RU2166011C1 - Method of control over aluminum electrolyzer - Google Patents

Abstract

FIELD: non- ferrous metallurgy, production of aluminum by electrolysis of molten salts. SUBSTANCE: in correspondence with proposed method resistance of electrolyzer between anode and cathode buses of sectionalized current lead across one of face sections of electrolyzer is measured. At same time difference of resistance of cathode buses of center and opposite butt of electrolyzer relative to cathode bus is measured. Maximum difference of resistance between cathode buses is subtracted from resistance of electrolyzer, anode is moved over resistance of electrolyzer over section with least value of resistance. EFFECT: enhanced technical and economic indices of operation of electrolyzer. 1 cl, 1 dwg, 1 tbl

Description

 The invention relates to the metallurgy of aluminum, in particular to a method for producing aluminum by electrolysis of molten salts.

 One of the main problems of aluminum electrolysis is the stability of maintaining the interpolar distance (MPR), which provides a stable technological course of the electrolyzer and the greatest metal current output. The instability of the cathode metal and the change in the skew of its surface create an uneven value of the MPR in the longitudinal direction of the cell and uneven resistance of the cell in these areas. To increase the metal current output when adjusting the electrolyzer for resistance, it is necessary to take into account the change in the skew of the metal surface and the magnitude of the MPR in the longitudinal direction of the electrolyzer.

 Known methods of regulating the electrolyzer for ed.St. N 150230 and Aut. St. N 193732, by which the resistance of the cell is automatically measured between the anode and cathode buses, the measured resistance of the cell is compared with its predetermined value and the mismatch is eliminated by the corresponding movement of the anode.

 The disadvantage of these methods is the measurement of the resistance of the cell between the individual tires of the anode and cathode bus, which does not take into account the change in the magnitude of the MPR and the resistance of the cell in its individual sections in the longitudinal direction of the cell.

 Known methods of regulation for auth. N 177627 using a probe located in the liquid phase of the anode, and according to ed. N 960317, cl. C 25 C 3/20 1982, using the anode casing as a potential electrode.

 These methods include reducing the influence of the permutation of the pins and increasing the resistance in the anode on the stability of maintaining the MPR.

 These methods also do not take into account the change in the magnitude of the MPR and the resistance of the electrolyzer in separate sections in its longitudinal direction. Potential electrodes have an unstable potential relative to current-carrying sections and introduce an additional error in the change in the resistance of the electrolyzer when regulating the MPR.

 In order to take into account the distortion of the metal surface, methods for regulating the electrolyzer according to auth. N 1216254, cl. C 25 C 3/20 1986 using for measuring the resistance of the electrolyzer of the Central parts of the end sides of the anode and cathode casings. By auto N 1513842, class C 25 C 3/20 1989 using probes at the ends of the anode installed prior to contact with the sintering cone and probes at the ends of the cathode, with measuring the resistance at the end sections and eliminating the mismatch by appropriate movement of the anode to align the MPR in the longitudinal direction of the cell.

 The disadvantage of these methods, with all their advantages, is the use of potential electrodes with their inherent disadvantages and the distribution of the potential difference in the anode to align the MPR.

 The alignment of the MPR requires significant displacements of the anode by one of the ends. A subsequent change in the skew of the metal surface requires the movement of the anode with the opposite end. The dynamics of changes in the skewness of the metal surface causes frequent movement of the anode by the ends, the operation of the electrolyzer with skewing of the anode, increasing the unevenness of the current supply to the metal, increases the instability of the metal, which reduces the accuracy of maintaining the MPR.

 The closest in technical essence and the achieved effect to the proposed one is a method of regulation by ed. N 1435666, CL C 25 C 3/20 1988. The method is based on the simultaneous measurement of the resistance of the electrolyzer between the anode casing and each of the cathode buses, the allocation of the lowest value of the measured resistance, which support MPR.

 The disadvantage of this method of regulation is the use of the anode casing as a potential electrode with an unstable potential relative to the body of the anode. With a two-horizontal arrangement of pins in the anode, the anode casing contacting the anode at a distance of 30-40 cm from its sole made it possible to reduce the influence of the increase in resistance in the anode on the total change in the resistance of the electrolyzer and increase the accuracy of maintaining the MPR during the main technological operation of the permutation of the pins.

