RU2057823C1 - Aluminum electrolyzers processing parameters control method - Google Patents

Abstract

FIELD: aluminum production process automatization. SUBSTANCE: according to results of simultaneous measurements of current and voltage drop at area of anode - cathode of a. c. electrolyzer they determine acting value of current alternating component of each harmonic in a train, that is used for measurements. For this purpose they determine line of regression, that connects measured values of current harmonics of the train and caused by them voltage drop in electrolyzer. After that using system of equations complex impedance of electrolyzer is determined. Then, taking into consideration skin-effect on frequencies of measurement, value of active resistance is verified. Value of reverse electromotive force and concentration of alumina from given formulae. EFFECT: improved production process. 1 dwg

Description

 The invention relates to the field of automation of the process of production of aluminum from cryolite-alumina melts, more specifically to automatic control of the magnitude of the back EMF, active resistance, the concentration of alumina in the electrolyte and the interpolar distance.

 The listed parameters are used in the automated process control system of aluminum electrolysis or by the maintenance personnel of the electrolysis shop to assess the technological state of the electrolysis baths and generate regulatory actions.

,
где R активная cоставляющая сопротивления электролизера, измеренная на частоте кратной 50 (60) Гц;
К коэффициент, учитывающий изменение активного и индуктивного сопротивлений массивного проводника с ростом частоты.A known method and device for monitoring and control of the above parameters, including measuring the constant and variable components of the voltage drop across the cell and series current and calculating the resistance of the cell. Measurements of the constant and variable components of the voltage drop across the electrolyzer and series current are carried out simultaneously, and measurements on alternating current are performed at harmonics that are multiples of the frequency of 50 or 60 Hz, and the value of the back emf is determined by the results of the measurements by the formula
E _about = U _e -I _with R _e where I _c , U _{e the} constant components of the series current and voltage on the cell;
R _{e the} active component of the resistance of the cell equal to R

,
where R is the active component of the resistance of the cell, measured at a frequency multiple of 50 (60) Hz;
K coefficient taking into account the change in the active and inductive resistances of a massive conductor with increasing frequency.

 The disadvantage of this method is the significant error and instability of the data due to errors in determining the variable component of the series current at frequencies that are multiples of 50 Hz.

 The objective of the invention is to improve the accuracy of control of resistance, back EMF, alumina concentration in the electrolyte and the pole gap (anode-cathode distance) of the aluminum electrolyzer.

I_i;
r₁= (1/N)

I_iU_i; δ₁= (1/N)

U_i, δ₂= (1/N)

U $\genfrac{}{}{0ex}{}{\text{2}}{\text{i}}$ ;
U_i, I_i действующие значения падения напряжения на электролизере и ток серии, вызвавший эти падения, по каждой измеряемой гармонике, соответственно,
N количество отсчетов,
определяют составляющие комплексного сопротивления из системы уравнений:
R²+(X₁-X_c)²=(U/I)², при f₁
2R²+(2X₁-X_c/2)²=(U/I)², при f₂;
16R²+(4X₁-X_c/4)²=(U/I)², при f₃
где f₁ нижняя из частот, на которых производят измерения,
f₂, f₃ частоты, на которых производят измерения;
уточняют величину активного сопротивления по следующему математическому выражению:
R R/

где К=f/f_o коэффициент, учитывающий влияние скин-эффекта,
f частота измерения, f_o частота, на которой влиянием скин-эффекта можно пренебречь,
определяют величину обратной ЭДС по математическому выражению:
Е_о=U_э-I_cR_э;
определяют концентрацию глинозема по следующим математическим выражениям:
n=E_o/(I_cR_э); ν1/(eⁿ-1,4);
где n концентрация глинозема в относительных единицах,
ν концентрация глинозема в процентах;
определяют расстояние между анодом и катодом по следующему математическому выражению:
h_ак= κ R_э,
где κ Δ h/Δ R;
Δ R=R₁-R₂,
R₁= (1/N)

R_эi средняя величина активного сопротивления электролизера до перемещения анода,
R₂= (1/N)

