CN112575349A - Aluminum oxide blanking and concentration control method for aluminum electrolysis cell - Google Patents
Aluminum oxide blanking and concentration control method for aluminum electrolysis cell Download PDFInfo
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Abstract
The invention relates to a method for controlling alumina blanking and concentration, in particular to a method for controlling alumina blanking and concentration of an aluminum electrolysis cell in the field of aluminum electrolysis. After the lower limit of the alumina concentration is determined in the undercharging-overcasting period, the concentration in the groove reaches the target concentration, then the standard charging period is carried out, the initial charging speed is given when the standard charging period starts, the polar distance of the resistor is subjected to polar distance increasing compensation for multiple times in the standard charging period, and the charging speed is adjusted in real time between the two polar distance compensations. The invention has the advantages and effects that: the invention controls the concentration change of the electrolytic cell in a required specified small range, can effectively reduce thermal shock of frequent over-under blanking to the electrolyte temperature and the superheat degree, corrects the alumina concentration and the polar distance through an intermittent under-over blanking period, prevents the concentration from drifting, provides a polar distance compensation means and realizes the precise control of the polar distance balance of the electrolytic cell. Because the precise control of the concentration and the polar distance of the alumina is realized, the current efficiency is favorably improved, and the real-time efficiency of the electrolytic cell can be evaluated according to the reference blanking rate change curve of the whole day.
Description
Technical Field
The invention relates to a method for controlling alumina blanking and concentration, in particular to a method for controlling alumina blanking and concentration of an aluminum electrolysis cell in the field of aluminum electrolysis.
Technical Field
In the production process of aluminum electrolysis, the blanking and concentration control of alumina are carried out in an excess and deficiency alternating mode, the alumina concentration of the whole cell is controlled between an upper limit and a lower limit to carry out periodic change, as shown in figure 1, the theoretical basis is the characteristic curve relation of the alumina concentration and the cell resistance, and the control method is generally applied to aluminum electrolysis enterprises. In recent years, with the increasing capacity and size of the electrolytic cell, indexes such as current efficiency and direct current consumption are difficult to meet ideal requirements, and the main problems are mainly reflected in two aspects of alumina concentration and polar distance control.
1. Alumina concentration control
The modern large-scale prebaked aluminum electrolysis cell is difficult to accurately determine a reference blanking rate (equal to the consumption rate of alumina in a certain time) matched with the current efficiency, and only through the alternative control of excess and deficiency (blanking modes higher than and lower than the reference blanking rate), the alumina concentration of the whole cell is controlled within a certain range (generally 1.5-3.5%). This traditional control mode can have various adverse effects on the electrolytic production: the high concentration area can not dissolve alumina in time due to over high local concentration, so that precipitation even furnace bottom hard crusting is formed, horizontal current in aluminum liquid is increased, and the stability of the electrolytic cell is influenced; the low concentration area can increase the possibility of a flicker effect and even a full-cell effect due to the over-low concentration of the local alumina, increase the energy consumption and reduce the current efficiency; the periodic variation of the excess and deficiency in the electrolytic cell frequently causes the impact on the superheat degree of the electrolyte, the local heat balance and the interface stability, and the current efficiency is lost.
2. Polar distance control
In the normal production of the electrolytic cell, the consumption rate of the anode height and the growth rate of the aluminum liquid thickness growth are not balanced, and the consumption of the anode is
Wherein h iscThe anode consumption rate (cm/d), danodeAs the anodic current density (A/cm)2) CE is the current efficiency (%), wcFor the anode consumption (kg/t-Al), dcIs the anode bulk density (g/cm)2) The growth height of the aluminum liquid is
Wherein h is the growth height (cm) of the aluminum liquid, m is the mass (g) of the aluminum liquid, and rho is the density (g/cm) of the aluminum liquid3) And S1 is the upper surface area (cm) of the volume of the aluminum liquid2) S2 is the lower surface area (cm) of the volume of the aluminum liquid2). Generally, the consumption rate of the anodes in various groove types is smaller than the growth rate of the aluminum liquid, so that the polar distance height (the distance from the bottom surface of the anode to the upper surface of the aluminum liquid) is continuously reduced if the concentration of aluminum oxide is unchanged and no anode acts in the production process. In contrast, the conventional control mode is realized by monitoring the cell voltage, that is, when the cell voltage is lower than a certain voltage value, the anode is lifted, and the pole distance is pulled. In fact, the variation of the cell voltage is mainly composed of two parts: the change of the electrode distance resistance voltage drop caused by the change of the electrode distance height and the change of the concentration voltage drop caused by the change of the alumina concentration (including the change of the resistivity caused by the change of the concentration and the change of the reaction overvoltage) jointly determine the change of the whole electrode distance of the electrolytic cell. This makes it difficult to achieve the precise control of alumina concentration and polar distance simultaneously only by cell voltage in production control.
