EP0396174A1 - Process for positioning an anode set in a mercury cathode electrolysis cell wherein chlorine is produced - Google Patents
Process for positioning an anode set in a mercury cathode electrolysis cell wherein chlorine is produced Download PDFInfo
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- EP0396174A1 EP0396174A1 EP90201008A EP90201008A EP0396174A1 EP 0396174 A1 EP0396174 A1 EP 0396174A1 EP 90201008 A EP90201008 A EP 90201008A EP 90201008 A EP90201008 A EP 90201008A EP 0396174 A1 EP0396174 A1 EP 0396174A1
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- anode unit
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B15/00—Operating or servicing cells
- C25B15/04—Regulation of the inter-electrode distance
Definitions
- the present invention relates to a method for adjusting the position of the anodes in electrolysis cells with a horizontal mercury cathode, used for the production of chlorine by electrolysis of an aqueous solution of sodium chloride.
- the distance between the anodes and the cathode is an important parameter in the operation of electrolysis cells with a horizontal mercury cathode. Excessive distance damages the energy balance of the electrolysis operation, causing an unnecessary loss of electrical energy by the Joule effect in the electrolyte. A too short distance also harms the energy balance, causing a drop in the electrochemical yield of the electrode reactions (the drop in yield being due to a reduction, in contact with mercury, of part of the chlorine generated at the anodes). It should also be avoided that one or the other anode occasionally comes into contact with the mercury cathode, because the short-circuit which would result therefrom could cause serious degradation at the anode, mainly in the case of titanium anodes carrying an active coating based on noble metal oxide.
- the causes of an untimely variation of the anode-cathode distances or of a fortuitous contact between an anode and mercury are numerous; they may reside in particular in a deformation or wear of the anode, the formation of agglomerates of large mercury (sometimes called "mercury butter") adhering to the bottom of the cell or floating on the surface of mercury, an untimely variation of the mercury level in the cell, an incidental turbulence occurring in the flow of mercury.
- agglomerates of large mercury sometimes called "mercury butter”
- the invention provides a method which improves on the known method described above, by involving the anode imperfections in the adjustment of the anode-cathode distances of the mercury cells.
- the invention therefore relates to a method for positioning an anode unit in a mercury cathode electrolysis cell in which chlorine is produced on an active area of the anode unit by electrolysis of a sodium chloride brine; according to the invention, the anode unit is brought into a reference position for which the electrical resistance of the brine layer located between the active area of the anode unit and the cathode is equal to a set value, we temporarily set aside the anodic unit of the reference position, from a defined distance, the corresponding variation of the electrical resistance of the brine layer is measured and the position of the anodic unit is corrected when the measured variation exceeds a threshold value.
- the anode unit can be an individual anode or a group of anodes displaceable together with respect to the mercury cathode, for example a group of anodes fixed together, in derivation, to a rigid and displaceable current collector.
- the active zone of the anode unit is the zone thereof, which effectively participates in the electrochemical reaction of oxidation of chloride ions during electrolysis.
- the reference position of the anode unit is a physically indeterminate position, defined by an imposed value (set value) of the electrical resistance of the brine layer located directly above its active area.
- the set value is the magnitude of the electrical resistance of the electrolyte layer under the active area of a reference anode during electrolysis, when this reference anode occupies a predetermined theoretical position for which the user of the cell electrolysis considers that its operation is optimum.
- the reference anode is an ideal anode, free from flatness defects and strictly parallel to the sheet of mercury forming the cathode.
- a new anode of the cell is chosen for the reference anode.
- the theoretical position therefore depends on the geometry of the reference anode and the density of the electrolysis current, and it must be determined in each particular case by a routine experimental study, depending on the operating conditions of the cell. electrolysis.
- the electrical resistance of the brine layer between the active area of the anode unit and the cathode is measured, and the position of the anode unit is adjusted so that the resistance measured equals the setpoint defined above.
- the measurement of the electrical resistance can be obtained by any suitable means, for example by means of an ohmmeter or from a measurement of the intensity of the electric current passing through the anode unit during the operation of the cell and of a measure of the difference in electrical potential between this unit anode and the mercury cathode.
- the technique described in patent BE-A-668236 is advantageously used.
- the corresponding variation in the electrical resistance of the brine layer is measured under the active zone of the anode unit and it is compared to a threshold value.
- the threshold value is the electrical resistance that a layer of brine free of chlorine bubbles would have, located under the active zone of the anode unit and whose thickness is equal to the aforementioned defined distance.
- the method according to the invention is based on the observation that, all other things remaining equal, the electrical resistivity of the layer of brine interposed between an anode and the cathode increases when this layer of brine is charged with a substantial amount of chlorine gaseous.
- the measurement of the variation in resistance (consecutive to a momentary separation of the anode unit from its reference position) and its comparison with the threshold value are therefore an indication of the density of bubbles.
- chlorine in the brine layer under the anode unit and thus constitute a control of the position of the anode unit in the electrolysis cell.
- the position of the anode unit is corrected, by increasing the anode-cathode distance by an imposed value, generally arbitrary.
