RU1790634C - Method of controlling current of series of aluminium cells - Google Patents

Abstract

The invention relates to non-ferrous metallurgy, in particular to the regulation of current on a series of aluminum electrolysis cells. The purpose of the invention is to increase current efficiency and bath life. This goal is achieved by determining the magnitude of the base current (le) depending on the average amount, voltage and duration of the anode effects, and the voltage on the series additionally. The invention relates to the electrolytic production of metals and can be used to control the current of a series of aluminum electrolytic cells . A known method of controlling the series current is to change it by means of technological influences on electrolyzers under conditions of constant voltage supported by a converter substation. The known method has not found application because of the difficulty of obtaining average current values within the limits necessary to maintain normal values, they change from condition I (t) b, moreover, cf. The method is carried out as follows: based on the technology values of Cp, counter-EMF, the average voltage on the bathtubs with anode effects, the operating voltage of the bathtubs, the frequency and duration of the anode effects for a series of baths, the value of the base current is determined and corrected from this value up to a value equal to the rated (average) current of the series (with a prolonged absence of anode effects), the average current of the series is maintained. If technological influences on the series on average do not satisfy the requirements of the technological regulations, then the current on the series is not maintained, because its maximum value is limited by the calculated value of the base current. When the technology is established (monotonously) within the time limits, the series current curve is a view in the form of a basic current level, from which periodic series current decreases occur due to the anode effects that appear on the bathtubs. technological (thermal) mode of electrolyzers. There is also a known method of controlling the series current by its instantaneous value using saturation chokes and controlled valves. A prototype of the proposed control method is a method for controlling the series current, including changing the voltage supplied to the series of electrolyzers when the current l (t) of the series deviates from the average average value of Cp set by the technology. In this method, the current is regulated by eating С 4 О О О СО 4 СО

Description

its average value, when the voltage supplied to the series is changed in such a way as to withstand the transmitted hours (set average current) for the set time intervals (1-2 hours), regardless of whether the technology is being carried out in accordance with the established technological schedule or no. As is known, the main factors that determine the magnitude of the series current are the frequency, magnitude of the voltage and duration of the anode effects.

For example, if the technological regulations for a series of electrolytic cells set the values of counter-EMF, 4V, operating voltage of one electrolytic cell, 2V, voltage on the electrolytic cell with an anode effect (, 2V) on it, the frequency of the anode effects f and the damping time of one anode effect t, then according to the prototype (p. 31, the formula for the h - current of the series in the absence of anode effects on it) in order to maintain the average current 1Ср 150 kA, it is necessary to maintain the current And on the series in the absence of anode effects: - 154.9 KAnpnf 2,, t 2 ,5 minutes.; - - the value of 160.8 kA (in the prototype text 160.5 kA due to the lower accuracy of the calculation) at, min. and a value of 172.8 kA at,, 5 min, D.

T.O. when regulating the current according to the prototype, the value of the maximum series current is not attached to the value and theoretically it can be anything, because the main thing (given by technology) is (considered) to withstand the average current (transferred ampere hours) for the established time intervals of 1-2 hours.

It is believed that the smaller the average current values differ from the set value, the better the optimal working state of the electrolytic cells in terms of heat balance is ensured, which would positively affect the current output, as well as increase the service life of the electrolytic cells.

As a result of the described current control according to the prototype, the current curve in the diagram has a wave-like character with large current values necessary to withstand the average current at set intervals.

Vibrational modes with reaching the maximum current value can be very long and the average current is usually maintained, the thermal balance of the cells is observed. The disadvantage of the prototype is the assumption of the operating mode of the series with large maximum current values, which leads to increased circulation of the melt in the electrolytic cells, to accelerate the erosion of the lining for this reason, and reduce its life

service, to increased consumption, loss of raw materials (anodes, alumina, cryolite, etc.), to an increase in the specific consumption of electricity, to a decrease in the metal current output.

The purpose of the invention is to increase the current efficiency and the service life of electrolyzers (as well as other indicators, such as unit consumption of raw materials and electricity).

The goal is achieved in that

additionally determine the value of the base current of series b depending on the average amount, the voltage and duration of the anode effects on the electrolyzers of the series, the voltage on the series is additionally changed from condition l (t) b, and the base current can also determine mathematical expression

 I

wed

NT t f

(M-1) + tgCh

 + (24-N-ff)

IE

where the values specified by the technology enter:

24 1Ср - daily ampere hours;

N is the number of cells in the series;

f is the number (frequency) of anode effects on one electrolyzer per day;

t is the duration in time of one anode effect;

Iae is the average voltage on the cell in the presence of the anode effect on it;

IE — voltage on the cell in the absence of an anode effect on it;

e-counter EMF of the electrolyzer.

The proposed method is as follows:

1. For electrolysis series:

- consisting of N series-connected electrolysers; - with an average counter-emf of each cell - e;

- with an average operating voltage on each cell (without taking into account the anode effects) - IE;

- with an average frequency of anode effects on each cell per day - f;

- with an average duration of one anode effect on the cell - t;

- with an average value of voltage on the cell during the anode effect

 14ae1

The listed characteristics (parameters) are set by the technological regulations and based on them the base current is calculated according to the following formula 1.1. 241SR

b

  t f

Us

(N 1) + -Ј

- + (24 - N t f)

Js -e

which is derived from the following. 1.1.1

. Ud -e N 16

i) +

 Us i

Rb N

where Rb is the resistance of one cell in the absence of an anode effect on it; Ud is the voltage of the series. 1.1.2. A formula for determining the series current when one anode effect arises on it (on one of the bathtubs). -e N

 1ae ---------

Rb (N.,... „Уе - е

1.1.3. Relationship is found

l (

1aen

1.1.4. The total duration of anode effects per day is determined

1ae t f

1.1.5. The number of ampere hours transmitted per day is determined as

1.1.5.1 Icp X 24, where 24 is the number of hours per day

1.1.5.2. 1AeM t f + le (24-N t f)

1.1.6, Icp 24 ia3N t f + le (24-N t f)

Substituting the ae value from the formula 1.1.3 into this formula, we obtain the formula 1.1 for the base current.

