JPS5943891A - Method for supplying alumina into electrolytic cell for aluminum production - Google Patents

Abstract

PURPOSE:To save labor for supplying alumina and to improve energy efficiency, by repeating following treatments such as an anode effect treatment and a moving treatment anode up and down after the treatment, to supply repeatedly alumina into an electrolytic cell for a prescribed time from a gap between crusts formed by the movement. CONSTITUTION:Al is produced by electrolysis and reduction of alumina in an electrolytic cell as follows. That is, following treatments are repeated; an effective treatment of an anode is performed and thereafter the anode is moved up and down, kept under the state for a prescribed time, returned to the original position, and the deposited alumina is supplied to the cell after forming a gap between the anode and the crusts formed at the bottom periphery of the anode. In this case, the operation for supplying the deposited alumina replenished onto the crusts from the crust gap to the cell is repeated at a cycle according to the concentration of the alumina in the cell for the prescribed time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dispensing hair alumina in an aluminum tank that saves labor and improves energy efficiency.

In general, alumina is supplied into an aluminum electrolytic cell periodically so as to cover the coagulated layer (so-called crust) of the bath formed above the electrolytic bath and below the anode and the anode layer, thereby preventing oxidation of the anode and rhff. ,,! Along with holding the alumina, the alumina is preheated and the crust is broken periodically at a rate of about 3 to 8 times a day, and the crust is fed into the tank together with the crushed crust. Alumina is supplied into the tank by crushing and simultaneously supplying alumina.

The alumina concentration in the tank is maintained within a range of 2-8M. There are various theories regarding the anode effect in aluminum electrolytic cells.

Mainly due to the change in interfacial tension associated with the decrease in the concentration of alumina in the bath, the anode gas, which normally forms bubbles and is dissipated out of the bath, spreads to the bottom surface of the anode and covers the anode surface with a gas film. .

Under normal conditions, it is operated at 4 to 5 V, and there is only a fluctuation of about 1 inch, but this is a phenomenon in which the voltage suddenly changes to 30 to 40 V, and the alumina concentration at this time is usually around 1 inch. ing. However, when the anodic effect occurs,
For example, by a mobile crust crusher driven by compressed air, or by a crust crusher provided in each electrolytic cell (for example, JP-A No. 49-38809,
If an anode effect treatment is performed in which the crust is split, alumina is supplied, and the bath is stirred, as described in Japanese Patent Laid-Open No. 55-116310, etc., the voltage returns to normal and bubbling of the anode gas resumes. Additionally, if the alumina concentration in the bath rises above the saturation concentration, alumina in the bath will deposit on the cathode surface.
So-called sludge is produced, and in an electrolytic cell that has produced sludge, the current efficiency is significantly reduced, and it takes a long time to recover to a normal state. Therefore, many methods have been proposed for automatically and continuously supplying alumina for the purpose of saving labor in supplying alumina or reducing the frequency of occurrence of the anode effect. (For example, JP-A-55-1451
(No. 88, etc.) However, if continuous supply is continued and V.
・During operations such as splitting, the temperature inside the tank increases as the temperature in the upper layer (-1) of the bath formed from the tank wall to the bottom cathode gradually recedes. However, the current efficiency decreases due to bath leakage, an increase in silicon in the aluminum produced, and an increase in the width of the aluminum layer at the bottom of the bath (-i).

This results in problems such as an increase in floating carbon and slow consumption of the anode.

The present inventors solved these problems by 1. As a result of repeated research on the method of supplying the alumina obtained, we have determined how to deal with the anodic effect when it occurs, and how to lower the anode to create a gap in the holding L crust and supply alumina into the tank through that gap. The present invention was made based on the recognition that the object can be achieved by repeating a time-repeating processing method. Namely.

The present invention relates to the production of aluminum by electrolytically reducing alumina in an aluminum electrolytic tank.

Anode effect treatment and a crust formed in the lower layer of the anode above the electrolytic bath by moving the anode upward and/or downward after the anode effect treatment and returning it to the restoring position where the anode was held upward or downward for a predetermined time. A process is repeated for a predetermined period of time according to the alumina concentration in the tank by creating a gap between the two and replenishing the crust from the gap and supplying the deposited alumina into the tank for a predetermined period of time. This is a method of supplying hair alumina in an aluminum electrolytic tank.

In the method of the present invention, in order to supply hair alumina into the electrolytic bath, a gap is formed between the crust formed on the lower circumference of the two anodes and the side surface of the anode, and the alumina on the crust is fed into the bath. However, in order to form a gap between the crust and the side surface of the anode, the anode must be pulled upward or.

By pushing down, pushing up and down, or pushing down and pulling up (hereinafter referred to as up and down movement of the anode).

However, cracks are generated in the part where the crust is adhered to the side surface of the anode, which is the thinnest part of the crust, and a gap is formed. Therefore, the anode is 19['i'+q l'l'
After moving the anode up and down J height and holding it for a predetermined time, the anode is pushed down or pulled up upwards and returned to the original anode position fY'r. 1 for 11 J of vertical movement of this anode. In each case 5 to 15 mn upwards or downwards, preferably.

17. Do this in the range of 8 to 12++1++1. The time period for which the anode is held in the -1 direction or downward direction is 3 to 12 seconds, preferably 4 to 10 seconds.

During this period, alumina automatically falls continuously in small amounts into the tank from the gap formed between the nozzle and the anode, and new last is formed in this gap and the gap is closed. Supplied.