- the anode unit after having corrected the position of the anode unit in the manner described above, it is subjected to a second control. For this purpose, it is temporarily removed from its corrected position, by a distance equal to the aforementioned defined distance, the corresponding variation in resistance is measured and an additional correction is made to the position of the unit. anodic, if the measured variation exceeds the threshold value. If necessary, the anode unit can thus be subjected to several successive corrections, until the resistance variation no longer exceeds the threshold value.
- the observation that after several successive corrections, it is not possible to reach a resistance variation less than the threshold value, is an indication that the anode unit subjected to the adjustment has reached an excessive level of imperfection.
- a defined number of successive corrections is fixed, beyond which the anode unit is put out of service, if the measured resistance variation remains greater than the threshold value.
- the cell was equipped with a mixture of new and used anodes.
- electrolysis of a brine containing approximately 230 g was carried out.
- sodium chloride per kg the temperature in the cell being about 50 to 70 ° C. It has been calculated that at this temperature, the electrical resistance of a layer of brine with a surface area of 1 m2 and a thickness of 1 mm (above the mercury) was approximately 30 ⁇ Ohm. This value was therefore chosen as the resistance threshold value, in the application of the method according to the invention.
- each anode was positioned individually in the cell, by means of the method and of the adjustment installation described in patent BE-A-668236.
- each anode was gradually lowered towards the cathode, the electrical resistance of the underlying brine layer was simultaneously measured and the anode (reference position) was stabilized as soon as the resistance measured was equal to a predetermined set value.
- the average energy consumption and the average anode current efficiency were calculated.
- the electrolysis voltage has been corrected to bring the temperature in the cell back to the normalized value of 60 ° C.
- the setpoint value selected corresponded to the resistance of a 2 mm layer of brine, under a new anode.
- the cell operated continuously with the anodes set to this setpoint.
- the operation of the cell was adjusted to achieve in it a cathode current density equal to 7.6 kA / m2.
- the brine temperature stabilized at around 68 ° C.
- the test lasted twelve days. The following results were obtained: - average energy consumption: 3,190 kWh / kg of chlorine; - average current efficiency: 93.6%.
- Example 1 The test of Example 1 was repeated, with a density of cathodic current equal to 4.3 kA / m2.
- the temperature of the brine subjected to electrolysis was approximately 55 ° C.
- the trial lasted 3 days.
- the cell operated under a cathodic current density of 7.6 kA / m2 for 14 days, the temperature in the cell being stabilized at 60 ° C. - Average energy consumption: 3.167 kWh / kg of chlorine; - Average current efficiency: 90.2%.
- the cell operated under a cathodic current density of 4.3 kA / m2, for 3 days, the temperature in the cell being stabilized at 54 ° C. - Average energy consumption: 2.992 kWh / kg of chlorine; - Average current efficiency: 87.9%.
- each anode was subjected to a control test, comprising the following successive steps: - raise the anode by 1 mm, - measure the resulting increase in the electrical resistance of the brine layer under the anode, - compare the increase in electrical resistance to the imposed threshold value (30 ⁇ Ohm.m2 / S, where S is the area of the anode, expressed in m2), - lower the anode by 1 mm, if the increase in electrical resistance is equal to or less than the imposed threshold value.
- the control test revealed 19 anodes for which the increase in resistance was greater than the threshold value.
- the cell therefore operated with 19 anodes occupying a position corresponding to a theoretical anode-cathode distance of 2 mm (corrected anodes) and 161 anodes occupying a position corresponding to a theoretical anode-cathode distance of 1 mm (anodes maintained in the position reference).
- the trial lasted 45 days and resulted in the following results: - average energy consumption: 3,090 kWh / kg of chlorine; - average current efficiency: 92.5%.
- Example 5 The test of Example 5 was repeated, under the electrolysis conditions of Example 4 (current density: 4.3 kA / m2; temperature: 53 ° C; setpoint corresponding to an anode distance- 1 mm cathode in the case of a new anode). The following results were obtained: - average energy consumption: 2.945 kWh / kg of chlorine; - average current efficiency: 89.5
- Example 5 A test similar to that of Example 5 was carried out under the following conditions: - cathodic current density: 7.6 kA / m2; - setpoint corresponding to a theoretical anode-cathode distance of 0.7 mm, in the case of a new anode.
- the control test revealed 28 anodes for which the increase in electrical resistance was greater than the threshold value. These 28 anodes were therefore raised by 1 mm from the initial reference position.
- the test lasted five days and resulted in the following results: - average energy consumption: 3,034 kWh / kg of chlorine; - average current efficiency: 91.2%.
- Example 7 The test of Example 7 was repeated with a cathode current density of 4.3 kA / m2.
- Table I relates to the electrolysis tests at a current density of 7.6 kA / m2 (examples 1, 3, 5, 7), and Table II relates to the electrolysis tests at a current density of 4, 3 kA / m2 (examples 2, 4, 6, 8).
- Table I Example No. Energy consumption (kWh / kg chlorine) Current efficiency (%) 1 3,190 93.6 3 3.167 90.2 5 3,090 92.5 7 3.034 91.2
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Abstract
Description
La présente invention a pour objet un procédé pour régler la position des anodes dans les cellules d'électrolyse à cathode horizontale de mercure, utilisées pour la production de chlore par électrolyse d'une solution aqueuse de chlorure de sodium.The present invention relates to a method for adjusting the position of the anodes in electrolysis cells with a horizontal mercury cathode, used for the production of chlorine by electrolysis of an aqueous solution of sodium chloride.