1.2. When substituting the mean values of the parameters into formula 1.1, we obtain the maximum base current

1.3. When substituting in the formula 1.1 the values of f 0 t 0 (with a long absence of anode effects) we obtain the minimum value of the base current I e min Icp.

2. The basic value of the current is corrected (adjusted, changed) within its values equal to the specified nominal (average) current of the series to its maximum value determined from the requirements of the technological regulations and this adjustment of the basic current is carried out in order to maintain the specified average current for long periods of time.

5

0

fifteen

P

5

about

5

0

5

0

5

3. The time intervals over which the average current must be maintained (1-2 hours, for example, in the prototype) are not set. The average current is maintained if the process is carried out within the requirements of the technological regulations and is not maintained otherwise. Exceeding the maximum base current is prohibited.

The average current is maintained as a result of adjusting the base current depending on the actual progress of the technology within the time limit and as a result of maintaining the technology itself according to the requirements of the process time limit.

4. Maintaining the base current at the required level is carried out by means of voltage regulation on the electrolysis series, for example, switching devices, by which the number of turns of the primary (network) windings of converter transformers is stepwise changed.

To be able to estimate the instantaneous values of the series current and, therefore, the base current, i.e. series current values during the period of operation of the series without anode effects, special electronic devices with digital indication for measuring series current are used. During periods of anode effects, the potential level of the base current is provided, for example, by maintaining the steps on the transformer transformers that were in the previous non-flash period with a change in these steps, taking into account the predicted change in the total resistance of the series electrolytic circuit (in the absence of anode effects on it) and taking into account changes in the mains voltage (i.e. voltage supplied to the converter substation from the power system) - i.e. compensates for changes in the total resistance of the series and changes in the mains voltage. Automatic control and adjustment of the maximum current is possible. Actual levels of the base current with which the average current has withstood one or another change of the electrolyzer shop are estimated using series current chart diagrams or using special instruments measuring the base current. The base current with which the average current is maintained can serve as an operational criterion for maintaining the technology. For comparison with the prototype, we indicate that the maximum current value in the above example is, according to our formula (1.1), a value of 154.5 kA (and no more) instead of 154.9 kA, 160.8 kA and 172.8 kA according to the prototype for various technological

situations. The diagram of the series current when regulating it according to the base value has the form (with one constant value of the base current with a uniform technological process). The same result of current control (in the form of a given average value) is achieved in various ways. Moreover, if the thermal state of the electrolytic cells can be considered approximately the same root mean square, i.e. effective value of the current is less), then the magnetoelectrodynamic state of the electrolyzers will be clearly different due to different current values of the current. The higher the value of the series current, the stronger the circulation of the melt in the electrolyzer, caused by the interaction of its conductors with the current, as well as the interaction with the conductors of neighboring electrolyzers. For two current conductors, one of which in our case is a melt, the interaction force that causes circulation, the movement of the melt, is determined by the formula known from theoretical electrical engineering

g-I 2 I F g.

where iu0 is the magnetic permeability;

AND; flowing through conductors, each of which is proportional

series current;

I-length of parallel conductors with current;

g- distance between conductors.

It can be seen from the formula that the circulation intensity is proportional to the square of the series current. When regulating the current according to its basic value (and it is called basic,

because from this set level of the maximum series current, as from the base level there are periodic decreases in the series current, caused mainly by the anode effects on the electrolysis cells), the maximum current values exceed the nominal current up to 3%, and when regulating according to the average current, up to 15% or more. By adjusting to the base value, the current efficiency and the service life of the electrolysis cells significantly increase, and the specific consumption of raw materials (alumina, anodes, cryolite, etc.) and electricity are reduced. Thus, the proposed method of regulating the current series according to

its basic value allows to reduce the maximum current values, thereby reducing the circulation of the melt and increasing the current efficiency and the service life of electrolyzers, reducing unit costs

raw materials and electric energy.

Claims (2)

1. A method of controlling the current of a series of aluminum electrolytic cells, including changing the voltage supplied to the series of electrolytic cells when the current l (t) of the series deviates from the average value specified by the technology (1Cp), characterized in that, in order to increase the current efficiency and the service life of the electrolytic cells, the basic current value (1b) is additionally determined depending on the average quantity, the voltage value and the duration of the anode effects on the series electrolytic cells, and the voltage on the series is additionally changed from the condition l (t) 1b, p When in use, b. 2. The method according to claim 1, with the exception that the base current is determined by a mathematical expression b v U3 -th where 24lcp - daily ampere hours; N is the number of cells from the series; f is the number of anode effects per electrolyzer in 24 hours; t is the duration in time of one anode effect; iae — average voltage on the cell in the presence of an anode effect on it; Us is the voltage on the cell in the absence of an anode effect on it; e - counter-EMF of the electrolyzer.