temperatur der Schmelze im Innern der Schmelzflusselektrolysezelle bestimmt. Ferner wird ebenfalls in relativ großen Abständen, beispielsweise im Anschluss an die Bestimmung der Temperatur der Schmelze, die Erstarrungstemperatur bestimmt. Ein anderer Ansatz basiert auf der Bestimmung des AlF3-Gehalts der Schmelze. Auf der Basis dieser Werte wird durch eine gegebenenfalls erforderliche Anpassung der über die Schmelzflusselektrolysezelle abfallenden Spannung die Dicke der Kruste in einem praktikablen Bereich gehalten. Beispielsweise wird bei einer Schmelzflusselektrolysezelle angenommen, dass die Kruste eine geeignete Dicke hat, wenn die Temperatur der Schmelze 8°C über deren Erstarrungstemperatur liegt.Known fused flux electrolysis processes are therefore control processes in the control engineering sense, which can rely on constant, very easily predeterminable boundary conditions. The temperature of the melt inside the melt flow electrolysis cell is determined at relatively long intervals, for example once a day. Furthermore, the solidification temperature is also determined at relatively long intervals, for example after the temperature of the melt has been determined. Another approach is based on the determination of the AlF 3 content of the melt. On the basis of these values, the thickness of the crust is kept within a practicable range by adapting the voltage drop across the fused salt electrolysis cell, if necessary. For example, in the case of a fused metal electrolysis cell, it is assumed that the crust has a suitable thickness if the temperature of the melt is 8 ° C. above its solidification temperature.

Aus DE 26 15 652 A1 geht ein Verfahren zum Messen und Steuern der Energiebilanz von Aluminium-Öfen hervor, bei dem die Eintauchtiefe der Anode der Elektrolysezelle in Abhängigkeit einer im seitlichen Ofenfutter gemessenen Temperatur verändert wird.Out DE 26 15 652 A1 describes a method for measuring and controlling the energy balance of aluminum furnaces, in which the immersion depth of the anode of the electrolytic cell is changed as a function of a temperature measured in the furnace lining on the side.

GB 2 076 428 A offenbart ein Verfahren zum Betreiben einer Aluminiumelektrolysezelle, bei dem in Abhängigkeit einer gemessenen Zellwandtemperatur ein Wärmeaustrag durch Wärmerohre gesteuert wird. GB 2 076 428 A discloses a method for operating an aluminum electrolysis cell in which a heat dissipation through heat pipes is controlled as a function of a measured cell wall temperature.

CH 648 871 A5 beschreibt ein Verfahren zur Kontrolle des Bordes in einer Schmelzflusselektrolysezelle, bei dem die Eintauchtiefe der Anode in Abhängigkeit der zugeführten Energie unter Berücksichtigung der Stromstärke und des ohmschen Badwiderstands verändert wird. CH 648 871 A5 describes a method for checking the board in a fused-salt electrolysis cell, in which the immersion depth of the anode is changed depending on the energy supplied, taking into account the current strength and the ohmic bath resistance.

Aus der deutschen Patentanmeldung DE 10 2011 078656 A1 der Anmelderin geht ein Verfahren zum Betreiben einer Schmelzflusselektrolyseanlage hervor, bei dem die Schmelzflusselektrolyseanlage so gesteuert wird, dass die von ihr aufgenommene Menge an elektrischer Leistung an die gleichzeitig durch eine volatile Energiequelle eingespeiste Menge an elektrischer Leistung angepasst ist. Gemäß dem dort beschriebenen Verfahren lässt sich die Schmelzflusselektrolyseanlage als "virtuelle Batterie" im Stromnetz verwenden. Der Stromverbrauch der Schmelzflusselektrolyseanlage wird, innerhalb der Systemgrenzen der Anlage, an die im Stromnetz vorhandene Energiemenge durch eine entsprechende Steuerung der Stromaufnahme angepasst. Bei einer erhöhten Stromaufnahme wird überschüssige Energie durch Wärmetauscher an der Zellenwand der Schmelzflusselektrolysezelle abgeführt, um ein vollständiges Abschmelzen der Kruste im Inneren der Schmelzflusselektrolysezelle zu verhindern. Bei reduzierter Stromaufnahme wird durch die Wärmetauscher der Temperaturgradient an der Seitenwand der Schmelzflusselektrolysezelle reduziert, um ein zu großes Anwachsen dieser Kruste zu verhindern.From the German patent application DE 10 2011 078656 A1 The applicant reveals a method for operating a melt flow electrolysis system in which the melt flow electrolysis system is controlled in such a way that the amount of electrical power it consumes is adapted to the amount of electrical power simultaneously fed in by a volatile energy source. According to the method described there, the melt flow electrolysis system can be used as a "virtual battery" in the Use power grid. The power consumption of the melt flow electrolysis system is adjusted, within the system limits of the system, to the amount of energy available in the power grid by means of a corresponding control of the power consumption. In the event of increased power consumption, excess energy is dissipated by heat exchangers on the cell wall of the fused salt electrolysis cell in order to prevent complete melting of the crust inside the fused flux electrolysis cell. With reduced power consumption, the heat exchanger reduces the temperature gradient on the side wall of the fused metal electrolysis cell in order to prevent this crust from growing too large.

Angesichts der aus DE 10 2011 078656 A1 bekannten Erfindung besteht jedoch noch Verbesserungsbedarf beim Betrieb der Schmelzflusselektrolyseanlage, weil die Steuerung des Betriebs der Schmelzflusselektrolysezellen durch variable Stromaufnahme und gegebenenfalls damit gekoppelte zusätzliche Wärmeabfuhr oder Wärmezufuhr ungenau ist und daher noch keinen gesicherten Produktionsablauf bei variabler Stromstärke zulässt.Given the off DE 10 2011 078656 A1 known invention, however, there is still a need for improvement in the operation of the melt-flow electrolysis system, because the operation of the melt-flow electrolysis cells is controlled by variable Current consumption and any additional heat dissipation or supply coupled with it is imprecise and therefore does not yet allow a secure production process with a variable current intensity.

Um diesem Problem zu begegnen, stellt sich die vorliegende Erfindung die Aufgabe, ein Verfahren zum Betreiben einer Zelle einer Schmelzflusselektrolyseanlage, insbesondere zur Herstellung von Aluminium, sowie eine Schmelzflusselektrolyseanlage, insbesondere zur Herstellung von Aluminium, mit einer entsprechenden Schmelzflusselektrolysezelle bereitzustellen, wodurch ein wirtschaftlicher und prozesssicherer Produktionsablauf beim Betrieb der Schmelzflusselektrolyseanlage auch unter der Voraussetzung schwankender Verfügbarkeit von elektrischer Energie im Stromnetz möglich ist.In order to counter this problem, the present invention has the object of providing a method for operating a cell of a melt-flow electrolysis system, in particular for the production of aluminum, as well as a melt-flow electrolysis system, in particular for the production of aluminum, with a corresponding melt-flow electrolysis cell, whereby an economical and process-reliable Production process when operating the melt flow electrolysis system is also possible under the prerequisite of fluctuating availability of electrical energy in the power grid.

Eine Aufgabe der vorliegenden Erfindung besteht darin, ein Regelungsverfahren und eine Schmelzflusselektrolyseanlage des oben beschriebenen technischen Gebiets bereitzustellen, wodurch die Schmelzflusselektrolyse bei variabler Verfügbarkeit elektrischer Energie sicher betrieben werden kann, insbesondere ohne die Schmelzflusselektrolysezellen zusätzlich zu belasten oder die Effizienz der Schmelzflusselektrolyse, insbesondere der Herstellung von Aluminium, herabzusetzen.An object of the present invention is to provide a control method and a melt-flow electrolysis system of the technical field described above, whereby the melt-flow electrolysis can be operated safely with variable availability of electrical energy, in particular without additional loading of the melt-flow electrolysis cells or the efficiency of the melt-flow electrolysis, in particular the production of Aluminum.