La distance séparant les anodes de la cathode est un paramètre important du fonctionnement des cellules d'électrolyse à cathode horizontale de mercure. Une distance excessive nuit au bilan énergétique de l'opération d'électrolyse, en occasionnant une perte inutile d'énergie électrique par effet Joule dans l'électrolyte. Une distance trop faible nuit aussi au bilan énergétique, en provoquant une chute du rendement électrochimique des réactions d'électrodes (la chute de rendement étant imputable à une réduction, au contact du mercure, d'une partie du chlore généré aux anodes). Il convient par ailleurs d'éviter que l'une ou l'autre anode entre occasionnellement en contact avec la cathode de mercure, car le court-circuit qui en résulterait serait susceptible d'occasionner des dégradations graves à l'anode, principalement dans le cas d'anodes en titane portant un revêtement actif à base d'oxyde de métal noble. Les causes d'une variation intempestive des distances anode-cathode ou d'un contact fortuit entre une anode et le mercure sont nombreuses; elles peuvent résider notamment dans une déformation ou une usure de l'anode, la formation d'agglomérats de gros mercure (appelé parfois "beurre de mercure") adhérant à la sole de la cellule ou flottant à la surface du mercure, une variation intempestive du niveau du mercure dans la cellule, une turbulence fortuite survenant dans l'écoulement du mercure. Pour optimiser le fonctionnement des cellules à mercure, il est dès lors nécessaire de contrôler périodiquement la position des anodes dans les cellules d'électrolyse et d'opérer éventuellement un ajustement des anodes.The distance between the anodes and the cathode is an important parameter in the operation of electrolysis cells with a horizontal mercury cathode. Excessive distance damages the energy balance of the electrolysis operation, causing an unnecessary loss of electrical energy by the Joule effect in the electrolyte. A too short distance also harms the energy balance, causing a drop in the electrochemical yield of the electrode reactions (the drop in yield being due to a reduction, in contact with mercury, of part of the chlorine generated at the anodes). It should also be avoided that one or the other anode occasionally comes into contact with the mercury cathode, because the short-circuit which would result therefrom could cause serious degradation at the anode, mainly in the case of titanium anodes carrying an active coating based on noble metal oxide. The causes of an untimely variation of the anode-cathode distances or of a fortuitous contact between an anode and mercury are numerous; they may reside in particular in a deformation or wear of the anode, the formation of agglomerates of large mercury (sometimes called "mercury butter") adhering to the bottom of the cell or floating on the surface of mercury, an untimely variation of the mercury level in the cell, an incidental turbulence occurring in the flow of mercury. To optimize the functioning of the mercury cells, it is therefore necessary to periodically check the position of the anodes in the electrolysis cells and possibly to make an adjustment. anodes.
Dans le brevet BE-A-668236 (IMPERIAL CHEMICAL INDUSTRIES LIMITED), on décrit un procédé pour régler la position d'une anode dans une cellule à cathode de mercure, selon lequel on mesure la résistance électrique de la couche de saumure de chlorure de sodium séparant l'anode de la cathode, on compare la valeur mesurée de la résistance à une valeur de consigne et on déplace l'anode jusqu'à lui faire occuper une position de référence pour laquelle ces deux valeurs s'égalent.In patent BE-A-668236 (IMPERIAL CHEMICAL INDUSTRIES LIMITED), a method is described for adjusting the position of an anode in a mercury cathode cell, according to which the electrical resistance of the chloride layer of brine chloride is measured. sodium separating the anode from the cathode, the measured value of the resistance is compared to a set value and the anode is moved until it occupies a reference position for which these two values are equal.
Dans ce procédé connu, il est difficile, voire impossible, de tenir compte des imperfections des anodes, dans le calcul de la valeur de consigne. Ces imperfections comprennent des zones locales dépourvues du revêtement actif pour la réaction d'électrode, des défauts de planéité, un manque de parallélisme avec la nappe de mercure. Elles sont notamment liées à l'âge des anodes et à leur degré d'usure, et il est pratiquement impossible de déceler leur apparition et leur évolution pendant l'électrolyse et de chiffrer leur incidence sur la valeur de consigne précitée.In this known method, it is difficult, if not impossible, to take account of the imperfections of the anodes, in calculating the set value. These imperfections include local areas lacking the active coating for the electrode reaction, flatness defects, a lack of parallelism with the mercury sheet. They are notably linked to the age of the anodes and to their degree of wear, and it is practically impossible to detect their appearance and their evolution during electrolysis and to quantify their incidence on the aforementioned reference value.
L'invention fournit un procédé qui perfectionne le procédé connu décrit plus haut, en faisant intervenir les imperfections des anodes dans le réglage des distances anode-cathode des cellules à mercure.The invention provides a method which improves on the known method described above, by involving the anode imperfections in the adjustment of the anode-cathode distances of the mercury cells.