In order to solve the above problems, patent ZL 201110166650.X proposes a control mode mainly based on a normal blanking period, so as to keep the alumina concentration within a substantially constant range, so as to reduce the influence of alumina concentration variation. Patent ZL 201110372135.7 further expands the method by adjusting the amount of each point of blanking in combination with the distribution of anodic current, to achieve a spatially uniform distribution of alumina concentration. The control basis of the two patents is still to realize the control of the alumina concentration according to the cell voltage, and no clear solution is provided for the problem of the polar distance control. In the control mode referred to in the patent, as the electrode distance is gradually reduced as the electrolysis proceeds, the alumina 'concentration drop' of the electrolyte continues to be high under only the cell voltage control, causing the alumina concentration to drift toward the effect region, increasing the possibility of the anode effect occurring.
The conventional control mode and the control mode proposed in the patent at present are difficult to realize the constant control of the alumina concentration and the polar distance of the ultra-large aluminum electrolysis cell.
Disclosure of Invention
The invention provides an aluminum oxide blanking and concentration control method for an aluminum electrolytic cell, aiming at accurately controlling the concentration and the polar distance of aluminum oxide and improving the current efficiency.
In order to achieve the aim, the invention provides an aluminum electrolysis cell alumina blanking and concentration control method, which comprises the steps of determining the lower limit or the upper limit of the alumina concentration in an under-passing blanking period, enabling the concentration in a cell to reach a target concentration, then entering a reference blanking period, giving an initial blanking rate when the reference blanking period starts, carrying out multiple times of pole lifting compensation on a resistance pole distance in the reference blanking period, and carrying out real-time adjustment on the blanking rate between two times of pole distance compensation.
The under-over blanking period comprises an under period and an over period, wherein after the lower limit of the alumina concentration is determined in the under period, the concentration is corrected, and after a period of over blanking, the concentration in the groove reaches the target concentration, and then the standard blanking period is started.
The under-and-over blanking period comprises an under period and an over period, wherein after the under period determines the lower limit of the alumina concentration, the upper limit of the alumina concentration is determined through the over period, double correction of the concentration is carried out, and after a period of under blanking, the concentration in the groove reaches the target concentration, and then the groove enters the standard blanking period.
The under-and-over blanking period comprises an under period and an over period, wherein after the upper limit of the concentration of the aluminum oxide is determined in the over period, the concentration is corrected, and after a period of under blanking, the concentration in the groove reaches the target concentration, the groove enters a reference blanking period.
The under-passing blanking period comprises an under period and an over period, after the upper limit of the alumina concentration is determined in the over period, the lower limit of the alumina concentration is determined in the under period, double correction of the concentration is carried out, and after a period of over blanking is carried out, the concentration in the groove reaches the target concentration and then enters the reference blanking period.
The alumina concentration in the cell is brought to the target concentration by controlling the voltage or the time under/over.
The under-passing blanking period and the reference blanking period are a cycle period, and the cycle period is 3-12 hours.
The upper limit of the concentration of the alumina is 2.2-3.0%, and the lower limit of the concentration of the alumina is 1.5-1.8%.
And the initial blanking rate is determined according to the current efficiency calculation of the previous day or the reference blanking interval before pole changing.
The real-time adjustment of the reference blanking rate is that when the cell concentration is unchanged, the reference blanking rate is adjusted in real time according to the cell voltage change rate dV/dt: adjusting NB to NB- Δ NB when (dV/dt-C) x Δ t > σ; and when (dV/dt-C) multiplied by delta t < -sigma, adjusting NB to be NB + delta NB, wherein C is the theoretical slope of the voltage change caused by the change of the polar distance, delta t is the calculated time step, sigma is the allowed voltage error, NB reference blanking time interval, and delta NB fine adjustment amount in each time interval.
And when aluminum discharging is carried out during the standard blanking period, stopping the real-time adjustment calculation of the blanking rate of the aluminum oxide, carrying out constant-rate blanking by adopting a standard blanking interval NB before aluminum discharging, and restarting the real-time adjustment calculation of the blanking rate after the aluminum discharging is finished.