DARSTELLUNG DER ERFINDUNGDISCLOSURE OF THE INVENTION

Ein erfindungsgemäßes Regelungsverfahren ist in Anspruch 1 definiert. Eine erfindungsgemäße Schmelzflusselektrolyseanlage ergibt sich aus Anspruch 8. Eine erfindungsgemäße Verwendung des Regelungsverfahrens oder der Schmelzflusselektrolyseanlage ergibt sich aus Anspruch 14. Vorteilhafte Weiterbildungen der Erfindung ergeben sich aus den Unteransprüchen.A control method according to the invention is defined in claim 1. A melt flow electrolysis system according to the invention results from claim 8. A use according to the invention of the control method or the melt flow electrolysis system results from claim 14. Advantageous further developments of the invention result from the subclaims.

Das erfindungsgemäße Regelungsverfahren zum Betreiben einer Zelle einer Schmelzflusselektrolyseanlage, insbesondere zur Herstellung von Aluminium, ist dadurch gekennzeichnet, dass eine erste Regelgröße eine Energiebilanz der Zelle ist, welche die in die Schmelzflusselektrolysezelle eintretende elektrische Energie und die aus der Schmelzflusselektrolysezelle austretende Wärmeenergie berücksichtigt, wobei eine zweite Regelgröße ein thermischer Zustand der Zelle ist.The control method according to the invention for operating a cell of a melt flow electrolysis system, in particular for the production of aluminum, is characterized in that a first control variable is an energy balance of the cell, which takes into account the electrical energy entering the melt flow electrolysis cell and the thermal energy exiting the melt flow electrolysis cell, with a second The controlled variable is a thermal state of the cell.

Im vorliegenden Zusammenhang wird unter einer "Regelung" beziehungsweise unter dem "Regeln" ein Vorgang verstanden, bei dem fortlaufend eine Größe, die "Regelgröße", erfasst, mit einer anderen Größe, der "Führungsgröße", verglichen und im Sinne einer Angleichung an die Führungsgröße beeinflusst wird. Für das Regeln ist der geschlossene Wirkungsablauf, bei dem die Regelgröße im Wirkungsweg des Regelkreises fortlaufend sich selbst beeinflusst, kennzeichnend. Im vorliegenden Zusammenhang wird unter einer "Regelung" beziehungsweise unter dem "Regeln" ferner ein Vorgang verstanden, bei dem fortlaufend die "Regelgröße" simuliert statt gemessen, mit der "Führungsgröße" verglichen und im Sinne einer Angleichung an die Führungsgröße beeinflusst wird. Auch bei dieser Form des Regelns im vorliegenden Sinne ist der geschlossene Wirkungsablauf, bei dem die Regelgröße im Wirkungsweg des Regelkreises fortlaufend sich selbst beeinflusst, kennzeichnend. Allerdings kann nach Erstellung eines Simulationsprogramms beispielsweise für den Wärmeaustrag aus einer Schmelzflusselektrolysezelle auf eine unmittelbare oder mittelbare Messung des Wärmeaustrags verzichtet und dieser stattdessen auf der Grundlage einer Simulation des Wärmeaustrags bestimmt werden.In the present context, “regulation” or “regulation” is understood to mean a process in which a variable, the “controlled variable”, is continuously recorded, compared with another variable, the “reference variable”, and in the sense of an approximation to the Reference variable is influenced. The closed action sequence, in which the controlled variable continuously influences itself in the action path of the control loop, is characteristic of the control. In the present context, “regulation” or “regulation” is also understood to mean a process in which the “controlled variable” is continuously simulated instead of measured, compared with the “reference variable” and influenced in the sense of an adjustment to the reference variable. With this form of control in the present sense, too, the closed action sequence, in which the controlled variable continuously influences itself in the action path of the control loop, is characteristic. However, once a simulation program has been created, for example for the heat output from a fused-salt electrolysis cell, direct or indirect measurement of the heat output can be dispensed with and this can instead be determined on the basis of a simulation of the heat output.

Bisher war der ausschließliche Garant für ein stabiles Schmelzflusselektrolyseverfahren im vorliegenden Zusammenhang eine gleichbleibende Elektrolyttemperatur in der Zelle.Until now, the only guarantee for a stable fused-salt electrolysis process in the present context was a constant electrolyte temperature in the cell.

Bei variierenden Energieverfügbarkeiten im Stromnetz, muss von der bisherigen Betriebsweise abgewichen werden. Statt einer Steuerung des Betriebs der Schmelzflusselektrolysezelle mit dem Ziel einer gleichbleibenden Elektrolyttemperatur und Krustendicke wird erfindungsgemäß der Betrieb der Schmelzflusselektrolysezelle geregelt, und zwar so, dass die Elektrolyttemperatur sich in einem relativ breiten Temperaturband befindet. Dies wird erfindungsgemäß durch die regelungstechnische Berücksichtigung der Wärmebilanz bewirkt. Unter der Wärmebilanz wird im vorliegenden Zusammenhang eine Energiebilanz verstanden, welche die in die Schmelzflusselektrolysezelle eintretende elektrische Energie und die aus der Schmelzflusselektrolysezelle austretende Wärmeenergie berücksichtigt.If the availability of energy in the power grid varies, the previous mode of operation must be deviated from. Instead of controlling the operation of the fused metal electrolysis cell with the aim of a constant electrolyte temperature and crust thickness, the operation of the Melt-flow electrolysis cell regulated in such a way that the electrolyte temperature is in a relatively wide temperature range. According to the invention, this is brought about by the control-related consideration of the heat balance. In the present context, the heat balance is understood to mean an energy balance which takes into account the electrical energy entering the fused electrolysis cell and the thermal energy exiting the fused electrolysis cell.

Bevorzugt wird im Fall einer Aluminiumelektrolyseanlage bzw. Aluminiumelektrolysezelle ferner der für die Produktion von Aluminium verwendete Anteil der in die Aluminiumelektrolysezelle eintretenden elektrischen Energie bestimmt. Alternativ kann dieser Anteil der in die Aluminiumelektrolysezelle eintretenden elektrischen Energie als konstant angenommen und der als Wärme in die Aluminiumelektrolysezelle eingebrachte Anteil aus der Differenz zwischen der gesamten elektrischen Energie und der als konstant angenommenen für die Produktion verwendeten Energie bestimmt werden.In the case of an aluminum electrolysis system or aluminum electrolysis cell, the proportion of the electrical energy entering the aluminum electrolysis cell used for the production of aluminum is also preferably determined. Alternatively, this proportion of the electrical energy entering the aluminum electrolysis cell can be assumed to be constant and the proportion introduced as heat into the aluminum electrolysis cell can be determined from the difference between the total electrical energy and the energy used for production, which is assumed to be constant.

Erfindungsgemäß wird folglich die Wärmebilanz der Schmelzflusselektrolysezelle ermittelt und der Betrieb der Schmelzflusselektrolysezelle auf der Grundlage der Wärmebilanz als Regelgröße geregelt. Bevorzugt wird beziehungsweise werden ein Thermoelement und/oder eine Vorrichtung, insbesondere eine Messvorrichtung, zur Bestimmung eines Volumenstroms einer Abluft von der Zelle und/oder eine Vorrichtung, insbesondere eine Messvorrichtung, zur Bestimmung eines Volumenstroms eines Wärmetransportfluids in einem Wärmetauscher an der Zelle als ein Messglied oder mehrere Messglieder zur Bestimmung der ersten Regelgröße, d.h. der Wärmebilanz, verwendet.According to the invention, the heat balance of the fused flux electrolysis cell is consequently determined and the operation of the fused flow electrolysis cell is regulated on the basis of the heat balance as a control variable. A thermocouple and / or a device, in particular a measuring device, for determining a volume flow of exhaust air from the cell and / or a device, in particular a measuring device, for determining a volume flow of a heat transport fluid in a heat exchanger on the cell is or are preferred as a measuring element or several measuring elements are used to determine the first controlled variable, ie the heat balance.