L'invention concerne dès lors un procédé pour positionner une unité anodique dans une cellule d'électrolyse à cathode de mercure dans laquelle on produit du chlore sur une zone active de l'unité anodique par électrolyse d'une saumure de chlorure de sodium; selon l'invention, on amène l'unité anodique dans une position de référence pour laquelle la résistance électrique de la couche de saumure située entre la zone active de l'unité anodique et la cathode est égale à une valeur de consigne, on écarte provisoirement l'unité anodique de la position de référence, d'une distance définie, on mesure la variation correspondante de la résistance électrique de la couche de saumure et on corrige la position de l'unité anodique lorsque la variation mesurée excède une valeur de seuil.The invention therefore relates to a method for positioning an anode unit in a mercury cathode electrolysis cell in which chlorine is produced on an active area of the anode unit by electrolysis of a sodium chloride brine; according to the invention, the anode unit is brought into a reference position for which the electrical resistance of the brine layer located between the active area of the anode unit and the cathode is equal to a set value, we temporarily set aside the anodic unit of the reference position, from a defined distance, the corresponding variation of the electrical resistance of the brine layer is measured and the position of the anodic unit is corrected when the measured variation exceeds a threshold value.
Dans le procédé selon l'invention, l'unité anodique peut être une anode individuelle ou un groupe d'anodes déplaçables ensemble vis-à-vis de la cathode de mercure, par exemple un groupe d'anodes fixées ensemble, en dérivation, à un collecteur de courant rigide et déplaçable.In the process according to the invention, the anode unit can be an individual anode or a group of anodes displaceable together with respect to the mercury cathode, for example a group of anodes fixed together, in derivation, to a rigid and displaceable current collector.
La zone active de l'unité anodique est la zone de celle-ci, qui participe effectivement à la réaction électrochimique d'oxydation des ions chlorure pendant l'électrolyse.The active zone of the anode unit is the zone thereof, which effectively participates in the electrochemical reaction of oxidation of chloride ions during electrolysis.
La position de référence de l'unité anodique est une position physiquement indéterminée, définie par une valeur imposée (valeur de consigne) de la résistance électrique de la couche de saumure située à l'aplomb de sa zone active.The reference position of the anode unit is a physically indeterminate position, defined by an imposed value (set value) of the electrical resistance of the brine layer located directly above its active area.
La valeur de consigne est la grandeur de la résistance électrique de la couche d'électrolyte sous la zone active d'une anode de référence pendant l'électrolyse, lorsque cette anode de référence occupe une position théorique prédéterminée pour laquelle l'utilisateur de la cellule d'électrolyse estime que le fonctionnement de celle-ci est optimum. En principe, l'anode de référence est une anode idéale, exempte de défaut de planéité et rigoureusement parallèle à la nappe de mercure formant la cathode. En pratique, on choisit, pour l'anode de référence, une anode neuve de la cellule. La position théorique dépend dès lors de la géométrie de l'anode de référence et de la densité du courant d'électrolyse, et elle doit être déterminée dans chaque cas particulier par une étude expérimentale de routine, en fonction des conditions de fonctionnement de la cellule d'électrolyse.The set value is the magnitude of the electrical resistance of the electrolyte layer under the active area of a reference anode during electrolysis, when this reference anode occupies a predetermined theoretical position for which the user of the cell electrolysis considers that its operation is optimum. In principle, the reference anode is an ideal anode, free from flatness defects and strictly parallel to the sheet of mercury forming the cathode. In practice, a new anode of the cell is chosen for the reference anode. The theoretical position therefore depends on the geometry of the reference anode and the density of the electrolysis current, and it must be determined in each particular case by a routine experimental study, depending on the operating conditions of the cell. electrolysis.
Pour amener l'unité anodique dans la position de référence définie plus haut, on mesure la résistance électrique de la couche de saumure entre la zone active de l'unité anodique et la cathode, et on ajuste la position de l'unité anodique pour que la résistance mesurée égale la valeur de consigne définie plus haut. La mesure de la résistance électrique peut être obtenue par tout moyen adéquat, par exemple au moyen d'un ohmmètre ou à partir d'une mesure de l'intensité du courant électrique traversant l'unité anodique pendant le fonctionnement de la cellule et d'une mesure de la différence de potentiel électrique entre cette unité anodique et la cathode de mercure. On utilise avantageusement la technique décrite dans le brevet BE-A-668236 (IMPERIAL CHEMICAL INDUSTRIES LIMITED).To bring the anode unit to the reference position defined above, the electrical resistance of the brine layer between the active area of the anode unit and the cathode is measured, and the position of the anode unit is adjusted so that the resistance measured equals the setpoint defined above. The measurement of the electrical resistance can be obtained by any suitable means, for example by means of an ohmmeter or from a measurement of the intensity of the electric current passing through the anode unit during the operation of the cell and of a measure of the difference in electrical potential between this unit anode and the mercury cathode. The technique described in patent BE-A-668236 (IMPERIAL CHEMICAL INDUSTRIES LIMITED) is advantageously used.
