Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/60—Constructional parts of cells
  • C25B9/65—Means for supplying current; Electrode connections; Electric inter-cell connections
  • C25B9/66—Electric inter-cell connections including jumper switches

Definitions

• the present invention relates to devices for short-circuiting devices consuming electricity connected in series in a high intensity electrical circuit and more particularly a device for short-circuiting an electrolysis cell.
• High intensity electrical circuits are used in various applications such as electrolysis rooms, test stations or electric ovens. These circuits generally carry intensities ranging from 10 to 400 kiloamperes (A).
• A kiloamperes
• the cell which must be stopped is generally short-circuited, which makes it possible to keep the other cells in operation.
• the short-circuiting operation consists in coming to connect a short-circuiting circuit or short-circuiter, to the cathode of the previous cell (i.e. to the current output electrode) and to the anode of the next cell ( ie at the current input electrode) After closing the short-circuit switch, the high-intensity electric current supplying the cells flows into the latter, the cell is then no longer fed
• the traditional solution is to inject neutralizing products into the cell, during the short-circuiting. It may for example be bisulfite. This operation obliges operators to intervene in dangerous conditions by discharging several hundred liters of products into the cell through an orifice.
• the object of the invention is to overcome these drawbacks by providing a short-circuiting device which makes it possible to cancel the reverse current which is created in a cell. electrolysis when it is short-circuited and which therefore makes it possible to avoid degradation of the electrodes, while maintaining polarization in the cell.
• the invention relates to a device for short-circuiting an electrolysis cell, connected in series to at least one other electrolysis cell in an electrolysis room, intended to be connected to the terminals of the electrolysis cell of so that it is no longer supplied.
• This device comprises at least one variable resistor whose value is defined so that the voltage across the terminals of the cell has a value at least equal to a predetermined minimum value making it possible to prevent the formation of a reverse current to the inside the cell, this reverse current being due to an electromotive force produced inside the cell, when the latter is no longer supplied.
• FIG. 1 represents the assembly of an electrolysis room composed of several electrolysis cells connected in series.
• FIG. 2 represents the evolution of the current circulating in the electrolysis cell as a function of the voltage exerted across its terminals.
• FIG. 3 represents the evolution of the reverse voltage occurring in the electrolysis cell, when the latter is short-circuited, as a function of time.
• FIG. 4 represents the short-circuiting device according to the invention connected to the terminals of the electrolysis cell.
• An electrolysis room is generally made up of electrolysis cells 10, the number of which generally varies between 20 and 200, connected in series via an electrical circuit 12.
• the current which supplies the electrolysis cells is a direct current obtained thanks to a rectifier 14. This rectifier transforms the medium voltage alternating current which it receives via a connection 16, in a low voltage direct current enabling the electrolysis cells to be supplied.
• a high intensity direct current of constant and adjustable value is applied to the electrolysis cells.
• the behavior of the electrolysis cells implies that its resistance varies as a function of the voltage U which is applied across the terminals of these cells.
• the current I supplying the electrolysis cells varies as a function of the voltage. Indeed, when the value of the voltage is between 0 and an X value, the current does not pass through the electrolysis cells.
• the intensity of the current flowing in the cell increases to reach a maximum value Z, corresponding to the value of the current supplied by the rectifier, when the voltage has a value Y. For voltage values greater than Y, the intensity of the current flowing in the cell remains at its maximum value.
• the operation of the electrolysis cell is therefore optimal when the voltage has a value equal to Y, that is to say when the value of the current which passes through the cell is equal to that of the current supplied by the rectifier.
• the X and Y voltage values are different depending on the type of electrolysis cell used.
• the voltage value X at the terminals of the cell allowing current to flow in the cell is for example 2.35 volts (V).
• the value Y of voltage at the terminals of the cell enabling the totality of the current supplied by the rectifier flowing in the cell to be obtained, is 3.5 V.
• the voltage at the terminals of the cell is less than 2.35 V , the cell behaves like a capacity which discharges This phenomenon is however transitory.
• this value can be for example 1.8 V
• a short-circuiting voltage, or bias voltage at the terminals of the electrolysis cell, the value of which is at least U max, ie 1.8 V in the example above.
• this voltage must not have a value greater than 2.35 V in order not to trigger electrolysis.
• FIG. 4 represents the short-circuiting device according to the invention, in a preferred embodiment.
• a short-circuiting device composed of a variable resistor 20, a detector 22 and a controller 24 is connected to the terminals of this cell.
• the detector 22 regularly measures the voltage across the terminals of cell 18, a voltage which is equal to RI, R being the variable resistance of the short-circuiting circuit and I the intensity of the current supplied by the rectifier.
• the short-circuiting voltage must have a minimum value of 1.8 V and a maximum value of 2.35 V
• the value of the voltage detected by the detector 22 is supplied to the controller 24.
• the latter acts on the variable resistor 20 and varies its value so that the voltage at the terminals of the cell is always between U max and X, it is at say 1.8 volts and 2.35 volts in the example above.
• Another advantage of being able to modify the value of the resistance at the terminals of the electrolysis cell by means of the short-circuiting device resides in the case where the intensity of the current supplied to the electrolysis room by the rectifier is deliberately modified by technical staff. Indeed, the intensity of the high intensity current supplying an electrolysis room can be fixed at a value between 70 and 140 kiloamperes (kA), as required. Thanks to the short-circuiting device according to the invention, the voltage at the terminals of the short-circuited electrolysis cells will always be sufficient to avoid the formation of reverse current and therefore the degradation of the electrodes regardless of the intensity of the current supplying the electrolysis room.
• the variable resistance of the short-circuiting device can take various forms.
• the resistance can be adjusted continuously as a function of variations in intensity.
• the variable resistor can also consist of several resistors connected in parallel. According to a particular embodiment, these resistors are connected or disconnected so as to vary the value of the overall resistance. Indeed, knowing that the overall resistance decreases when the number of resistors connected in parallel increases and that it increases when their number decreases, it is easy to vary the overall resistance to adapt its value to that of the intensity in order to obtain a constant voltage across the electrolysis cell.
• the short-circuiting technique is only used temporarily. In fact, in the hours following the short-circuiting, the tank is generally emptied of its electrolyte, in order to undergo the maintenance operation. There is no longer any risk of degradation of the electrodes.
• the device according to the invention therefore makes it possible to isolate one or more electrolysis cells, without immobilizing the entire electrolysis room, which would have a very high cost. Compared to conventional short-circuiting devices, it makes it possible to maintain a voltage at the terminals of the isolated cells which is large enough to prevent the production of a reverse current which would degrade the electrodes. Thus, cell maintenance is much more flexible since there is no longer any risk of degradation over time. In addition, this system makes it possible, thanks to its variable resistance, to maintain a predetermined constant voltage value, despite voluntary or involuntary variations in intensity.
• this device makes it possible to overcome the constraints created by the use of dangerous materials such as asbestos still necessary to protect the electrodes of the electrolysis cells.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

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• 2000
  • 2000-02-11 FR FR0001925A patent/FR2805098B1/fr not_active Expired - Fee Related
• 2001
  • 2001-02-09 EP EP01907741A patent/EP1257689A1/de not_active Withdrawn
  • 2001-02-09 AU AU2001235638A patent/AU2001235638A1/en not_active Abandoned
  • 2001-02-09 WO PCT/FR2001/000375 patent/WO2001059184A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

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