And when the reference blanking rate is adjusted in real time, the reference blanking rate is adjusted in real time according to the change rate dV/dt of the tank voltage: adjusting NB to NB- Δ NB when (dV/dt). times.Δ t > σ; and when (dV/dt) multiplied by delta t < -sigma, adjusting NB to be NB + delta NB, wherein delta t is the calculated time step, sigma is the allowed voltage error, NB reference blanking time interval, and delta NB each time interval fine adjustment quantity.
The aluminum electrolysis cell alumina blanking and concentration control method also comprises a pole changing period, and an under-passing and over-blanking period is started after the pole changing period is finished.
The whole blanking rate before pole changing is taken in the pole changing period, concentration correction is carried out in the under-passing and over-blanking period after pole changing is finished, and a new period is started; and after the new pole is replaced, the blanking amount of the blanking port close to the new pole is reduced, and the alumina blanking amount is compensated by other blanking ports of the half-tank where the blanking port is positioned.
The blanking amount of the blanking port close to the new pole is gradually increased along with the pole changing time, such as 20% blanking after 1-3 hours after pole changing, 50% blanking after 4-8 hours after pole changing, 80% blanking after 9-16 hours after pole changing, and 100% blanking after 16 hours after pole changing.
And the reduced blanking amount of the blanking opening close to the new pole after pole changing is compensated by alumina through other blanking openings of the half-tank where the blanking opening is positioned.
And pole distance compensation is carried out in the reference blanking period in each cycle period.
The polar distance compensation is polar lifting compensation, a lifting mechanism is utilized to lift the anode large bus regularly, and the anode consumption h of one day is calculatedcThe growth height h of the aluminum liquid, and the difference (h-h) between the growth height h and the growth height h of the aluminum liquidc) And obtaining the distance of lifting the anode in the reference blanking period in each cycle period according to the difference.
The invention has the advantages and effects that: the invention controls the concentration change of the electrolytic cell in a required specified small range, can effectively reduce thermal shock of frequent over-under blanking to the electrolyte temperature and superheat degree, corrects the concentration and the polar distance of the aluminum oxide through the under-over blanking period, prevents the concentration from drifting, provides a polar distance compensation means, and realizes the precise control of the polar distance balance of the electrolytic cell. Because the precise control of the concentration and the polar distance of the alumina is realized, the current efficiency is favorably improved, and the real-time efficiency of the electrolytic cell can be evaluated according to the reference blanking rate change curve of the whole day.
Drawings
FIG. 1 is a characteristic graph of conventional alumina concentration versus cell resistance.
Fig. 2 is a logic control diagram of a constant concentration control mode for half cycles of the run-down period followed by the run-up period.
FIG. 3 is a logic control diagram of a full cycle constant concentration control scheme with an underrun period followed by an overrun period.
Fig. 4 is a logic control diagram of a constant voltage control mode for half cycles of the underrun period followed by the overrun period.
FIG. 5 is a logic control diagram of a full cycle constant voltage control scheme with starvation and then overshoot periods.
Fig. 6 is a logic control diagram of a constant concentration control mode for half cycles of the over period followed by the under period.
FIG. 7 is a logic control diagram of a full cycle constant concentration control scheme with an excess period followed by an deficiency period.
Fig. 8 is a logic control diagram of a constant voltage control mode for half cycles of an over period followed by an under period.
FIG. 9 is a logic control diagram of a full cycle constant voltage control scheme with an over period followed by an under period.
FIG. 10 is a schematic view of a feed opening of a 500kA electrolytic cell.
In the figure: 1. a first feed opening; 2. a second feed opening; 3. a third feed opening; 4. a fourth feed opening; 5. a fifth feed opening; 6. and a sixth feed opening.
Detailed Description
The invention will be further explained with reference to the drawings.
Example 1
As shown in figure 2, the aluminum electrolysis cell alumina blanking and concentration control method comprises a pole changing period, an under-passing blanking period is entered after the pole changing period is finished, the under-passing blanking period comprises an under period and an over period, the under-passing blanking period is a half period, the under period is first followed by the over period, after the lower limit of the alumina concentration is determined in the under-passing blanking period, the cell concentration reaches a target concentration and then enters a standard blanking period, an initial blanking rate is given when the standard blanking period starts, the resistance pole distance is subjected to multiple times of pole-lifting compensation in the standard blanking period, and the blanking rate is adjusted in real time between two pole distance compensations.