Conformément à l'invention, après avoir amené l'unité anodique dans la position de référence, on l'écarte provisoirement de cette position, d'une distance définie, on mesure la variation correspondante de la résistance électrique de la couche de saumure sous la zone active de l'unité anodique et on la compare à une valeur de seuil.According to the invention, after having brought the anode unit to the reference position, it is temporarily removed from this position, by a defined distance, the corresponding variation in the electrical resistance of the brine layer is measured under the active zone of the anode unit and it is compared to a threshold value.
La valeur de seuil est la résistance électrique qu'aurait une couche de saumure exempte de bulles de chlore, située sous la zone active de l'unité anodique et dont l'épaisseur est égale à la distance définie précitée.The threshold value is the electrical resistance that a layer of brine free of chlorine bubbles would have, located under the active zone of the anode unit and whose thickness is equal to the aforementioned defined distance.
Le procédé selon l'invention est fondé sur l'observation que, toutes autres choses restant égales, la résistivité électrique de la couche de saumure interposée entre une anode et la cathode augmente lorsque cette couche de saumure est chargée d'une quantité substantielle de chlore gazeux. Dans le procédé selon l'invention, la mesure de la variation de résistance (consécutive à un écartement momentané de l'unité anodique de sa position de référence) et sa comparaison avec la valeur de seuil sont dès lors une indication de la densité de bulles de chlore dans la couche de saumure sous l'unité anodique, et constituent de la sorte un contrôle de la position de l'unité anodique dans la cellule d'électrolyse. Conformément à l'invention, dès que la variation susdite de résistance excède la valeur de seuil, on corrige la position de l'unité anodique, en augmentant la distance anode-cathode d'une valeur imposée, généralement arbitraire.The method according to the invention is based on the observation that, all other things remaining equal, the electrical resistivity of the layer of brine interposed between an anode and the cathode increases when this layer of brine is charged with a substantial amount of chlorine gaseous. In the method according to the invention, the measurement of the variation in resistance (consecutive to a momentary separation of the anode unit from its reference position) and its comparison with the threshold value are therefore an indication of the density of bubbles. chlorine in the brine layer under the anode unit, and thus constitute a control of the position of the anode unit in the electrolysis cell. According to the invention, as soon as the above variation in resistance exceeds the threshold value, the position of the anode unit is corrected, by increasing the anode-cathode distance by an imposed value, generally arbitrary.
Dans un forme d'exécution particulière du procédé selon l'invention, après avoir corrigé la position de l'unité anodique de la manière exposée ci-dessus, on la soumet à un second contrôle. A cet effet, on l'écarte provisoirement de sa position corrigée, d'une distance égale à la distance définie précitée, on mesure la variation correspondante de la résistance et on procède à une correction supplémentaire de la position de l'unité anodique, si la variation mesurée excède la valeur de seuil. Au besoin, l'unité anodique peut être ainsi soumise à plusieurs corrections successives, jusqu'à ce que la variation de résistance n'excède plus la valeur de seuil. L'observation qu'après plusieurs corrections successives, il ne soit pas possible d'atteindre une variation de résistance inférieure à la valeur de seuil, est une indication que l'unité anodique soumise au réglage a atteint un niveau d'imperfection excessif. En pratique, on se fixe un nombre défini de corrections successives, au-delà duquel on met l'unité anodique hors service, si la variation de résistance mesurée reste supérieure à la valeur de seuil.In a particular embodiment of the method according to the invention, after having corrected the position of the anode unit in the manner described above, it is subjected to a second control. For this purpose, it is temporarily removed from its corrected position, by a distance equal to the aforementioned defined distance, the corresponding variation in resistance is measured and an additional correction is made to the position of the unit. anodic, if the measured variation exceeds the threshold value. If necessary, the anode unit can thus be subjected to several successive corrections, until the resistance variation no longer exceeds the threshold value. The observation that after several successive corrections, it is not possible to reach a resistance variation less than the threshold value, is an indication that the anode unit subjected to the adjustment has reached an excessive level of imperfection. In practice, a defined number of successive corrections is fixed, beyond which the anode unit is put out of service, if the measured resistance variation remains greater than the threshold value.
Le procédé selon l'invention se prête facilement à un fonctionnement automatique, et on peut avantageusement l'associer à l'installation de régulation automatique, décrite dans le brevet EP-B-85999 (SOLVAY & Cie).The method according to the invention easily lends itself to automatic operation, and it can advantageously be associated with the automatic regulation installation, described in patent EP-B-85999 (SOLVAY & Cie).
Toutes autres choses étant égales, on a trouvé que la correction de la position des unités anodiques d'une cellule d'électrolyse, conformément au procédé selon l'invention, améliore notablement les performances de la cellule. En particulier le bilan énergétique de l'électrolyse est optimisé.All other things being equal, it has been found that correcting the position of the anode units of an electrolysis cell, in accordance with the method according to the invention, significantly improves the performance of the cell. In particular, the energy balance of electrolysis is optimized.
L'intérêt de l'invention va ressortir de la description suivante de quelques essais d'électrolyse.The advantage of the invention will emerge from the following description of some electrolysis tests.