R_эi cредняя величина активного сопротивления электролизера, после перемещения анода на расстояние Δ h. Существенным отличием предлагаемого технического решения является определение действующего значения тока серии каждой из измеряемых гармоник. Ранее эти величины определялись расчетным путем (через преобразование Фурье) с последующим уточнением путем ступенчатого снижения тока серии до нулевого уровня. Такая методика не исключала погрешностей в оценке величины гармонических составляющих тока серии, поскольку в процессе регулирования тока серии производят подключение либо отключение выпрямительных агрегатов в результате изменяется форма импульсов тока серии а, следовательно, и амплитуда гармоник, на которых ведут измерения перечисленных выше электрических параметров (составляющих комплексного сопротивления).The result of the solution of this problem is a method of controlling the technological parameters of aluminum electrolysis cells, including measuring the constant (U _e ) and variable components of the voltage drop across the cell and current (I _s ) series, calculating the resistance of the cell, and the measurements are performed simultaneously at harmonics that are multiples of 50 (60) Hz , according to the measurement results, determine the effective value of the variable component of the series current at each of the harmonics used for measurements, for which they determine the ratio, linking e measured current harmonics and a series of values of the voltage drop caused in each electrolyzer floor mathematical expression
I _f = aU _e ± b, (1)
where a = (r _o δ ₁ -Nr ₁ ) / (δ $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ -N δ ₂ );
b = (r ₁ δ ₁ -r _o δ ₂ ) / (δ $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ -N δ ₂ );
r _o = (1 / N)

I _i ;
r ₁ = (1 / N)

I _i U _i ; δ ₁ = (1 / N)

U _i , δ ₂ = (1 / N)

U $\genfrac{}{}{0ex}{}{\text{2}}{\text{i}}$ ;
U _i , I _{i the} effective values of the voltage drop across the electrolyzer and the series current that caused these drops, for each measured harmonic, respectively,
N number of samples
determine the components of complex resistance from a system of equations:
R ² + (X ₁ -X _c ) ² = (U / I) ² , for f ₁
2R ² + (2X ₁ -X _c / 2) ² = (U / I) ² , with f ₂ ;
16R ² + (4X ₁ -X _c / 4) ² = (U / I) ² , with f ₃
where f _{1 the} lower of the frequencies at which measurements are made,
f ₂ , f ₃ frequencies at which measurements are made;
specify the value of active resistance according to the following mathematical expression:
RR /

where K = f / f _o coefficient taking into account the effect of the skin effect,
f is the measurement frequency, f _{o is the} frequency at which the effect of the skin effect can be neglected,
determine the magnitude of the back EMF by mathematical expression:
E _o = U _e -I _c R _e ;
determine the concentration of alumina by the following mathematical expressions:
n = E _o / (I _c R _e ); ν1 / (e ⁿ -1.4);
where n is the concentration of alumina in relative units,
ν alumina concentration in percent;
determine the distance between the anode and cathode by the following mathematical expression:
h _ak = κ R _e ,
where κ Δ h / Δ R;
Δ R = R ₁ -R ₂ ,
R ₁ = (1 / N)

R _{ei the} average value of the active resistance of the cell to the movement of the anode,
R ₂ = (1 / N)

R _{ei is the} average value of the active resistance of the electrolyzer, after moving the anode to a distance Δ h. A significant difference of the proposed technical solution is the determination of the effective value of the series current of each of the measured harmonics. Previously, these values were determined by calculation (through the Fourier transform), followed by refinement by stepwise reducing the series current to zero. Such a technique did not exclude errors in estimating the magnitude of the harmonic components of the series current, since during the regulation of the series current the rectifier units are connected or disconnected, as a result, the shape of the series current pulses changes and, consequently, the amplitude of the harmonics used to measure the above electrical parameters (components integrated resistance).

 In addition, in the proposed solution to the problem, the harmonic current strength is found by determining the regression line by the least squares method, which makes it possible to determine the systematic error in measuring the components of the complex resistance. This systematic error corresponds to b. (see formula 1).