Bevorzugt werden mindestens 6, bevorzugt mindestens 12, weiter bevorzugt mindestens 30, weiter bevorzugt mindestens 60, Thermoelemente an der Zelle angeordnet, um die Temperaturverteilung an der Zelle und damit auch die Wärmebilanz möglichst genau bestimmen zu können.At least 6, preferably at least 12, more preferably at least 30, more preferably at least are preferred 60, thermocouples arranged on the cell in order to be able to determine the temperature distribution on the cell and thus also the heat balance as precisely as possible.

Gemäß einer Ausführungsform werden nicht alle Schmelzflusselektrolysezellen einer Schmelzflusselektrolyseanlage, insbesondere nur eine Schmelzflusselektrolysezelle einer Schmelzflusselektrolyseanlage mit mehr als einer Schmelzflusselektrolysezelle mit dem Thermoelement oder den mehreren Thermoelementen versehen. Dies vereinfacht den konstruktiven Aufwand der Gesamtanlage und erreicht weitgehend das gewünschte Ziel des geregelten Betreibens der Schmelzflusselektrolyseanlage.According to one embodiment, not all of the melt flow electrolysis cells of a melt flow electrolysis system, in particular only one melt flow electrolysis cell of a melt flow electrolysis system with more than one melt flow electrolysis cell, are provided with the thermocouple or the multiple thermocouples. This simplifies the design effort of the overall system and largely achieves the desired goal of the regulated operation of the melt flow electrolysis system.

Die Thermoelemente können einzeln oder gemeinsam als Messglied im regelungstechnischen Sinne fungieren. Dies gilt grundsätzlich auch für die Vorrichtung zur Bestimmung des Volumenstroms der Abluft von der Zelle, die alternativ oder zusätzlich zum Volumenstrom den Massenstrom bestimmen kann und bevorzugt auch Informationen zur Temperatur der Abluft bestimmen kann.The thermocouples can function individually or jointly as a measuring element in the control engineering sense. This basically also applies to the device for determining the volume flow of the exhaust air from the cell, which can determine the mass flow as an alternative or in addition to the volume flow and can preferably also determine information on the temperature of the exhaust air.

Eine solche Vorrichtung zur Bestimmung des Volumenstroms der Abluft von der Zelle oder die Vorrichtung zur Bestimmung eines Volumenstroms des Wärmetransportfluids in dem Wärmetauscher kann beispielsweise auch über die Bestimmung einer Drehzahl eines Ventilators oder eines entsprechenden Elements funktionieren, dies auch indirekt, beispielsweise über die Energieaufnahme oder das (Dreh-)Feld eines den Ventilator antreibenden Elektromotors. Auf diese Weise ist es möglich, den Volumenstrom von Abluft bzw. Wärmetransportfluid zu bestimmen, ohne ihn unmittelbar zu messen, weil der Volumenstrom durch den Ventilator oder ein entsprechendes Element zumindest zu einem wesentlichen Anteil erzeugt wird. Gleichwohl kann diese Bestimmung des Volumenstroms bei der Regelung des Betriebs der Schmelzflusselektrolysezelle als "Messung" verarbeitet werden.Such a device for determining the volume flow of the exhaust air from the cell or the device for determining a volume flow of the heat transfer fluid in the heat exchanger can also function, for example, by determining a speed of a fan or a corresponding element, also indirectly, for example via the energy consumption or the (Rotary) field of an electric motor driving the fan. In this way it is possible to determine the volume flow of exhaust air or heat transport fluid without measuring it directly, because the volume flow is generated at least to a substantial extent by the fan or a corresponding element. Nevertheless, this determination of the volume flow in the Regulation of the operation of the fused metal electrolysis cell can be processed as "measurement".

Das genannte Wärmetransportfluid kann insbesondere Luft sein, die beispielsweise in einem grundsätzlich bekannten Wärmetauscher an der Zellenwand entlang geführt werden kann. Auch hinsichtlich des Wärmetransportfluids kann neben dem Volumenstrom oder anstelle des Volumenstroms ein Massenstrom bestimmt werden, und auch die Temperatur des Wärmetransportfluids kann bevorzugt bestimmt werden. Der Wärmetauscher kann bei Verwendung entsprechend temperierter Wärmetransportfluide auf das Ausmaß der Kühlung bzw. des Wärmeverlusts der Schmelzflusselektrolysezelle und somit insbesondere die Dicke der Kruste entlang ihres Randes Einfluss nehmen und somit in mehrfacher Hinsicht die Wärmebilanz beeinflussen.Said heat transfer fluid can in particular be air, which can be guided along the cell wall, for example, in a basically known heat exchanger. With regard to the heat transport fluid, in addition to the volume flow or instead of the volume flow, a mass flow can also be determined, and the temperature of the heat transport fluid can also preferably be determined. When using appropriately tempered heat transfer fluids, the heat exchanger can influence the extent of cooling or heat loss of the fused-salt electrolysis cell and thus in particular the thickness of the crust along its edge and thus influence the heat balance in several ways.

Bevorzugt ist das Regelungsverfahren, insbesondere die obengenannten Einrichtungen Thermoelement, Messvorrichtung zur Bestimmung eines Volumenstroms einer Abluft von der Zelle und Messvorrichtung zur Bestimmung eines Volumenstroms eines Wärmetransportfluids in einem Wärmetauscher an der Zelle, zur kontinuierlichen Erfassung einer der Zelle zugeführten Wärme und einer von der Zelle abgeführte Wärme geeignet und ausgestaltet. Somit ist es besonders leicht möglich, die Wärmebilanz als Regelgröße zu nutzen. Neben den obigen möglichen Messgliedern bestehen jedoch auch Alternativen wie Wärmekameras, um bei der Bestimmung der Wärmebilanz zu unterstützen.The control method is preferred, in particular the above-mentioned thermocouple devices, measuring device for determining a volume flow of an exhaust air from the cell and measuring device for determining a volume flow of a heat transfer fluid in a heat exchanger on the cell, for continuous detection of a heat supplied to the cell and a heat dissipated from the cell Heat suitable and designed. This makes it particularly easy to use the heat balance as a control variable. In addition to the above possible measuring elements, however, there are also alternatives such as thermal cameras to support the determination of the thermal balance.

In einer bevorzugten Ausführungsform weist die Zelle Seitenwände, einen Boden und eine Abluftführung auf, wobei an oder in zumindest einer der Seitenwände, dem Boden oder der Abluftführung, bevorzugt an oder in allen Seitenwänden und dem Boden und besonders bevorzugt auch an oder in der Abluftführung angeordnete Thermoelemente als Messglieder zur Bestimmung der Wärmebilanz verwendet werden. Alternativ ist es auch möglich, nur einige der Seitenwände, nur den Boden, nur die Abluftführung oder Mischungen hiervon für die Anordnung von Thermoelementen als Messglieder zu verwenden.In a preferred embodiment, the cell has side walls, a floor and an exhaust air duct, with arranged on or in at least one of the side walls, the floor or the exhaust air duct, preferably on or in all side walls and the floor and particularly preferably also on or in the exhaust air duct Thermocouples are used as measuring elements to determine the heat balance. Alternatively is It is also possible to use only some of the side walls, only the floor, only the exhaust air duct or mixtures thereof for the arrangement of thermocouples as measuring elements.