The concentration of alumina in the cell is controlled to a target concentration by controlling the voltage so that the upper limit of the concentration of alumina is 2.5% and the lower limit of the concentration of alumina is 1.7%. The under-passing blanking period and the reference blanking period are a cycle period, and the cycle period is 12 hours.
The initial blanking rate is determined by current efficiency calculation on the previous day.
The real-time adjustment of the reference blanking rate is that when the cell concentration is not changed, the reference blanking rate is adjusted in real time according to the cell voltage change rate dV/dt: adjusting NB to NB- Δ NB when (dV/dt-C) x Δ t > σ; and when (dV/dt-C) multiplied by delta t < -sigma, adjusting NB to be NB + delta NB, wherein C is the theoretical slope of the voltage change caused by the change of the polar distance, delta t is the calculated time step, sigma is the allowed voltage error, NB reference blanking time interval, and delta NB fine adjustment amount in each time interval.
Taking a 500kA electrolytic cell as an example, the real-time adjustment of the reference blanking rate is detailed:
if the slope C of the voltage change caused by the change of the polar distance is-0.0024 millivolts/second, the calculated time step delta t is 10 seconds, the allowed voltage error sigma is 5 millivolts, the reference blanking time interval NB is 72 seconds, and the fine adjustment quantity delta NB of each time interval is 0.2 seconds.
If the change rate dV/dt of the tank voltage is 1.3 millivolts/second, (dV/dt-C) multiplied by delta t is more than 5 millivolts, and the reference blanking time interval is adjusted from 72 seconds to 71.8 seconds; if the change rate dV/dt of the tank voltage is 0 millivolt/second, then (dV/dt-C) multiplied by delta t is less than 5 millivolts and more than-5 millivolts, and the reference blanking time interval is not adjusted for 72 seconds; if the cell voltage change rate dV/dt is-1.4 mV/s, then (dV/dt-C). times.DELTA.t is less than-5 mV, and then the reference blanking interval is adjusted from 72 seconds to 72.2 seconds.
And stopping the real-time adjustment calculation of the alumina blanking rate when the aluminum is discharged in the reference blanking period, and restarting the real-time adjustment calculation of the blanking rate after the aluminum discharging is finished. Taking the integral blanking rate before pole changing in the pole changing period, carrying out concentration correction in the under-passing-over blanking period after pole changing is finished, and starting a new period; and after the new pole is replaced, the blanking amount of the blanking port close to the new pole is reduced, and the alumina blanking amount is compensated by other blanking ports of the half-tank where the blanking port is positioned. The blanking amount of the blanking port close to the new pole is 20 percent of blanking after 1 to 3 hours after pole changing, 50 percent of blanking after 4 to 8 hours after pole changing, 80 percent of blanking after 9 to 16 hours after pole changing and 100 percent of blanking after 16 hours after pole changing. And after the electrode is changed, the reduced blanking amount of the blanking opening close to the new electrode is compensated by alumina through other blanking openings of the half-tank where the blanking opening is positioned.
As shown in fig. 10, the amount of the material discharged from the discharge opening close to the new electrode after the electrode change is reduced, and the alumina compensation is performed by the other discharge openings of the half tank in which the discharge opening is located. Taking a 500kA electrolytic cell as an example: if the anode A1 and the anode A2 are changed, the pole changing position is close to the first feed opening 1, the blanking amount of the first feed opening 1 is reduced, and the blanking rates of the second feed opening 2 and the third feed opening 3 in the same area are increased for compensation; if the anode B15 and the anode B16 are changed, the pole changing position is close to the fourth feed opening 4, the feeding amount of the fourth feed opening 4 is reduced, and the feeding speed of the fifth feed opening 5 and the sixth feed opening 6 in the same area is increased to compensate.
The pole pitch compensation is explained in detail by taking a 500kA electrolytic cell as an example:
consumption of the anode h as one dayc1.8cm, the growth height h of the aluminum liquid is 2.4cm, and the difference value between the two is 6 mm. The electrolytic production is divided into 2 circulation periods 24 times a day, and the polar distance of 3mm is compensated in the basic blanking period within 12 hours of each period.
Example 2
As shown in figure 3, the aluminum cell alumina blanking and concentration control method comprises a pole changing period, an under-passing period is entered after the pole changing period is finished, the under-passing period comprises an under period and an over period, the under-passing period is a full period, the under period is first followed by the over period, the lower limit of the alumina concentration is determined in the under period, the alumina concentration upper limit is determined in the over period, double correction of the concentration is carried out, the under blanking is carried out for a period of time, the cell concentration reaches the target concentration and then entered into a reference blanking period, the initial blanking rate is set when the reference blanking period is started, multiple times of pole lifting compensation are carried out on the resistance pole distance in the reference blanking period, and the real-time adjustment of the blanking rate is carried out between the two pole distance compensations.