Les essais dont la description suit ont été effectués dans une cellule d'électrolyse à cathode horizontale de mercure, du type V 200 de SOLVAY & Cie, bien connue des praticiens (Chlorine, Its Manufacture, Properties and Uses - J.S. SCONCE, Reinhold Publishing Corporation, 1962, pages 187 à 189). La cellule était équipée de 180 anodes métalliques, du type de celles décrites dans le brevet BE-A-811155 (IMPERIAL CHEMICAL INDUSTRIES LTD) : les anodes étaient formées de lamelles horizontales en titane, portant un revêtement actif constitué d'un mélange homogène d'oxyde de ruthénium et d'oxyde de titane. Les lamelles étaient disposées dans la cellule de manière que leur tranche soit dirigée vers la nappe de mercure. La cellule était équipée d'un mélange d'anodes neuves et d'anodes usagées. Dans les essais, on a procédé à l'électrolyse d'une saumure contenant environ 230 g de chlorure de sodium par kg, la température dans la cellule étant d'environ 50 à 70°C. On a calculé qu'à cette température, la résistance électrique d'une couche de saumure de 1 m² de surface et de 1 mm d'épaisseur (au-dessus du mercure) était d'environ 30 µOhm. Cette valeur a dès lors été choisie comme valeur de seuil de la résistance, dans l'application du procédé selon l'invention.The tests, the description of which follows, were carried out in an electrolysis cell with a horizontal mercury cathode, of the V 200 type from SOLVAY & Cie, well known to practitioners (Chlorine, Its Manufacture, Properties and Uses - JS SCONCE, Reinhold Publishing Corporation , 1962, pages 187 to 189). The cell was equipped with 180 metal anodes, of the type described in patent BE-A-811155 (IMPERIAL CHEMICAL INDUSTRIES LTD): the anodes were formed from horizontal titanium lamellae, carrying an active coating consisting of a homogeneous mixture of ruthenium oxide and titanium oxide. The slats were arranged in the cell so that their edge was directed towards the sheet of mercury. The cell was equipped with a mixture of new and used anodes. In the tests, electrolysis of a brine containing approximately 230 g was carried out. sodium chloride per kg, the temperature in the cell being about 50 to 70 ° C. It has been calculated that at this temperature, the electrical resistance of a layer of brine with a surface area of 1 m² and a thickness of 1 mm (above the mercury) was approximately 30 μOhm. This value was therefore chosen as the resistance threshold value, in the application of the method according to the invention.
Dans les essais, on a positionné chaque anode individuellement dans la cellule, au moyen du procédé et de l'installation de réglage décrits dans le brevet BE-A-668236. A cet effet, la cellule étant en fonctionnement, on a descendu progressivement chaque anode vers la cathode, on a mesuré simultanément la résistance électrique de la couche de saumure sous-jacente et on a stabilisé l'anode (position de référence) dès que la résistance mesurée fut égale à une valeur de consigne prédéterminée.In the tests, each anode was positioned individually in the cell, by means of the method and of the adjustment installation described in patent BE-A-668236. For this purpose, the cell being in operation, each anode was gradually lowered towards the cathode, the electrical resistance of the underlying brine layer was simultaneously measured and the anode (reference position) was stabilized as soon as the resistance measured was equal to a predetermined set value.
Dans chaque essai, on a calculé la consommation énergétique moyenne et le rendement de courant anodique moyen. Pour le calcul de la consommation énergétique moyenne, la tension d'électrolyse a été corrigée pour ramener la température dans la cellule à la valeur normalisée de 60°C.In each test, the average energy consumption and the average anode current efficiency were calculated. For the calculation of the average energy consumption, the electrolysis voltage has been corrected to bring the temperature in the cell back to the normalized value of 60 ° C.
Dans les deux exemples dont la description suit, la valeur de consigne sélectionnée correspondait à la résistance d'une couche de saumure de 2 mm, sous une anode neuve. La cellule a fonctionné en permanence avec les anodes réglées sur cette valeur de consigne.In the two examples, the description of which follows, the setpoint value selected corresponded to the resistance of a 2 mm layer of brine, under a new anode. The cell operated continuously with the anodes set to this setpoint.
On a réglé le fonctionnement de la cellule pour réaliser dans celle-ci une densité de courant cathodique égale à 7,6 kA/m². La température de la saumure s'est stabilisée à environ 68°C. L'essai a duré douze jours. On a obtenu les résultats suivants :
- consommation énergétique moyenne : 3,190 kWh/kg de chlore;
- rendement de courant moyen : 93,6 %.The operation of the cell was adjusted to achieve in it a cathode current density equal to 7.6 kA / m². The brine temperature stabilized at around 68 ° C. The test lasted twelve days. The following results were obtained:
- average energy consumption: 3,190 kWh / kg of chlorine;
- average current efficiency: 93.6%.
On a répété l'essai de l'exemple 1, avec une densité de courant cathodique égale à 4,3 kA/m². La température de la saumure soumise à l'électrolyse s'est établie à environ 55°C. L'essai a duré 3 jours.
- Consommation énergétique moyenne : 2,988 kWh/kg de chlore;
- Rendement de courant moyen : 90,5 %.The test of Example 1 was repeated, with a density of cathodic current equal to 4.3 kA / m². The temperature of the brine subjected to electrolysis was approximately 55 ° C. The trial lasted 3 days.