Bevorzugt wird mindestens ein Wärmetauscher und/oder mindestens eine Abgasstromklappe und/oder eine chemische Zusammensetzung der Schmelze, insbesondere eine AlF3 Dosierung, und/oder mindestens eine Traverse zur Positionierung mindestens einer Anode in der Zelle als Stellglied zur Einwirkung auf einen Wärmeeintrag und/oder einen Wärmeaustrag verwendet. Durch die obengenannten Elemente ist es möglich, den Wärmeeintrag und/oder Wärmeaustrag in relativ weiten Grenzen zu variieren, wobei der Wärmeeintrag beziehungsweise Wärmeaustrag als Stellgröße bei der Regelung der Wärmebilanz genutzt werden. Grundsätzlich gibt es auch andere Möglichkeiten, den Wärmeeintrag beziehungsweise Wärmeaustrag zu variieren, aber die oben genannten Elemente haben sich als besonders wirkungsvoll im Zusammenhang mit Schmelzflusselektrolysezellen herausgestellt.At least one heat exchanger and / or at least one exhaust gas flow flap and / or a chemical composition of the melt, in particular an AlF 3 metering, and / or at least one crossbeam for positioning at least one anode in the cell as an actuator to act on a heat input and / or are preferred a heat discharge is used. The above-mentioned elements make it possible to vary the heat input and / or heat output within relatively wide limits, the heat input or heat output being used as a manipulated variable when regulating the heat balance. In principle, there are also other ways of varying the heat input or heat output, but the above-mentioned elements have proven to be particularly effective in connection with fused-salt electrolysis cells.

Bevorzugt wird bei einer Veränderung der von der Schmelzflusselektrolyseanlage oder -zelle aufgenommenen Stromstärke, die maßgeblich den Energie- und damit auch den Wärmeeintrag definiert, eine entsprechende Anpassung der über die Schmelzflusselektrolysezelle abfallenden Spannung vorgenommen. Dies kann insbesondere durch eine Veränderung des Abstands zwischen der Anode oder mehreren Anoden und der Kathode oder mehreren Kathoden bewirkt werden. Ein Ansteigen des Stroms bringt dabei grundsätzlich mehr Wärme in die Schmelzflusselektrolysezelle, während ein Reduzieren der Spannung, d.h. ein Reduzieren des Abstands zwischen den Elektroden, zu einem grundsätzlich geringeren Wärmeeintrag führt. Bevorzugt wird ferner durch Stellung der Abgasstromklappe oder Wärmetauscher weiter auf den Wärmeaustrag aus der Schmelzflusselektrolysezelle Einfluss genommen, weil die Variation des Wärmeeintrags effektiver möglich ist als diejenige des Wärmeaustrags.In the event of a change in the current intensity absorbed by the fused-salt electrolysis system or cell, which significantly defines the energy and thus also the heat input, a corresponding adjustment of the voltage drop across the fused-melt electrolysis cell is carried out. This can be brought about in particular by changing the distance between the anode or a plurality of anodes and the cathode or a plurality of cathodes. An increase in the current basically brings more heat into the fused-salt electrolysis cell, while a reduction in the voltage, ie a reduction in the distance between the electrodes, leads to a fundamentally lower heat input. In addition, the position of the exhaust gas flow flap or heat exchanger is preferably used to further influence the heat output from the fused salt electrolysis cell taken because the variation of the heat input is possible more effectively than that of the heat output.

Mit Vorteil werden auch ein Eintrag von zu schmelzendem Material, insbesondere Aluminiumoxid und Kryolith, und/oder ein Austrag von geschmolzenem Material, insbesondere Aluminium, und/oder eine Änderung einer Schmelzflusselektrolysestromstärke als Störgröße berücksichtigt. Der Eintrag von zu schmelzendem Material verändert nicht nur die Temperatur des Elektrolytbades, sondern auch dessen chemische Zusammensetzung, was Einfluss auf die Wärmebilanz des Betriebs der Schmelzflusselektrolysezelle hat. Ähnliches gilt auch für den Austrag, das heißt die Entnahme von geschmolzenem Material, das vor allem Wärmeenergie aus dem System entnimmt und zum Teil auch dessen chemische Zusammensetzung verändert. Die Schmelzflusselektrolysestromstärke ändert den Energieeintrag und damit die zugeführte Wärmemenge. Die Stromstärke kann insbesondere aufgrund variabler im Stromnetz vorhandener Energie und damit vorbei an der Regelung der Schmelzflusselektrolyse selbst, in gewissen Grenzen unkontrolliert, variieren. Durch die Berücksichtigung der Wärmebilanz können derartige Änderungen der Schmelzflusselektrolysestromstärke im Hinblick auf den von ihnen erzielten Effekt berücksichtigt werden, sodass sichergestellt sein kann, dass alle Konsequenzen der variierenden Stromstärken im Hinblick auf die Prozesssicherheit berücksichtigt werden können.An entry of material to be melted, in particular aluminum oxide and cryolite, and / or a discharge of molten material, in particular aluminum, and / or a change in a melt flow electrolysis current strength are also taken into account as a disturbance variable. The entry of material to be melted changes not only the temperature of the electrolyte bath, but also its chemical composition, which has an impact on the heat balance of the operation of the melt flow electrolysis cell. The same applies to the discharge, i.e. the removal of molten material, which primarily takes thermal energy from the system and also changes its chemical composition in part. The melt flow electrolysis current strength changes the energy input and thus the amount of heat supplied. The strength of the current can vary in an uncontrolled manner within certain limits, in particular due to the variable energy present in the power network and thus bypassing the regulation of the fused-salt electrolysis itself. By taking the heat balance into account, such changes in the melt flow electrolysis current intensity can be taken into account with regard to the effect achieved by them, so that it can be ensured that all the consequences of the varying current intensities with regard to process reliability can be taken into account.

In einer bevorzugten Ausführungsform des Regelungsverfahrens ist eine dritte Regelgröße ein chemischer Zustand der Zelle. Unter dem thermischen Zustand der Zelle ist im vorliegenden Zusammenhang insbesondere die Temperatur des Elektrolyten als maßgebliche Größe zu verstehen. Natürlich tragen auch andere Elemente der Zelle zu deren thermischem Zustand bei. Der kritischste Teil der Zelle ist jedoch der Elektrolyt, weil dessen Temperatur auf jeden Fall oberhalb seiner Erstarrungstemperatur gehalten werden muss, um die Schmelzflusselektrolyseanlage funktionsfähig zu halten. Der chemische Zustand der Zelle ist deswegen auch maßgeblich durch die Erstarrungstemperatur des Elektrolyten bestimmt, die insbesondere vom "AlF3-Überschuss" abhängt.In a preferred embodiment of the control method, a third control variable is a chemical state of the cell. In the present context, the thermal state of the cell is to be understood in particular as the temperature of the electrolyte as a decisive variable. Of course, other elements of the cell also contribute to its thermal Condition at. The most critical part of the cell, however, is the electrolyte, because its temperature must be kept above its solidification temperature in any case in order to keep the melt flow electrolysis system functional. The chemical state of the cell is therefore also largely determined by the solidification temperature of the electrolyte, which depends in particular on the "AlF 3 excess".

Eine erfindungsgemäße Schmelzflusselektrolyseanlage, insbesondere zur Herstellung von Aluminium, mit einer Schmelzflusselektrolysezelle ist dadurch gekennzeichnet, dass die Schmelzflusselektrolyseanlage eine Regelungsvorrichtung aufweist, die zur Ausführung eines der oben beschriebenen Regelungsverfahren ausgebildet ist.A melt-flow electrolysis system according to the invention, in particular for the production of aluminum, with a melt-flow electrolysis cell is characterized in that the melt-flow electrolysis system has a control device which is designed to carry out one of the control methods described above.