R_эi, Затем поднимают (опускают) анод на величину Δ h и вновь в течение выбранного интервала времени измеряют активное сопротивление электролизера
R₂= (1/N)

R_эi, Далее определяют коэффициент пропорциональности между сопротивлением электролизера и величиной межполюсного зазора
κ Δ h /Δ R,
где Δ R= R₁-R₂, и величину межполюсного расстояния h_ак= κ R, по результатам измерения текущего значения величины R_э за установленный интервал времени (1-3) ч. Это позволяет вести регулирование межполюсного зазора с точностью до 1 мм и добиваться оптимального выхода по току по данному параметру.The second significant difference is the measurement of the distance between the poles (the distance of the anode-cathode of the cell). To do this, measure electrical parameters and calculate the components of the complex resistance and the average value of the active resistance of the electrolyzer for a sufficiently long time interval (for example, 3 hours)
R ₁ = (1 / N)

R _ei , Then the anode is raised (lowered) by Δ h and again during the selected time interval the active resistance of the cell is measured
R ₂ = (1 / N)

R _ei , Next, determine the proportionality coefficient between the resistance of the cell and the magnitude of the interpolar gap
κ Δ h / Δ R,
where Δ R = R ₁ -R ₂ , and the magnitude of the interpolar distance h _ak = κ R, according to the results of measuring the current value of the quantity R _e for a specified time interval (1-3) hours. This allows you to adjust the interpolar gap with an accuracy of 1 mm and achieve the optimal current output for this parameter.

 The drawing shows a functional diagram of a device for implementing a method for monitoring the technological parameters of aluminum electrolytic cells (both with self-firing and with fired anodes).

The following notation is introduced in the drawing: 1 voltage switch anode-cathode of electrolyzers; 2 ₁ , 2 ₂ , 2 ₃ band-pass filters for extracting harmonics from the interpolar voltage and series current; 3 attenuator; 4 amplifiers; 5 detector; 6 voltage frequency converter; 7 galvanic isolation unit; 8 frequency-voltage converter; 9 analog-to-digital converter; 10 UVK; 11 series current harmonic current sensor; 12 shunt for measuring the DC component of the series current.

The device consists of two channels: a channel for measuring voltage drops in the anode-cathode section of the electrolyzer and a channel for measuring the series current. In the channel for measuring the voltage drop at the anode-cathode section of the cell, the input voltage switch 1 is connected by inputs to the sections of the anode-cathode of each cell, and by outputs to three band-pass filters 2 ₁ , 2 ₂ , 2 ₃ and to an automatic attenuator 3. The outputs of the band-pass filters through sequentially connected blocks of amplifiers 4, detectors 5, voltage frequency converters 6, galvanic isolation blocks 7, frequency voltage converters 8, are connected to the inputs of the ADC 9, the output of which is connected to the UVK 10. Automatic attenuation output torus 3 is connected to the input of the ADC 9 through series-connected blocks: voltage-frequency converter 6, galvanic isolation unit 7 and frequency-voltage converter 8.

In the second channel of measuring the current of the series, the induction sensor is connected to the inputs of the bandpass filters 2 ₁ , 2 ₂ , 2 ₃ , the outputs of which are connected to the ADC inputs, through series-connected blocks: amplifiers 4, detectors 5, voltage-frequency converters 6, galvanic isolation 7, frequency-voltage converters 8. The output of the shunt 11 is also connected to the input of the ADC 8 through series-connected blocks: the voltage converter frequency 6, galvanic isolation 7, and the frequency-voltage converter 8. The ADC output 9 is connected to the input of UVK 10.