- Average energy consumption: 2.988 kWh / kg of chlorine;
- Average current efficiency: 90.5%.
Les deux exemples dont la description suit diffèrent des exemples de la première série d'essais par la valeur de consigne imposée, qui a été choisie de manière qu'il y corresponde une distance anode-cathode de 1 mm dans le cas d'une anode neuve.The two examples, the description of which follows differ from the examples of the first series of tests by the imposed nominal value, which has been chosen so that there corresponds an anode-cathode distance of 1 mm in the case of an anode. new.
La cellule a fonctionné sous une densité de courant cathodique de 7,6 kA/m², durant 14 jours, la température dans la cellule étant stabilisée à 60°C.
- Consommation énergétique moyenne : 3,167 kWh/kg de chlore;
- Rendement de courant moyen : 90,2 %.The cell operated under a cathodic current density of 7.6 kA / m² for 14 days, the temperature in the cell being stabilized at 60 ° C.
- Average energy consumption: 3.167 kWh / kg of chlorine;
- Average current efficiency: 90.2%.
La cellule a fonctionné sous une densité de courant cathodique de 4,3 kA/m², durant 3 jours, la température dans la cellule étant stabilisée à 54°C.
- Consommation énergétique moyenne : 2,992 kWh/kg de chlore;
- Rendement de courant moyen : 87,9 %.The cell operated under a cathodic current density of 4.3 kA / m², for 3 days, the temperature in the cell being stabilized at 54 ° C.
- Average energy consumption: 2.992 kWh / kg of chlorine;
- Average current efficiency: 87.9%.
Après avoir réglé le fonctionnement de la cellule comme dans l'essai de l'exemple 3 (densité de courant cathodique : 7,6 kA/m²; température : 60°C; valeur de consigne correspondant à une distance anode-cathode de 1 mm dans le cas d'une anode neuve), on a soumis chaque anode à un test de contrôle, comprenant les étapes successives suivantes :
- relever l'anode de 1 mm,
- mesurer l'augmentation résultante de la résistance électrique de la couche de saumure sous l'anode,
- comparer l'augmentation de résistance électrique à la valeur de seuil imposée (30 µOhm.m²/S, où S est l'aire de l'anode, exprimée en m²),
- redescendre l'anode de 1 mm, si l'augmentation de résistance électrique est égale ou inférieure à la valeur de seuil imposée.After having adjusted the operation of the cell as in the test of Example 3 (cathode current density: 7.6 kA / m²; temperature: 60 ° C; setpoint corresponding to an anode-cathode distance of 1 mm in the case of a new anode), each anode was subjected to a control test, comprising the following successive steps:
- raise the anode by 1 mm,
- measure the resulting increase in the electrical resistance of the brine layer under the anode,
- compare the increase in electrical resistance to the imposed threshold value (30 µOhm.m² / S, where S is the area of the anode, expressed in m²),
- lower the anode by 1 mm, if the increase in electrical resistance is equal to or less than the imposed threshold value.
Le test de contrôle a révélé 19 anodes pour lesquelles l'augmentation de la résistance a été supérieure à la valeur de seuil. La cellule a dès lors fonctionné avec 19 anodes occupant une position correspondant à une distance anode-cathode théorique de 2 mm (anodes corrigées) et 161 anodes occupant une position correspondant à une distance anode-cathode théorique de 1 mm (anodes maintenues dans la position de référence). L'essai a duré 45 jours et a donné lieu aux résultats suivants :
- consommation énergétique moyenne : 3,090 kWh/kg de chlore;
- rendement de courant moyen : 92,5 %.The control test revealed 19 anodes for which the increase in resistance was greater than the threshold value. The cell therefore operated with 19 anodes occupying a position corresponding to a theoretical anode-cathode distance of 2 mm (corrected anodes) and 161 anodes occupying a position corresponding to a theoretical anode-cathode distance of 1 mm (anodes maintained in the position reference). The trial lasted 45 days and resulted in the following results:
- average energy consumption: 3,090 kWh / kg of chlorine;
- average current efficiency: 92.5%.
On a répété l'essai de l'exemple 5, dans les conditions d'électrolyse de l'exemple 4 (densité de courant : 4,3 kA/m²; température : 53°C; valeur de consigne correspondant à une distance anode-cathode de 1 mm dans le cas d'une anode neuve). Les résultats suivants ont été obtenus :
- consommation énergétique moyenne : 2,945 kWh/kg de chlore;
- rendement de courant moyen : 89,5The test of Example 5 was repeated, under the electrolysis conditions of Example 4 (current density: 4.3 kA / m²; temperature: 53 ° C; setpoint corresponding to an anode distance- 1 mm cathode in the case of a new anode). The following results were obtained:
- average energy consumption: 2.945 kWh / kg of chlorine;
- average current efficiency: 89.5
On a réalisé un essai analogue à celui de l'exemple 5, dans les conditions suivantes :
- densité de courant cathodique : 7,6 kA/m²;
- valeur de consigne correspondant à une distance anode-cathode théorique de 0,7 mm, dans le cas d'une anode neuve.A test similar to that of Example 5 was carried out under the following conditions:
- cathodic current density: 7.6 kA / m²;
- setpoint corresponding to a theoretical anode-cathode distance of 0.7 mm, in the case of a new anode.