The supply of alumina by this method, that is, the vertical movement of the anode, is carried out at intervals of 2 to 10 minutes, preferably every 4 to 8 minutes, depending on the alumina concentration in the electrolytic bath. Therefore, the alumina concentration in the bath, the amount of alumina supplied, etc. are estimated based on the method of estimation from the resistance change of the electrolytic cell, the number of times the anode effect occurs, the interval between the occurrences of the anode effect, etc.
The downward movement period should be increased or decreased as appropriate.

However, the supply of alumina by vertical movement of the anode can be carried out for a predetermined period of time depending on how often the anode effect is to be generated, for example, when the anode effect is to be generated about twice a day.
This operation is continued for 5 to 6 hours, and then stopped at the next anodic effect treatment. When the first anode effect occurs, normal anode effect processing is performed, and then the operation of lowering the anode for a predetermined period of time is repeated.

In addition, it is preferable to replenish the required amount of alumina to the electrolytic cell on the crust 5 to 6 times a day, including the amount directly supplied into the cell during the anode effect treatment, but it is preferable to replenish the required amount onto the crust 1 to 3 times a day.
There is no problem even if it is set to 8.

In the present invention, the anode can be moved up and down in various ways as described above, and the automatic falling rate and amount of alumina from the gap change depending on the way it is moved. Each of the many electrolytic cells has its own individuality, and the conditions are different for each one. Therefore, in order to manage a large number of electrolytic cells, it is necessary to make some adjustments according to the fluctuation factors of each electrolytic test, and after switching to the method of the present invention.

Measure the tank resistance every 1 to 60 seconds12. Every certain period of time, for example, every 2 to 4 hours, the anode is stopped moving downward for a certain period of time, for example, 10 to 30 minutes, and the tank resistance at that time is above a certain value.
For example, if the anode effect occurs within a target time, for example, 20 hours, the anode is restarted and the method of the present invention is carried out, and the tank resistance If the rise of the anode is above a certain value but the anode effect does not occur within the target time, stop the vertical movement of the anode and wait for the next anode effect to occur within the target time. Adjust accordingly.

In addition, when the rise in tank resistance is below a certain value, the method of the present invention is carried out by performing operations such as stopping the vertical movement of the anode until dl shows an increase above a certain value, thereby satisfying a predetermined condition. Make sure to implement it.

Alternatively, for a certain predetermined period of time after the anodic effect treatment, for example 20
After ~24 hours have passed, it is possible to stop the vertical movement of the anode and wait for the next anode effect.

In addition, when the anode effect occurs at short intervals such as the average of the past three anode effect occurrence intervals of 12 to 20 hours, or when the anode effect occurs frequently.

For example, if the anode effect in the past 3 days is 31R& or higher, change the anode vertical movement period to 2 minutes every 4 minutes.
Preferably, the method of the invention is carried out according to a predetermined target, such as every minute or by varying the holding time above or below the anode, for example from 5 seconds to 10 seconds.

The present invention involves repeating the anode effect treatment and the operation of creating a gap between the anode and the crust by moving the anode up and down, and continuously supplying alumina from that gap into the tank little by little for a predetermined period of time. As a result, the alumina concentration can be kept constant while generating an appropriate anode effect, and the heat distribution in the electrolytic cell can be kept good, preventing freeze retreat and crust thickness increase/decrease, and preventing bath leakage. It is possible to prevent an increase in silicon content in aluminum, an increase in floating carbon, and a delay in anode consumption, and it is possible to reduce crust cracking during the anode effect treatment, so it is possible to improve current efficiency while achieving a labor-saving effect of 1A1. The Inukip C effect is recognized.

Next, one embodiment of the present invention will be described.

[Example] Using a 130 KA Tago type electrolytic cell equipped with a pre-fired anode, after reaching a steady state, the anode was pulled up by 12 mm every 4 minutes while measuring the cell resistance every 30 seconds. hold for seconds,
Press down 12+um and repeat without returning to the original position for 10 hours after the previous anode effect treatment. Then, alumina was continuously supplied into the tank in small amounts through the gaps and cracks, and these treatments were repeated for 6 months.

The target number of times the anode effect occurs is twice a day, and alumina is replenished at a rate of 300 k7 per time, six times a day (including anode effect treatment).

The results obtained during this period are shown in the table below.

COMPARATIVE EXAMPLE Using an electrolytic cell similar to that of Example I, an anodic effect was generated in accordance with conventional methods, and alumina was produced.

The following table shows the results obtained during 6 months of operation in which the crust was split 6 times and 300 kq of alumina was supplied each time, including during the anode effect treatment.

Note] *mark: Crust splitting and alumina supply time ω
) ratio between the method of the present invention and the conventional method: 6/18x 100
= 33 Patent applicant Nippon Light Metal Co., Ltd.

Claims (1)

[Claims] 1) When producing aluminum by electrolytically reducing alumina in an aluminum electrolytic tank, anode effect treatment is performed, and after the anode effect treatment, the anode is moved in three directions and/or downward to move the anode upward or downward. After holding for a predetermined time, return to the original position to create a gap between the crust formed in the lower layer of the anode above the electrolytic bath and the anode, and supply the deposited alumina onto the crust from the gap into the tank. A process in which the operation is repeated for a predetermined period of time depending on the alumina concentration in the tank. A method for supplying hair alumina in an aluminum electrolytic cell, characterized in that the process is repeated.