 The anode casing contacts the sintering cone of the anode along its perimeter. The potential of one of the sections of the perimeter of the sintering cone is transmitted to the anode casing. Depending on the potential of the section of the sintering cone in contact with the anode casing, the potential of the anode casing changes regardless of the change in the MPR. This reduces the accuracy of maintaining the MPR for a period of 50-60% of the time from the period between the permutations of the pins. With a twelve-horizontal pin arrangement, which factories are currently switching to, the voltage drop across the anode when the pins are rearranged is reduced by 6-7 times, which sharply reduces the positive effect of the anode casing on the accuracy of maintaining the MPR.

 The disadvantages of this method also include the impossibility of its use on electrolyzers with baked anodes and support MPR taking into account changes in the skew of the metal surface on these electrolyzers.

 The objective of the invention according to the proposed method is to increase the technical and economic indicators of the electrolyzer.

 The technical result of the invention is to reduce the consumption of electricity, fluoride salts, extinguishing pole to eliminate anode effects, reduce labor costs, increase the productivity of the cell by 1-2%.

 The technical result is achieved by the fact that in a method for regulating an electrolyzer with a two-sided current supply, which includes automatic measurement of the resistance of the electrolyzer between the anode and cathode nodes, comparing the obtained value with a given value of the resistance of the electrolyzer and eliminating the mismatch with the corresponding movement of the anode, the resistance of the electrolyzer is measured between the anode and cathode buses of the partitioned current supply at one of the end sections of the electrolyzer, simultaneously relatively cathodically Bus difference measured resistances cathode busbar middle and opposite end of the cell, the anode is performed by moving the cell resistance less therefrom the difference between the resistances of the tires with the cathode resistances sign of the difference. From the resistance of the electrolyzer, the largest difference of the resistances between the cathode buses is subtracted, and the anode is moved by the resistance of the electrolyzer in the area with a smaller MPR value.

 The known method of regulation does not take into account the distribution of resistances in the anode assembly, depending on the two-sided current supply and dividing the electric circuit of the cell with a zero point into sections with different resistance and uneven MPR in the longitudinal direction of the cell. This introduces an error in the measurement of the resistance of the cell relative to the anode assembly. As a result, the resistance measured by the electrolyzer does not fully take into account the non-uniformity of the MPR value and does not achieve the required accuracy of its maintenance.

 The proposed method involves improving the accuracy of measuring the resistance of the cell, depending on the skew of the metal surface. In this case, the non-uniformity of the MPR in the longitudinal direction of the electrolyzer is controlled, which provides an increase in the accuracy of maintaining the MPR when moving the anode.

 Two-sided current supply and sectioned current drainage create current-carrying sections on the electrolyzer separated by a zero point of current supply, certain buses of the sectioned anode and cathode busbars characterizing the resistance of these sections and the MPR value in these sections.

 The measurement of the resistance of the electrolyzer between the anode and cathode buses of the partitioned current supply at one of the end sections of the electrolyzer determines the magnitude of the MPR on this end section of the electrolyzer.

 Simultaneous measurement relative to the cathode bus of the difference in the resistances of the cathode buses of the middle and the opposite end of the cell determines the non-uniformity of the MPR value in the longitudinal direction of the cell relative to the section on which the resistance of the cell is measured.

 The movement of the anode along the resistance of the cell minus the resistance difference between the cathode buses, taking into account the sign of the difference in resistance, provides control of the decrease (increase) in the MPR in the section along which the electrolyzer is regulated, in relation to the increase (decrease) in the MPR in other sections separated by a zero current supply under conditions of a change in the skew of the metal surface. This allows you to move the anode, taking into account the redistribution of the MPR value in the longitudinal direction of the electrolyzer, to eliminate the “preload” or “decompression” of the MPR, thereby increasing the accuracy of maintaining the MPR in accordance with the technological state of the electrolyzer, to reduce metal losses and increase productivity.

 Subtraction from the resistance of the electrolyser of the largest difference in resistance between the cathode buses eliminates the "preload" MPR in other parts of the cell.

 The movement of the anode in the resistance of the electrolyzer in the area with a lower MPR value eliminates the most harmful technological deviation “preloading” the MPR in this region, at which the metal production is reduced to a greater extent, and metal losses due to oxidation increase.