Bevorzugt umfasst die Schmelzflusselektrolyseanlage ein Thermoelement und/oder eine Messvorrichtung zur Bestimmung eines Volumenstroms einer Abluft von der Schmelzflusselektrolysezelle und/oder, sofern bevorzugt ein Wärmetauscher zur Beeinflussung eines Wärmeeintrags oder Wärmeaustrags mittels eines Wärmetransportfluids an zumindest einer Außenfläche der Schmelzflusselektrolysezelle umfasst ist, eine Messvorrichtung zur Bestimmung eines Volumenstroms des Wärmetransportfluids in dem Wärmetauscher an der Schmelzflusselektrolysezelle. Wie oben beschrieben wurde, eignen sich diese Elemente besonders gut dazu, als Messglied bei der erfindungsgemäßen Regelung genutzt zu werden, weil sie aussagekräftige Informationen zur Bestimmung der Wärmebilanz der Schmelzflusselektrolysezelle bereitstellen und die Regelung daher besonders leicht umsetzten lassen.Preferably, the melt flow electrolysis system comprises a thermocouple and / or a measuring device for determining a volume flow of exhaust air from the melt flow electrolysis cell and / or, if a heat exchanger for influencing a heat input or heat output by means of a heat transport fluid on at least one outer surface of the melt flow electrolysis cell is included, a measuring device for determination a volume flow rate of the heat transport fluid in the heat exchanger at the fused salt electrolysis cell. As described above, these elements are particularly well suited to be used as measuring elements in the inventive control, because they provide meaningful information for determining the heat balance of the fused metal electrolysis cell and therefore allow the control to be implemented particularly easily.

Die Schmelzflusselektrolysezelle einer bevorzugten Schmelzflusselektrolyseanlage weist Seitenwände, einen Boden und eine Abluftführung auf, wobei an oder in zumindest einer der Seitenwände, dem Boden oder der Abluftführung, bevorzugt an oder in allen Seitenwänden und dem Boden und besonders bevorzugt auch an oder in der Abluftführung Thermoelemente angeordnet sind. Dies ermöglicht es besonders gut, die Wärmebilanz der Schmelzflusselektrolysezelle zu bestimmen und eignet sich daher besonders gut zum Einsatz im erfindungsgemäßen Zusammenhang.The melt flow electrolysis cell of a preferred melt flow electrolysis system has side walls, a base and an exhaust air duct, with thermocouples on or in at least one of the side walls, the base or the exhaust air duct, preferably on or in all side walls and the base and particularly preferably also on or in the exhaust air duct are arranged. This makes it possible to determine the heat balance of the fusible flow electrolysis cell particularly well and is therefore particularly suitable for use in the context of the invention.

Mit Vorteil umfasst die Schmelzflusselektrolyseanlage einen Wärmetauscher zur Beeinflussung eines Wärmeeintrags oder Wärmeaustrags mittels eines Wärmetransportfluids an zumindest einer Außenfläche der Schmelzflusselektrolysezelle und/oder eine einstellbare Abgasstromklappe zur Beeinflussung eines Volumenstroms eines Abgases von der Schmelzflusselektrolysezelle und/oder eine Vorrichtung zur Veränderung einer chemischen Zusammensetzung der Schmelze, insbesondere zur Veränderung einer Dosierung von AlF3 in der Schmelze, und/oder eine Traverse zur Positionierung einer Anode in der Schmelzflusselektrolysezelle. Durch die genannten Elemente, die sich als Stellglieder im regelungstechnischen Sinne einsetzen lassen, können Wärmeverlust und Wärmeeintrag in weiten Grenzen auf effiziente Art und Weise eingestellt und variiert werden, um die Wärmebilanz bestmöglich und effizient an ihren Sollwert anzupassen. Grundsätzlich gibt es auch andere Möglichkeiten, auf die Wärmebilanz Einfluss zu nehmen, die jedoch weniger effektiv und daher ineffizient funktionieren.Advantageously, the melt flow electrolysis system comprises a heat exchanger for influencing a heat input or heat output by means of a heat transport fluid on at least one outer surface of the melt flow electrolysis cell and / or an adjustable exhaust gas flow flap for influencing a volume flow of an exhaust gas from the melt flow electrolysis cell and / or a device for changing a chemical composition of the melt, in particular for changing a dosage of AlF 3 in the melt, and / or a cross member for positioning an anode in the melt flow electrolysis cell. With the elements mentioned, which can be used as actuators in the control engineering sense, heat loss and heat input can be efficiently adjusted and varied within wide limits in order to adapt the heat balance as efficiently as possible to its setpoint. There are basically other ways of influencing the heat balance, but they are less effective and therefore inefficient.

Ferner umfasst eine bevorzugte Schmelzflusselektrolyseanlage eine Vorrichtung zur Bestimmung einer Masse von in die Schmelzflusselektrolysezelle eingebrachtem, zu schmelzendem Material, insbesondere Aluminiumoxid und Kryolith, und/oder eine Vorrichtung zur Bestimmung einer Masse von aus der Schmelzflusselektrolysezelle entnommenem, geschmolzenem Material, insbesondere Aluminium. Das in die Zelle eingebrachte und aus der Zelle entnommene Material verändert nicht nur die Wärmebilanz, indem Wärme aus dem System Schmelzflusselektrolysezelle entnommen oder in es hineingebracht wird, sondern ändert zum Teil auch die chemische Zusammensetzung des Inhaltes der Schmelzflusselektrolysezelle, was insbesondere Einfluss auf die Erstarrungstemperatur des Elektrolyten hat und bei der Regelung der Wärmebilanz daher berücksichtigt werden sollte. Hierzu ist anzumerken, dass auch die Änderung der Temperatur des in der Zelle befindlichen Materials wegen der hierdurch hervorgerufenen Änderung der Dicke der Randkruste auf die chemische Zusammensetzung der Schmelze Einfluss nimmt. Eine Erhöhung der Temperatur führt zu einem weiteren Abschmelzen der Kruste und damit einer Verringerung des Anteils an AlF3 in der Schmelze. Da dieser zuletzt genannte Prozess eine gewisse Trägheit und Pendelbewegung aufweist, war die Bestimmung der chemischen Zusammensetzung kurz nach einer Variierung der der Zelle zugeführten Stromstärke fehlerbehaftet. Durch die erfindungsgemäße Regelung können diese Fehler ausgeglichen und Fehlinterpretationen vermieden werden.Furthermore, a preferred melt-flow electrolysis system comprises a device for determining a mass of material to be melted introduced into the melt-flow electrolysis cell, in particular aluminum oxide and cryolite, and / or a device for determining a mass of molten material removed from the melt-flow electrolysis cell, in particular aluminum. The material introduced into the cell and removed from the cell not only changes the heat balance in that heat is removed from or brought into the fused metal electrolysis cell system, but also partially changes the chemical composition of the contents of the cell Fused metal electrolysis cell, which has an influence in particular on the solidification temperature of the electrolyte and should therefore be taken into account when regulating the heat balance. It should be noted here that the change in the temperature of the material in the cell also has an influence on the chemical composition of the melt due to the change in the thickness of the edge crust caused by this. An increase in temperature leads to further melting of the crust and thus a reduction in the proportion of AlF 3 in the melt. Since this last-mentioned process exhibits a certain inertia and pendulum motion, the determination of the chemical composition was error-prone shortly after the current intensity supplied to the cell was varied. The control according to the invention can compensate for these errors and avoid misinterpretations.