The concentration of alumina in the cell is controlled to a target concentration by controlling the voltage so that the upper limit of the alumina concentration is 3.0% and the lower limit of the alumina concentration is 1.8%. The under-passing blanking period and the reference blanking period are a cycle period, and the cycle period is 8 hours.
The initial blanking rate is determined according to the reference blanking interval before pole changing.
The real-time adjustment of the reference blanking rate is that when the cell concentration is not changed, the reference blanking rate is adjusted in real time according to the cell voltage change rate dV/dt: adjusting NB to NB- Δ NB when (dV/dt-C) x Δ t > σ; and when (dV/dt-C) multiplied by delta t < -sigma, adjusting NB to be NB + delta NB, wherein C is the theoretical slope of the voltage change caused by the change of the polar distance, delta t is the calculated time step, sigma is the allowed voltage error, NB reference blanking time interval, and delta NB fine adjustment amount in each time interval.
Taking a 400kA electrolytic cell as an example, the real-time adjustment of the reference blanking rate is detailed:
if the slope C of the voltage change caused by the change of the polar distance is-0.0023 millivolts/second, the calculated time step delta t is 15 seconds, the allowed voltage error sigma is 8 millivolts, the reference blanking time interval NB is 68 seconds, and the fine adjustment quantity delta NB of each time interval is 0.5 second.
If the change rate dV/dt of the tank voltage is 0.9 millivolt/second, the (dV/dt-C) multiplied by delta t is more than 8 millivolts, and the reference blanking time interval is adjusted from 68 seconds to 67.5 seconds; if the change rate dV/dt of the tank voltage is 0.2 millivolt/second, the (dV/dt-C) multiplied by delta t is less than 8 millivolts and more than-8 millivolts, and the reference blanking time interval is not adjusted for 68 seconds; if the cell voltage change rate dV/dt is-1.1 mV/s, then (dV/dt-C). times.DELTA.t is less than-8 mV, and then the reference blanking interval is adjusted from 68 seconds to 68.5 seconds. The pole pitch compensation is explained in detail by taking a 400kA electrolytic cell as an example:
consumption of the anode h as one dayc1.8cm, the growth height h of the aluminum liquid is 2.6cm, and the difference value between the two is 8 mm. The electrolytic production is divided into 3 cycle periods every 24 hours, and the polar distance of 2.67mm is compensated in the standard blanking period within 8 hours of each cycle.
Otherwise, the same procedure as in example 1 was repeated.
Example 3
As shown in fig. 4, in example 1, the under-passing period is a half period, the upper limit of the alumina concentration is 2.7%, the lower limit of the alumina concentration is 1.8%, the cycle period is 6 hours, and when the reference blanking rate is adjusted in real time so that the cell voltage is not changed, the reference blanking rate is adjusted in real time according to the cell voltage change rate dV/dt: adjusting NB to NB- Δ NB when (dV/dt). times.Δ t > σ; and when (dV/dt) multiplied by delta t < -sigma, adjusting NB to be NB + delta NB, wherein delta t is the calculated time step, sigma is the allowed voltage error, NB reference blanking time interval, and delta NB each time interval fine adjustment quantity.
Taking a 500kA electrolytic cell as an example, the real-time adjustment of the reference blanking rate is detailed:
if the calculated time step Δ t is taken to be 20 seconds, the allowed voltage error σ is 12 millivolts, the reference blanking time interval NB is 70.2 seconds, and the fine adjustment amount Δ NB of each time interval is 0.1 second.
If the change rate dV/dt of the tank voltage is 1.5 millivolts/second, (dV/dt) × deltat is more than 12 millivolts, and the reference blanking time interval is adjusted to 70.1 seconds from 70.2 seconds; if the change rate dV/dt of the tank voltage is 0.05 millivolts/second, then (dV/dt) multiplied by delta t is less than 12 millivolts and more than-12 millivolts, and the reference blanking time interval is not adjusted for 70.2 seconds; if the cell voltage change rate dV/dt is-1.2 mV/s, then (dV/dt) × Δ t is less than-12 mV, and then the reference blanking time interval is adjusted from 70.2 s to 70.3 s.