 This method was tested at the Bratsk aluminum plant, showed good results in improving the accuracy of maintaining the MPR, stability and performance of the cell.

 Comparative analysis with the prototype shows that the proposed method is distinguished by the features claimed in the characterizing part of the claims. Therefore, this invention meets the criteria of the invention of "novelty."

 Comparison of the claimed method not only with the prototype, but also with other technical solutions in this field did not reveal similar features with the distinctive features of this proposal.

 Thus, the claimed solution meets the criteria of "inventive step" and "industrial applicability".

An example of the method
The drawing shows a schematic diagram of a partitioned busbar electrolyzer with two-sided current supply.

Одновременно измеряли разность сопротивлений между катодными шинами 2 и 4 (R_2-4) и 2 и 6 (R_2-6) также путем измерения падения напряжения между указанными шинами U_2-4 и U_2-6. Из сопротивления электролизера R_эл-ра вычитали наибольшую разность сопротивлений между катодными шинами R_2-4, R_2-6 и расcчитывали сопротивление электролизера R_рег., по величине которого регулировали МПР посредством расчета приведенного напряжения

,
где I_н - номинальный ток серии;
I_с - текущий ток серии;
E - электрохимическая составляющая сопротивления,
при отношении к текущему току серии
R_рег.=U_пр./I_с
Измерение сопротивлений и расчет R_рег. при изменении перекоса поверхности металла производили с помощью шкафов управления ШУЭБМ каждую секунду на группе из трех электролизеров. Усредненные за каждые пять минут значения сопротивления электролизера R_рег., по величину которого регулируется МПР предлагаемым и известным способами, приведены в таблице на основании расчета приведенного напряжения U_пр.The resistance of the electrolysis cell R el-ra was measured between the anode 1 and cathode 2 buses by measuring the voltage drop U el-el between these buses at a current series I _s current

At the same time, the resistance difference between the cathode buses 2 and 4 (R _2-4 ) and 2 and 6 (R _2-6 ) was also measured by measuring the voltage drop between the indicated buses U _2-4 and U _2-6 . From the resistance of the electrolytic cell R _{el, the} largest difference in the resistance between the cathode buses R _2-4 , R _{2-6 was} subtracted and the resistance of the electrolytic cell R _{reg was} calculated _. , the magnitude of which was regulated by the MPR by calculating the reduced voltage

,
where I _n is the rated current of the series;
I _s - current series current;
E is the electrochemical component of the resistance,
in relation to the current series
R _reg. = U _ave./ I _s
Resistance measurement and calculation of R _reg. when the surface distortion of the metal was changed, they were made using the ShUEBM control cabinets every second on a group of three electrolyzers. Averaged over every five minutes values of the resistance of the cell R _reg. , the magnitude of which is regulated by the MPR by the proposed and known methods, are given in the table based on the calculation of the reduced voltage U _av

 As can be seen from the table, when regulating the electrolyzer of the proposed method, the accuracy of maintaining the MPR is increased due to a smaller change in resistance, the magnitude of which the cell is regulated.

 The tests were carried out for two months. The frequency of anode effects decreased by 0.5 anode effects per day, the average cell voltage decreased by 40-50 mV, and the labor costs for maintaining the cell and monitoring the normal process flow decreased by 10%.

 The metal production allows predicting an increase in productivity by 1-2%.

 The proposed method can be used on electrolyzers with baked anodes.

Claims (2)

 1. The method of controlling an aluminum electrolyzer, including a sectioned current supply, automatic measurement of the resistance of the electrolyzer between the anode and cathode nodes, comparing the obtained value with a given value of the resistance of the electrolyzer and eliminating the mismatch with the corresponding movement of the anode, characterized in that the resistance of the electrolyzer is measured between the anode and cathode buses of the sectioned current supply at one of the end sections of the cell, simultaneously relative to the cathode bus the difference in the resistances of the cathode buses of the middle and opposite ends of the electrolyzer, the movement of the anode is carried out according to the resistance of the cell minus the resistance difference between the cathode buses, taking into account the sign of the resistance difference.  2. The method according to claim 1, characterized in that the greatest difference in the resistance between the cathode buses is subtracted from the resistance of the electrolyzer and the movement of the anode is carried out by the resistance of the electrolyzer in the area with a lower MPR value.

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