GB602876A - Electrolysis cell installation arranged for automatic adjustment of the position of the electrodes - Google Patents

Abstract

602,876. Automatic control systems for electrolytic apparatus. COMPAGNIE DE PRODUITS CHIMIQUES ET ELECTROMETALLURGIQUES ALAIS, FROGES, ET CAMARGUE. April 9, 1945, No. 8764. Convention date, April 7, 1944. [Class 38 (iv)] In an electrolysis cell the electrode positions are controlled by relays measuring the cell resistance and electrode current distribution. In Fig. 1, A.C. motors 1, 2 drive racks with associated electrodes and are normally connected to bus-bars 15, 16 by contactors 11, 12, 13, 14 to allow upward or downward movement of the electrode. Upon an alteration in the overall cell resistance, the left- or right-hand contact of relay 8 close, according as the resistance is below or above a datum level to operate contactors 9 or 10 which connect lines 16 or 15 to the appropriate supply phases. The contactors 9, 10 may alternatively be operated by push-buttons (not shown). The relays 17, 18, &c. control the relation between the electrode currents with respect to the total cell current. If an electrode position, and hence the current carried by the electrode deviates from a set valve, the right- or left-hand contacts of the associated relay 17, 18, &c. close, if,the electrode is too high or low, respectively. The corresponding reversing contactor 19, 20, 21 or 22 is energized, thus opening the normally closed contactors 11, 12 or 13, 14, and simultaneously closing contactors 23 or 24, 25 or 26, to correctively energize the motor controlling the deviating electrode from bus-bar 27. Such individual electrode corrections are received only when the cell resistance has the allotted value and the contactors 9, 10 are at rest, i.e. the bus-bars 15, 16 are not energized. If the overall cell resistance, as indicated by relay 8, is at a value other than the datum, then only those individual electrode corrections are applied which will reduce this error. Similarly, a general correction signal, consequent upon the state of relay 8, is only applied to those electrodes at or beyond the datum position. Normally closed relays 28, 29, which detect electrode current variations caused by transitory polarization of the electrodes, have measuring coils traversed by a current proportional to that through the respective electrode. Polarization of an electrode causes opening of the associated relay, and consequent interruption of the automatic control system and operation of the warning device 32. Relay 6 interrupts the supply to the automatic circuit on failure of the main cell current. Hunting is eliminated by relay 7 which periodically interrupts the electrode driving means. Automatic regulation may be suppressed, e.g. after insertion of a fresh electrode, by switches 33, 34 and each electrode may be operated by push-buttons, not shown. The system may be adapted for use with D.C. or compressed out motors. In a second embodiment, not shown, the electrodes are given a vertical oscillation to produce a progressive descent of alumina which, in powdered form, rests on the crust of solidified cryolite covering the molten bath. A change of cell resistance causes the corrective suppression of either the upward or downward movement of all the electrodes while electrode current distribution may be corrected in a manner similar to that employed in Fig. 1. In a modification in which the cell resistances measuring relay controls a given electrode, Fig. 3, the resistance measuring relay 71 moves pilot electrode 74, by means of motor 1 and rack 79, to an immersion depth which is a function of the desired cell resistance. Distribution relays 72, 73, &c. act on their respective electrodes to match the currents therein with that of the pilot electrode 74. One of the two windings of relays 72, 73, &c. is connected to electrode 74, and the other to the associated electrode through shunts. If the cell resistance rises, relay 71 closes and operates contactor 80 to energize motor 1 which moves rack 79 downwards. The consequent unbalance between the currents in electrodes 75, 76, &c. and pilot electrode 74 effects the closure of relays 72, 73 which operate contactors 80 and so move electrodes 75, 76 downwards by motors 2, 3. In all the embodiments, the electrode current distribution may be adjusted to give any distribution of the electrolysis action in the bath.