Erfindungsgemäß wird das oben beschriebene Regelungsverfahren oder eine oben beschriebene Schmelzflusselektrolyseanlage, sofern die Schmelzflusselektrolyseanlage an ein Stromnetz angeschlossen ist, um mit elektrischer Energie für die Schmelzflusselektrolyse versorgt zu werden, mit anderen Worten wobei ein für den Betrieb der Zelle genutzter Strom aus dem Stromnetz zugeführt wird, zum Ausgleichen von Schwankungen einer Einspeisung von Energie in das Stromnetz verwendet. Solche Schwankungen führen zu einem Ungleichgewicht zwischen Einspeisung und Verbrauch, was binnen kürzester Zeit Frequenzabweichungen und/oder Spannungsabweichungen im Netz zur Folge hat, die den stabilen Betrieb des Netzes gefährden und daher zur Vermeidung von Netzzusammenbrüchen ("Blackout") unverzüglich korrigiert werden müssen. Dadurch, dass die erfindungsgemäße Schmelzflusselektrolyseanlage beziehungsweise das Regelungsverfahren zum Betrieb der Schmelzflusselektrolyseanlage so ausgebildet sind, dass ein Betrieb der Schmelzflusselektrolyseanlage innerhalb der Systemgrenzen mit unterschiedlichen Abnahmeleistungen möglich ist, kann das Schmelzflusselektrolyseverfahren sehr gut als Puffer zum Ausgleich dieser Leistungsbilanz-Ungleichgewichte und damit zur Netzstabilisierung verwendet werden.According to the invention, the above-described control method or a melt-flow electrolysis system described above, provided that the melt-flow electrolysis system is connected to a power grid in order to be supplied with electrical energy for the melt-flow electrolysis, in other words wherein a current used for operating the cell is supplied from the power grid, used to compensate for fluctuations in feeding energy into the power grid. Such fluctuations lead to an imbalance between feed-in and consumption, which results in frequency deviations and / or voltage deviations in the network within a very short time, which endanger the stable operation of the network and must therefore be corrected immediately to avoid network breakdowns ("blackouts"). The fact that the melt flow electrolysis system according to the invention or the control method for operating the melt flow electrolysis system are designed in such a way that the melt flow electrolysis system can be operated within the system limits with different consumption capacities the fused-salt electrolysis process can be used very well as a buffer to compensate for these power balance imbalances and thus to stabilize the grid.

Dies ist von besonderem Vorteil, wenn die eingespeiste Energie von einer volatilen Stromquelle, insbesondere einer Windkraftanlage oder einer Solaranlage stammt. Denn durch die erfindungsgemäße Verwendung kann die Netzstabilität auch bei einem relative großen Anteil volatiler Stromquellen an der Einspeisung von Energie in das Stromnetz in vertretbaren Grenzen sichergestellt werden, ohne noch höhere Kosten für die Netzstabilität zu erzeugen. Dies ermöglicht es praktisch erst, einen großen Anteil von volatilen Stromquellen und damit das volle Potenzial regenerativer Energiequellen in Industrieländern zu nutzen.This is of particular advantage if the energy fed in comes from a volatile power source, in particular a wind power plant or a solar plant. This is because the use according to the invention enables network stability to be ensured within reasonable limits even with a relatively large proportion of volatile power sources in the feed-in of energy into the power network, without generating even higher costs for network stability. In practice, this makes it possible for the first time to use a large proportion of volatile power sources and thus the full potential of regenerative energy sources in industrialized countries.

Weitere Merkmale und Vorteile der Erfindung ergeben sich aus der nachfolgenden Figurenbeschreibung und der Gesamtheit der Patentansprüche.Further features and advantages of the invention emerge from the following description of the figures and the entirety of the patent claims.

KURZE FIGURENBESCHREIBUNGSHORT DESCRIPTION OF THE FIGURES

  • Figur 1 zeigt ein Diagramm einer Prozessführung mittels geschlossener Echtzeitwärmebilanzregelung. Figure 1 shows a diagram of process management using closed real-time heat balance control.
  • Figur 2 zeigt eine schematische Darstellung einer Schmelzflusselektrolysezelle. Figure 2 shows a schematic representation of a melt flow electrolysis cell.

Figur 1 zeigt ein Diagramm einer bevorzugten Prozessführung mittels geschlossener Echtzeitwärmebilanzregelung. Als Führungsgröße w(t) wird die Wärmebilanz angesetzt. Eine Regelabweichung e(t) der Wärmebilanz, das heißt eine Abweichung der Wärmebilanz vom Sollwert, wird durch einen Regler auf Grundlage einer Wärmebilanzrückführung ym(t) ausgeglichen. Der Regler ermittelt durch den Vergleich zwischen Führungsgröße w(t) und Rückführung ym(t) eine Abweichung der ermittelten Wärmebilanz y(t) von der Führungsgröße w(t) und ermittelt entsprechende Gegenmaßnahmen, um die Regelgröße an die Führungsgröße anzupassen. Figure 1 shows a diagram of a preferred process management by means of closed real-time heat balance control. The heat balance is used as the reference variable w (t). A control deviation e (t) of the heat balance, that is to say a deviation of the heat balance from the target value, is compensated for by a controller on the basis of a heat balance feedback y m (t). The controller determines through the comparison between the reference variable w (t) and feedback y m (t) a deviation of the determined heat balance y (t) from the reference variable w (t) and determines appropriate countermeasures in order to adapt the controlled variable to the reference variable.

Als allgemeine Stellgröße u(t) werden der Wärmeverlust beziehungsweise Wärmeeintrag angesehen. Um die allgemeine Stellgröße u(t) einzustellen, kann der Regler beispielsweise Einfluss auf einen Wärmetauscher, auf Abgasstromklappen, die Badchemie und die Spannung im Innern der Schmelzflusselektrolysezelle nehmen. Die konkrete Stellgröße uS(t), die vom Regler beeinflusst werden kann, kann beispielsweise die Klappenposition von in einer Abgasführung vorhandenen Abgasstromklappen, eine Dosierung von AlF3 im Elektrolytbad, einen Strömungsgeschwindigkeit von Wärmetransportfluid im Wärmetauscher oder eine Traversenposition, d.h. eine relative Position einer oder mehrerer Anoden in der Schmelzflusselektrolysezelle, sein, über welche der Abstand zwischen der Anode/den Anoden an der Traverse und dem als Katode fungierenden Aluminiumsee in einer Aluminiumelektrolysezelle oder allgemein einer Kathode eingestellt werden kann. Bei der Regelstrecke handelt es sich also um die Schmelzflusselektrolysezelle mit ihren Bestandteilen wie gegebenenfalls dem Wärmetauscher, der Abgasstromführung, der Traverse, Gebläse, Klappen etc.The heat loss or heat input are viewed as the general manipulated variable u (t). In order to set the general manipulated variable u (t), the controller can, for example, influence a heat exchanger, exhaust gas flow dampers, the bath chemistry and the voltage inside the molten electrolysis cell. The specific manipulated variable u S (t), which can be influenced by the controller, can, for example, be the flap position of exhaust gas flow flaps in an exhaust gas duct, a dosage of AlF 3 in the electrolyte bath, a flow rate of heat transfer fluid in the heat exchanger or a crossbar position, i.e. a relative position of a or several anodes in the fused-salt electrolysis cell, via which the distance between the anode / the anodes on the traverse and the aluminum pool functioning as a cathode in an aluminum electrolysis cell or generally a cathode can be adjusted. The controlled system is therefore the fused metal electrolysis cell with its components such as the heat exchanger, the exhaust gas flow guide, the crossbeam, fan, flaps, etc.

