Technical Field

The present invention relates to a method and a device for monitoring individual anode currents in electrolytic cells for production of aluminium which cells are equipped with prebaked carbon anodes.

Background Art

Electrolytic aluminium production cells equipped with prebaked anodes can be divided into two types:

1. Cells having fixed bridge.

2. Cells having pair-controlled anodes.

In electrolytic cells having fixed bridge the prebaked anodes are locked to a fixed bridge arranged above the electrolytic cell and electric current is supplied to the anodes through current-conducting flexibles connecting the ends of the fixed bridge with the busbars.

In electrolytic cells having pair-controlled anodes, each pair of anodes is connected to the bridge by means of current-conducting flexibles and each pair of anodes can be adjusted relative to the bridge. The bridge itself is fixed to the busbars.

For electrolytic cells having fixed bridge, the anode current is monitored by manual measurement of the voltage drop for a fixed length of each anode bolt 1 - 2 times each shift by means of two spikes which are forced against the anode bolt. The measurement is filtered with a time factor of at least 2 seconds in order to obtain a mean value. These manual measurements are very time consuming. Thus for electrolytic cells having 18 anodes it is needed 4 - 6 man-hours for a serie of 200 electrolytic cells in order to obtain reliable measurements. Due to the low frequency of measurements of anode current, a number of anodes which may take a too high current over a long time, will be lost.

For pair-controlled furnaces the current distribution is automatically measured 2 - 4 times a minute. These measurements are registered by a computer which also regulate the anodes. By these mesurements it is the average current in each pair of anodes that

is measured and thus an uneven current distribution which may give rise to an overload for one of the anodes in the pair, cannot be detected. The current is typically measured using a filtering constant of 2 seconds.

For both types of cells, it is thus not possible using the present current mesurement methods to get an overview of short time current fluctuations in the anodes and thus it is not possible to obtain a view of the dynamic state of the cells. Thus cell operation disturbances such as pointed anodes, coal pieces moving about in the electrolyte below the anodes, wave movements in the metal, magnetic disturbances from neighbouring cells which are out of operation, will only be detected as very small variations in the total cell resistancy, but cannot be detected for each individual anode.

Disclosure of Invention

By the present invention it is provided a method and a device for individual monitoring of anode currents in electrolytic cells for production of aluminium whereby the disadvantages of the prior art can be overcome.

Thus, according to a first aspect, the present invention relates to a method for individual monitoring of anode current in electrolytic cells for production of aluminium which cells are equipped with prebaked anodes, wherein the current for each anode is measured continuously and the current is shown in an display whereby the current for each anode can be red continuously.

The current measurements are preferably shown on a display formed as a picture of the electrolytic cell, which display contains a column for each anode where each column contains a plurality of rows, where each row is intended to represent a preselected current strength.

The rows in each column preferably contains light emitting diodes.

According to another aspect, the present invention relates to a device for displaying individual anode current in electrolytic cells for production of aluminium which cells are equipped with prebaked anodes, which device comprises a display containing one column for each anode in a cell, where each column consists of a plurality of rows each row representing a preselected current strength.

The rows in each column is preferably made up from light emitting diodes.

Each column may for instance contain 10 light-emitting diodes where each diode represents 2KA. The column for each anode can thus display a current strength in the interval of 0 to 20 KA.

By the method according to the present invention, one can by looking at the display, get on instantaneous view of the current distribution between the anodes in an electrolytic cell, and in addition n^ can see how the current distribution varies with time between the individual anode-.. This can for example be used to locate waves in the metal or carbon pieces floating about in the cell, as these phenomenons can be observed as short-time current in tses which moves between the anodes and thereby also moves between the coluu.-.s in the display.

The display can in principle be located anywhere, but it is preferred to arrange the display near each cell.

In order to control the current distribution in a serie of 200 cells it is needed only about 10 minutes, while the time for one measurement of anode current for each anode in such a serie of cells, n JS 4 - 6 man hours.

In addition to the above mentioned advantages, the present invention gives an excellent visual view of the condition of each cell, thereby making it more easy for the operators to run each cell optimally.

Brief Description of D- ..wings

Figure 1 shows schematically an electrolytic cell for production of aluminium seen from above,

Figure 2 shows an example of a display for monitoring the anode currents in the anodes shown in the electrolytic cell of figure 1.

Detailed Description of Preferred Embodiments

In figure 1 it is schematically shown an electrolytic cell for production of aluminium seen from above. The cell is equipped with 18 prebaked anodes, numbered from 1 to 18. In figure 1 the arrangement for current supply is for simplicity not shown.

On each of the anode bolts there is arranged conventional current mesurement devices (not shown). The current measurement in itself is conventional and is not a part of the present invention.

The signals from the measurements of the anode currents are transferred to a display as shown in figure 2. The display shown in figure 2 consist of 18 columns each comprising 10 rows of light-emitting diodes. The columns in figure 2 are numbered in the same way as the anodes in figure 1. The anode current for anode 1 in figure 1 is thus connected to column 1 on the display in figure 2 and correspondingly for the other 17 anodes.

Figure 2 thus gives a graphical picture of the electrolytic aluminium production cell shown in figure 1. Each of the rows of light-emitting diodes in columns 1 - 18 in figure 2 represents a current strength of 2 KA, and each column thus represent a range of current strength from 0 to 20 KA. By increase of the current strength in one anode, the light-emitting diodes are turned on from the bottom of the column and upwards as the current strength increases from 0 and upwards.

As the current measurements are not filtered, but show real time values, one will by observing the display in figure 2, get an immediate view of the current distribution for each anode for a cell. It is also possible to observe very rapid current fluctuations if such exist for one or more of the anodes. On the basis of such observations the operators can, if necessary, make the necessary change in order to restore good cell operation.

From figure 2 it can be seen that anode 6 does not carry any current at all. This is typical for a newly installed anode. Further it can be seen that anode 15 has a higher current density than the average current density for the anodes.