Le test de contrôle a révélé 28 anodes pour lesquelles l'augmentation de la résistance électrique a été supérieure à la valeur de seuil. Ces 28 anodes ont dès lors été relevées de 1 mm par rapport à la position de référence initiale.The control test revealed 28 anodes for which the increase in electrical resistance was greater than the threshold value. These 28 anodes were therefore raised by 1 mm from the initial reference position.
L'essai a duré cinq jours et a donné lieu aux résultats suivants :
- consommation énergétique moyenne : 3,034 kWh/kg de chlore;
- rendement de courant moyen : 91,2 %.The test lasted five days and resulted in the following results:
- average energy consumption: 3,034 kWh / kg of chlorine;
- average current efficiency: 91.2%.
On a répété l'essai de l'exemple 7 avec une densité de courant cathodique de 4,3 kA/m².The test of Example 7 was repeated with a cathode current density of 4.3 kA / m².
Les résultats suivants ont été obtenus :
- consommation énergétique moyenne : 2,944 kWh/kg de chlore;
- rendement de courant moyen : 89,2 %.The following results were obtained:
- average energy consumption: 2.944 kWh / kg of chlorine;
- average current efficiency: 89.2%.
Les résultats des essais sont consignés aux tableaux suivants. Le tableau I concerne les essais d'électrolyse sous une densité de courant de 7,6 kA/m² (exemples 1, 3, 5, 7), et le tableau II concerne les essais d'électrolyse sous une densité de courant de 4,3 kA/m² (exemples 2, 4, 6, 8).
Les résultats des essais montrent que le procédé selon l'invention (exemples 5 à 8) réalise un bilan énergétique optimum grâce à l'obtention d'un meilleur compromis dans la recherche d'une faible tension d'électrolyse et d'un haut rendement de courant.The results of the tests show that the process according to the invention (examples 5 to 8) achieves an optimum energy balance thanks to the obtaining of a better compromise in the search for a low electrolysis voltage and a high efficiency. current.
Claims (8)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT90201008T ATE93550T1 (en) | 1989-05-03 | 1990-04-23 | PROCEDURE FOR ADJUSTING AN ANODE SET IN A MERCURY CATHODE ELECTROLYTIC CELL WHICH PRODUCES CHLORINE. |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT2036289 | 1989-05-03 | ||
| IT8920362A IT1229328B (en) | 1989-05-03 | 1989-05-03 | PROCEDURE FOR POSITIONING AN ANODIC UNIT IN AN ELECTROLYTIC CELL WITH A MERCURY CATHOD, IN WHICH CHLORINE IS PRODUCED. |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0396174A1 true EP0396174A1 (en) | 1990-11-07 |
| EP0396174B1 EP0396174B1 (en) | 1993-08-25 |
Family
ID=11166056
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP90201008A Expired - Lifetime EP0396174B1 (en) | 1989-05-03 | 1990-04-23 | Process for positioning an anode set in a mercury cathode electrolysis cell wherein chlorine is produced |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0396174B1 (en) |
| AT (1) | ATE93550T1 (en) |
| BR (1) | BR9002048A (en) |
| DE (1) | DE69002857T2 (en) |
| ES (1) | ES2045757T3 (en) |
| IT (1) | IT1229328B (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4004989A (en) * | 1974-04-18 | 1977-01-25 | Olin Corporation | Method for automatic adjustment of anodes based upon current density and current |
| FR2491958A1 (en) * | 1980-10-13 | 1982-04-16 | Costes Jean | Adjustment of anode:cathode distance - in electrolysis cells using mercury cathode, so substantial savings in electricity consumption can be achieved |
-
1989
- 1989-05-03 IT IT8920362A patent/IT1229328B/en active
-
1990
- 1990-04-23 DE DE90201008T patent/DE69002857T2/en not_active Expired - Fee Related
- 1990-04-23 AT AT90201008T patent/ATE93550T1/en not_active IP Right Cessation
- 1990-04-23 EP EP90201008A patent/EP0396174B1/en not_active Expired - Lifetime
- 1990-04-23 ES ES90201008T patent/ES2045757T3/en not_active Expired - Lifetime
- 1990-05-02 BR BR909002048A patent/BR9002048A/en not_active IP Right Cessation
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4004989A (en) * | 1974-04-18 | 1977-01-25 | Olin Corporation | Method for automatic adjustment of anodes based upon current density and current |
| FR2491958A1 (en) * | 1980-10-13 | 1982-04-16 | Costes Jean | Adjustment of anode:cathode distance - in electrolysis cells using mercury cathode, so substantial savings in electricity consumption can be achieved |
Also Published As
| Publication number | Publication date |
|---|---|
| BR9002048A (en) | 1991-08-13 |
| IT1229328B (en) | 1991-08-08 |
| ES2045757T3 (en) | 1994-01-16 |
| IT8920362A0 (en) | 1989-05-03 |
| DE69002857T2 (en) | 1994-03-17 |
| DE69002857D1 (en) | 1993-09-30 |
| ATE93550T1 (en) | 1993-09-15 |
| EP0396174B1 (en) | 1993-08-25 |
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