Hierdurch können also auch als Störgröße d(t) anzusehende äußere Einwirkungen, insbesondere eine Stromstärkeänderung aufgrund von Netzschwankungen, operationelle Eingriffe an der Schmelzflusselektrolysezelle oder eine variierende Produktionseffizienz bei der Herstellung von Aluminium, berücksichtigt werden. Da diese Störgrößen Einfluss auf die Wärmebilanz der Schmelzflusselektrolysezelle haben, können sie auf die erfindungsgemäße Weise weggeregelt werden.As a result, external influences, in particular a change in current strength due to network fluctuations, operational interventions in the fused-salt electrolysis cell or a varying production efficiency in the production of aluminum can also be taken into account as a disturbance variable d (t). Since these disturbance variables have an influence on the heat balance of the fused-salt electrolysis cell, they can be regulated away in the manner according to the invention.

Die Wärmebilanz kann beispielsweise durch Thermoelemente zur Messung der Temperaturen an den Seitenwänden, dem Boden und der Abluftführung sowie durch Elemente zur Bestimmung eines Volumenstroms sowohl der Abluft als auch eines möglicherweise durch einen Wärmetauscher fließenden Wärmetransportfluids im Zusammenhang mit einer Auswertungseinheit bestimmt werden. Die durch diese Messglieder gemessenen und ausgewerteten Daten werden dem Regler zugeführt, um die entsprechenden Stellglieder passend einzustellen.The heat balance can be determined, for example, by thermocouples for measuring the temperatures on the side walls, the floor and the exhaust air duct as well as by elements for determining a volume flow of both the exhaust air and a heat transfer fluid possibly flowing through a heat exchanger in connection with an evaluation unit. The data measured and evaluated by these measuring elements are fed to the controller in order to set the corresponding actuators appropriately.

Zusammengefasst lässt sich feststellen, dass die Wärme in der Schmelzflusselektrolysezelle hauptsächlich im Bereich des Anoden-Katodenabstandes erzeugt wird. Eine Verringerung des Abstands bei Stromstärkeerhöhung und eine Vergrößerung des Abstands bei Stromstärkeverringerung stellt eine erste Maßnahme zur Regelung der Wärmebilanz dar. Hierdurch wird der Ohm'sche Widerstand der Schmelzflusselektrolysezelle variiert, was in gewissen Grenzen, die insbesondere durch einen Mindestabstand zwischen Anode und Aluminiumsee sowie ein energieeffizientes Verfahren bestimmt sind, möglich ist. Zusätzlich ist es möglich, über optionale Wärmetauscher beispielsweise an den Seitenwänden der Schmelzflusselektrolysezelle Wärme von der Schmelzflusselektrolysezelle abzuführen und ihr zuzuführen, falls die vom Stromnetz zur Verfügung gestellte Energie ein Aufrechterhalten des Schmelzflusselektrolyseprozesses ansonsten nicht ermöglichen sollte. Weiter kann ein Abgasstrom variiert und auf diese Weise ebenfalls die Wärmebilanz der Schmelzflusselektrolysezelle beeinflusst werden. Ein Erhöhen des Abgasstromes vergrößert einen Wärmeaustrag während eine Reduzierung des Abgasstromes wie eine Isolierung wirkt.In summary, it can be stated that the heat in the fused salt electrolysis cell is mainly generated in the area of the anode-cathode distance. A reduction in the distance when the amperage increases and an increase in the distance when the amperage is reduced represents a first measure for regulating the heat balance. This varies the ohmic resistance of the fused-salt electrolysis cell, which is within certain limits, in particular due to a minimum distance between anode and aluminum pool as well as a energy-efficient processes are determined is possible. In addition, it is possible to use optional heat exchangers, for example on the side walls of the fused metal electrolysis cell, to dissipate heat from the fused flow electrolysis cell and to supply it if the energy provided by the power grid should otherwise not allow the fused flow electrolysis process to be maintained. Furthermore, an exhaust gas flow can be varied and in this way the heat balance of the fused-salt electrolysis cell can also be influenced. An increase in the exhaust gas flow increases heat output, while a reduction in the exhaust gas flow acts as an insulation.

Auf diese Weise ist es möglich, eine Schmelzflusselektrolyseanlage, insbesondere eine Aluminiumelektrolyseanlage, ohne die Anforderung einer konstanten, aus dem Stromnetz zur Verfügung gestellten Stromstärke wirtschaftlich lohnend zu betreiben.In this way it is possible to use a melt flow electrolysis system, in particular an aluminum electrolysis system, without the requirement of a to operate a constant amperage made available from the power grid in an economically viable manner.

Figur 2 zeigt in einer schematischen Ansicht eine Schmelzflusselektrolyseanlage mit einer Schmelzflusselektrolysezelle 30. Die Schmelzflusselektrolysezelle 30 wird seitlich durch Zellenwände 32 begrenzt und weist darüber hinaus einen Zellenboden 34 auf, der gleichzeitig als Kathode für das Schmelzflusselektrolyseverfahren im Innern der Zelle 30 fungiert. Im Innern der Zelle 30 befindet sich eine von oben in die Zelle 30 hineinragende Anode 36 und die Schmelze 38, 35.1, die u. a. Kryolith und geschmolzenes Aluminium aufweist. Unmittelbar an den Zellenwänden 32 der Schmelzflusselektrolysezelle 30 ist in der in Figur 2 gezeigten Ausführungsform ein Wärmetauscher 39 angeordnet, durch den ein Fluid, wie z. B. Luft, CO2, Stickstoff oder eine Flüssigkeit geleitet wird. Der Wärmetauscher 39 ist dabei besonders bevorzugt über ein Leitungssystem 31 mit einem Wärmespeicher 33 verbunden, der beispielsweise durch einen konventionellen oder auch einen Latenzwärmespeicher gebildet sein kann. Figure 2 FIG. 12 shows a schematic view of a melt flow electrolysis system with a melt flow electrolysis cell 30. The melt flow electrolysis cell 30 is laterally bounded by cell walls 32 and also has a cell bottom 34, which at the same time functions as a cathode for the melt flow electrolysis process inside the cell 30. Inside the cell 30 there is an anode 36 protruding from above into the cell 30 and the melt 38, 35.1, which includes cryolite and molten aluminum, among other things. Immediately on the cell walls 32 of the fused metal electrolysis cell 30 is shown in FIG Figure 2 embodiment shown, a heat exchanger 39 is arranged through which a fluid, such as. B. air, CO 2 , nitrogen or a liquid is passed. The heat exchanger 39 is particularly preferably connected via a line system 31 to a heat store 33, which can be formed, for example, by a conventional or also a latency heat store.

Im Fall einer hohen Leistungsaufnahme der Schmelzflusselektrolysezelle 30 wird im Innern der Zelle durch die Elektrolyse eine große Menge Wärmeenergie freigesetzt, die von der Zelle über ihre Seitenwände 32 und den Zellenboden 34 sowie über Abgase nach oben abgegeben wird. Die gewünschte abgegebene Wärme wird dabei so bemessen, dass an der Innenseite der Zellenwände 32 Krusten (Borde) 35.2 der erstarrten Schmelze 35.1 als Schutzschicht gebildet werden. Die Krusten 35.2 variieren lediglich in ihrer Dicke in Abhängigkeit von der Wärmebilanz der Schmelzflusselektrolysezelle.In the case of a high power consumption of the fused-salt electrolysis cell 30, a large amount of thermal energy is released inside the cell by the electrolysis, which is released from the cell via its side walls 32 and the cell bottom 34 and via exhaust gases upwards. The desired heat emitted is measured in such a way that crusts (rims) 35.2 of the solidified melt 35.1 are formed as a protective layer on the inside of the cell walls 32. The crusts 35.2 only vary in their thickness as a function of the heat balance of the fused metal electrolysis cell.