The method is as follows: the signals taken from the sections of the anode-cathode of the electrolytic cells are fed to the input of the switch 1. The input switch 1 is controlled from UVK-10 and connects the inputs of the bandpass filters 2 ₁ , 2 ₂ , 2 ₃ and the automatic attenuator 3 to the selected for control electrolyzer. Bandpass filters 2 ₁ -2 _{3 are} tuned to harmonics multiple of the industrial frequency (50 or 60 Hz), for example 600, 1200, 2400 Hz. The automatic attenuator has two discrete signal transmission levels of 1: 1 and 10: 1. When switching to 10: 1 division, an additional logic signal is generated at an additional output connected to the UVK. The harmonic signals extracted by filters 2-2 are amplified to an amplitude value of 1 V, by amplifiers 4, detected by detectors 5, converted into a pulse repetition rate by voltage-frequency converters 6. The pulse repetition rate is proportional to the actual voltage value of the measured harmonics transmitted through galvanic isolation blocks 7 to the input frequency-voltage converters 8. The constant component of the voltage drop in the section of the anode-cathode ("working voltage" of the cell) from the output of the automatic attenuator 3 is fed to the input of the ADC 9 through series-connected blocks 6, 7, 8. The outputs of the frequency converter 8 are connected to the other inputs of the ADC 9. From the ADC output 9, the signals of the effective value of the harmonic components of the operating voltage of the electrolyzers are fed to the input of the air-conditioner 10. The channel works similarly series current measurements. A signal containing harmonics of the series current (600, 1200, 2400 Hz) is removed from the induction sensor 11 and fed to the inputs of the bandpass filters 2-2, from the output of which the converted signal is fed to the inputs of the ADC 9 through series-connected blocks 4, 5, 6, 7, 8. A signal proportional to the DC component of the current of series 1 is fed from shunt 12 to the input of the ADC-9 of the channel for measuring the series current through series-connected blocks 6, 7, 8. From the output of the ADC 9 (channel for measuring the current of the series), the signals are input UVK 10.

I_i;
r₁= (1/N)

I_iU_i; δ₁= (1/N)

U_i, δ₂= (1/N)

U $\genfrac{}{}{0ex}{}{\text{2}}{\text{i}}$ ;
U_i, I_i действующие значения падения напряжения на электролизере и ток серии, вызвавший эти падения, по каждой измеряемой гармонике соответственно,
N количество отсчетов.The sequence of implementation of the method is as follows. Having set the number of the interrogated electrolyzer using the input switch 1, simultaneous measurements of the effective current value and voltage drop in the anode-cathode section of the electrolyzer at three harmonics of the series current are started. At the same time, the constant components of the series current and the operating voltage of the electrolyzer are also measured. Measurements are taken with an interval exceeding the correlation time between samples. Having made 100-5000 samples (simultaneous measurements), the magnitude of the effective current value at each measured harmonic is determined from the equalities
I = aU ± b,
where a = (r _o δ ₁ -Nr) / (δ $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ -Nδ ₂ );
b = (r ₁ δ ₁ -r _o δ ₂ ) / (δ $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ -Nδ ₂ );
r _o = (1 / N)

I _i ;
r ₁ = (1 / N)

I _i U _i ; δ ₁ = (1 / N)

U _i , δ ₂ = (1 / N)

U $\genfrac{}{}{0ex}{}{\text{2}}{\text{i}}$ ;
U _i , I _{i the} effective values of the voltage drop across the cell and the series current that caused these drops, for each measured harmonic, respectively,
N is the number of samples.

где К=f/f_o коэффициент, учитывающий влияние скин-эффекта,
f частота измерения, f_o частота, на которой влиянием скин-эффекта можно пренебречь,
определяют величину обратной ЭДС по математическому выражению:
E_o=U_э-I_сR_э;
определяют концентрацию глинозема по следующим математическим выражениям:
n=E_o/(I_cR_э); ν=1/(eⁿ-1,4);
где n концентрация глинозема в относительных единицах,
ν концентрация глинозема в процентах.Having determined (having specified) the values of the current strength of each harmonic at which measurements are carried out, they again perform simultaneous measurements of current and voltage to determine the technological parameters. Based on the results of these measurements, the components R, X ₁ , X _c , and the complex resistance of the electrolyzer are found from the system of equations
R ² + (X ₁ -X _c ) ² = (U / I) ² , with f ₁ ;
4R ² + (2X ₁ -X _c / 2) ² = (U / I) ² , with f ₂ ;
16R ² + (4X ₁ -X _c / 4) ² = (U / I) ² , with f ₃ ;
where f _{1 the} lower of the frequencies at which measurements are made,
f ₂ , f ₃ frequencies at which measurements are made;
specify the value of active resistance according to the following mathematical expression:
R _e = R /

where K = f / f _o coefficient taking into account the effect of the skin effect,
f is the measurement frequency, f _{o is the} frequency at which the effect of the skin effect can be neglected,
determine the magnitude of the back EMF by mathematical expression:
E _o = U _e -I _with R _e ;
determine the concentration of alumina by the following mathematical expressions:
n = E _o / (I _c R _e ); ν = 1 / (e ⁿ -1.4);
where n is the concentration of alumina in relative units,
ν alumina concentration in percent.