Sofern es nötig werden sollte, dass aufgrund einer zu geringen elektrischen Leistungsaufnahme durch die Schmelzflusselektrolysezelle Wärme von außen zugeführt oder mit anderen Worten die Menge aus der Zelle abgeführter Wärme reduziert werden muss, um die Krusten 35.2 nicht zu groß werden zu lassen, kann Wärme aus dem Wärmespeicher 33 durch das Leitungssystem 31 zum Wärmetauscher 39 geleitet werden. Dadurch kann das Innere der Schmelzflusselektrolysezelle über die Zellenwände 32 effektiv beheizt werden, indem weniger Wärme nach außen abgestrahlt wird, weil der Temperaturunterschied zwischen dem Innern der Zelle und der Außenseite der Zellenwände 32 verringert wird, und dadurch das Erstarren der Schmelze gehemmt wird. Derselbe Effekt wird über eine Variation der nach oben abgesaugten oder zurückgehaltenen Abgase erzielt.If it should become necessary that due to insufficient electrical power consumption by the Fused metal electrolysis cell, heat is supplied from the outside or, in other words, the amount of heat removed from the cell has to be reduced in order not to let the crusts 35.2 become too large, heat can be conducted from the heat store 33 through the line system 31 to the heat exchanger 39. As a result, the inside of the fused metal electrolysis cell can be effectively heated via the cell walls 32 by less heat being radiated to the outside, because the temperature difference between the inside of the cell and the outside of the cell walls 32 is reduced, and the solidification of the melt is thereby inhibited. The same effect is achieved by varying the exhaust gases sucked up or retained.

Eine Regelungseinrichtung 37 ist dazu ausgestaltet, die Zelle der Schmelzflusselektrolyseanlage derart zu betreiben, dass ihre Wärmebilanz geregelt wird, wie oben beschrieben wurde. Hierfür umfasst die Schmelzflusselektrolysezelle eine Vielzahl von (nicht gezeigten) Thermoelementen in ihren Seitenwänden, dem Boden und auch im Bereich ihrer sich oben an die Schmelzflusselektrolysezelle anschließenden Abluftführung. Die von diese Thermoelementen erfassten Messergebnisse werden der Regelungseinrichtung 37 zugeführt und dort zur Regelung des Betriebs der Schmelzflusselektrolysezelle ausgewertet.A control device 37 is designed to operate the cell of the melt flow electrolysis system in such a way that its heat balance is controlled, as has been described above. For this purpose, the fusible electrolysis cell comprises a multiplicity of thermocouples (not shown) in its side walls, the bottom and also in the area of its exhaust air duct adjoining the fusible electrolysis cell at the top. The measurement results recorded by these thermocouples are fed to the regulating device 37 and evaluated there to regulate the operation of the melt-flow electrolysis cell.

Durch den Betrieb einer solchen Schmelzflusselektrolyseanlage kann neben der Erzeugung von beispielsweise Aluminium auch noch das Stromnetz trotz Einspeisung volatiler Energiequellen stabil gehalten werden, ohne auf spezielle (derzeit nicht in ausreichendem Umfang verfügbarer) Speicher und dergleichen zurückgreifen zu müssen.By operating such a melt-flow electrolysis system, in addition to the production of aluminum, for example, the power grid can also be kept stable despite the infeed of volatile energy sources, without having to resort to special (currently insufficiently available) storage devices and the like.

Claims (15)

  1. Control method for operating a cell of a molten salt electrolysis system, in particular for producing aluminium,
    wherein a first controlled variable is an energy balance of the cell, which takes into account the electrical energy that enters the molten salt electrolysis cell and the heat energy that leaves the molten salt electrolysis cell, and
    wherein a second controlled variable is a thermal state of the cell.
  2. Control method according to claim 1, wherein a thermocouple and/or a device for determining a volumetric flow rate of exhaust air from the cell and/or a device for determining a volumetric flow rate of a heat transfer fluid in a heat exchanger on the cell is or are used as a measuring element for determining the first controlled variable.
  3. Control method according to claim 1 or 2, wherein the cell comprises side walls, a floor and an exhaust air duct,
    wherein thermocouples arranged on or in at least one of the side walls, the floor or the exhaust air duct, preferably on or in all side walls and the floor and particularly preferably also on or in the exhaust air duct are used as measuring elements for determining the first controlled variable.
  4. Control method according to any of the preceding claims, wherein at least one heat exchanger and/or at least one exhaust gas flow valve and/or a chemical composition of the melt, in particular an AlF3 dose, and/or at least one crossbar for positioning at least one anode in the cell are used as a final control element for influencing a heat input and/or a heat output.
  5. Control method according to any of the preceding claims, wherein an input of material to be melted, in particular aluminium oxide and cryolite, and/or an output of molten material, in particular aluminium, and/or a change in an electrolysis current strength is or are taken into account as a disturbance variable.
  6. Control method according to any of the preceding claims, wherein a third controlled variable is a chemical state of the cell.
  7. Control method according to any of the preceding claims, wherein a current used for operating the cell is supplied from a power grid.
  8. Molten salt electrolysis system, in particular for producing aluminium, comprising a molten salt electrolysis cell,
    characterised in that the
    molten salt electrolysis system comprises a control device, which is designed to carry out a control method according to any of the preceding claims.
  9. Molten salt electrolysis system according to claim 8, in particular comprising a heat exchanger for influencing a heat input or heat output by means of a heat transfer fluid on at least one outer surface of the molten salt electrolysis cell,
    wherein the molten salt electrolysis cell comprises a thermocouple and/or a measuring device for determining a volumetric flow rate of exhaust air from the molten salt electrolysis cell and/or a measuring device for determining a volumetric flow rate of the heat transfer fluid in the heat exchanger on the molten salt electrolysis cell.
  10. Molten salt electrolysis system according to claim 8 or 9, wherein the molten salt electrolysis cell comprises side walls, a floor and an exhaust air duct,
    wherein thermocouples are arranged on or in at least one of the side walls, the floor or the exhaust air duct, preferably on or in all side walls and the floor and particularly preferably also on or in the exhaust air duct.
  11. Molten salt electrolysis system according to any of claims 8 to 10, comprising
    a heat exchanger for influencing a heat input or heat output by means of a heat transfer fluid on at least one outer surface of the molten salt electrolysis cell and/or
    an adjustable exhaust gas flow valve for influencing a volumetric flow rate of an exhaust gas from the molten salt electrolysis cell and/or
    a device for altering a chemical composition of the melt, in particular for altering a dose of AlF3 in the melt, and/or
    a crossbar for positioning an anode in the molten salt electrolysis cell.
  12. Molten salt electrolysis system according to any of claims 8 to 11, comprising a device for determining a mass of material to be melted, in particular aluminium oxide and cryolite, introduced into the molten salt electrolysis cell, and/or a device for determining a mass of molten material, in particular aluminium, discharged from the molten salt electrolysis cell.
  13. Molten salt electrolysis system according to any of claims 8 to 12, wherein the molten salt electrolysis system is connected to a power grid in order to be supplied with electrical energy for the molten salt electrolysis.
  14. Use of a control method according to claim 7 or a molten salt electrolysis system according to claim 13 for compensating for fluctuations in the feed-in of energy into the power grid.
  15. Use according to claim 14, wherein the energy fed in comes from a volatile power source, in particular a wind turbine and/or a solar plant.
EP16177980.6A 2016-07-05 2016-07-05 Molten salt electrolysis system and control method for operation of the same Active EP3266904B1 (en)

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CN112210793B (en) * 2020-10-19 2022-06-10 郑州轻冶科技股份有限公司 Aluminum electrolytic cell with heat pipe heat exchanger on side part
CN115029735B (en) * 2022-05-26 2024-01-30 中南大学 Aluminum electrolysis heat balance regulating and controlling device and method for new energy consumption

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