R_эi среднюю величину активного сопротивления электролизера (R_i) до перемещения анода, затем поднимают (опускают) анод на величину Δ h (например, 5-10 мм) и вновь в течение часа измеряют активное сопротивление электролизера;
R₂= (1/N)

R_эi средняя величина активного сопротивления электролизера, после перемещения анода на расстояние Δ h.For relative concentration units, a conventional scale is adopted: n <0.5 high concentration level, 0.5 <n <0.65 nominal concentration level, n> 0.65 critical concentration level. At the next stage, calibration measurements are made of the magnitude of the interpolar distance. Measure R _e for the selected time interval (1-3) h. Having received for this interval N = 100-1000 measurements, find
R ₁ = (1 / N)

R _{ei the} average value of the active resistance of the electrolyzer (R _i ) before moving the anode, then raise (lower) the anode by the value Δ h (for example, 5-10 mm) and again within an hour measure the active resistance of the cell;
R ₂ = (1 / N)

R _{ei the} average value of the active resistance of the cell, after moving the anode to a distance Δ h.

The results are used to determine the coefficient of proportionality between R _e and h _ak :
κ Δ h / Δ R;
where Δ R = R ₁ -R ₂ .

Having received the relationship between R _e and h _ak , determine the true value
h _ak = κ R _e ,
according to the results of averaging R _e for the interval between two bath treatments, and when monitoring electrolyzers equipped with APG (automatic alumina feeders), for the set time interval for adjusting the MPR.

Claims (1)

METHOD FOR CONTROLING TECHNOLOGICAL PARAMETERS OF ALUMINUM ELECTROLYZERS, including measuring the constant U _e and the variable components of the voltage drop across the cell and current J _c ^u series, calculating the resistance of the cell, and the measurements are performed simultaneously at harmonics that are multiples of 50 Hz, and the value of the back EMF is different from the measurements the fact that they determine the effective value of the variable component of the series current at each of the harmonics used for measurements, for which they determine the ratio, linking its measured values of the harmonics of the series current, and the voltage drop caused by them on each cell according to the mathematical expression
I $\genfrac{}{}{0ex}{}{\text{~}}{\text{f}}$ = aU ^~ ± b;

J _i • U _i ;

U _i , I _{i the} effective values of the voltage drop across the cell and the series current that caused these drops, for each measured harmonic, respectively;
N number of samples
determine the components of complex resistance from a system of equations
R ² (X _L -X _C ) ² = (U ^~ / I ^~ ) ² for f ₁ ;
4R ² + (2X _L -X _C / 2) ² = (U ^~ / I ^~ ) ² for f ₂ ;
16R ² + (4X _L -X _C / 4) ² = (U ^~ / I ^~ ) ² for f ₃ ,
where f _{1 the} lower of the frequencies at which measurements are made;
f ₂ , f ₃ frequencies at which measurements are made,
specify the value of active resistance by mathematical expression

where K = f / f ₀ coefficient taking into account the effect of the skin effect;
f _{0 the} frequency at which the influence of the skin effect can be neglected,
determine the value of the back EMF by mathematical expression
E ₀ U _e I _c • R _e ,
determine the concentration of alumina by mathematical expressions

where n is the concentration of alumina, rel. units η alumina concentration,
determine the distance between the anode and cathode by mathematical expression
h _a-k = κ • R _e ,
where κ = Δh / ΔR;

the average value of the active resistance of the cell before moving the anode;

the average value of the active resistance of the cell after moving the anode to a distance Δh.

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