And stopping the real-time adjustment calculation of the alumina blanking rate when the aluminum discharging is carried out during the standard blanking period, and restarting the real-time adjustment calculation of the blanking rate after the aluminum discharging is finished. Taking the integral blanking rate before pole changing in the pole changing period, carrying out concentration correction in the under-passing-over blanking period after pole changing is finished, and starting a new period; and after the new pole is replaced, the blanking amount of the blanking port close to the new pole is reduced, and the alumina blanking amount is compensated by other blanking ports of the half-tank where the blanking port is positioned. The feed rate near the feed opening of the new pole gradually increases in a linear fashion from 20% to 100% feed over 16 hours. And after the electrode is changed, the reduced blanking amount of the blanking opening close to the new electrode is compensated by alumina through other blanking openings of the half-tank where the blanking opening is positioned.
The pole pitch compensation is explained in detail by taking a 500kA electrolytic cell as an example:
consumption of the anode h as one dayc1.8cm, the growth height h of the aluminum liquid is 2.4cm, and the difference value between the two is 6 mm. The electrolytic production is divided into 4 cycle periods in 24 time per dayWithin 6 hours, a pole pitch of 1.5mm is compensated within a basic blanking period.
Otherwise, the same procedure as in example 1 was repeated.
Example 4
As shown in fig. 5, the under-passing period in example 1 is a full period, the upper limit of the alumina concentration is 2.8%, the lower limit of the alumina concentration is 1.7%, and one cycle period is 4 hours, after the lower limit of the alumina concentration is determined in the under period, the upper limit of the alumina concentration is determined in the over period, double correction of the concentration is performed, after a period of under-passing is performed, the concentration in the tank reaches the target concentration, and then the tank enters a reference blanking period, and when the tank voltage is not changed by real-time adjustment of the reference blanking rate, the reference blanking rate is adjusted in real time according to the tank voltage change rate dV/dt: adjusting NB to NB- Δ NB when (dV/dt). times.Δ t > σ; and when (dV/dt) multiplied by delta t < -sigma, adjusting NB to be NB + delta NB, wherein delta t is the calculated time step, sigma is the allowed voltage error, NB reference blanking time interval, and delta NB each time interval fine adjustment quantity.
Taking a 300kA electrolytic cell as an example, the real-time adjustment of the reference blanking rate is detailed:
if the calculated time step Δ t is taken to be 30 seconds, the allowed voltage error σ is 15 millivolts, the reference blanking time interval NB is 72.5 seconds, and the fine adjustment amount Δ NB of each time interval is 0.1 second.
If the change rate dV/dt of the tank voltage is 0.9 millivolt/second, the (dV/dt) multiplied by delta t is larger than 15 millivolts, and the reference blanking time interval is adjusted from 72.5 seconds to 72.4 seconds; if the change rate dV/dt of the tank voltage is 0.1 millivolt/second, the (dV/dt) multiplied by delta t is less than 15 millivolts and more than-15 millivolts, and the reference blanking time interval is not adjusted for 72.5 seconds; if the cell voltage change rate dV/dt is-1.2 mV/s, then (dV/dt) × Δ t is less than-15 mV, and then the reference blanking time interval is adjusted from 72.5 seconds to 72.6 seconds.
The pole pitch compensation is explained in detail by taking a 300kA electrolytic cell as an example:
consumption of the anode h as one dayc1.8cm, the growth height h of the aluminum liquid is 2.8cm, and the difference value between the two is 10 mm. The electrolytic production is divided into 6 cycle periods at 24 time per day, and the period is 4 hours per cycleThe pole distance of 2.5mm is compensated in the blanking period.
Otherwise, the same procedure as in example 1 was repeated.
Example 5
The invention relates to an aluminum oxide blanking and concentration control method for an aluminum electrolytic cell, which comprises the steps of determining the lower limit of the aluminum oxide concentration in an under-passing blanking period, enabling the concentration in the cell to reach a target concentration, entering a reference blanking period, giving an initial blanking rate when the reference blanking period starts, carrying out multiple electrode-increasing compensation on a resistance polar distance in the reference blanking period, and carrying out real-time adjustment on the blanking rate between the two electrode distance compensations. The under-over blanking period comprises an under period and an over period, the under-over blanking period is a half period,
the concentration of alumina in the cell is controlled to a target concentration by controlling the voltage so that the upper limit of the concentration of alumina is 2.2% and the lower limit of the concentration of alumina is 1.5%. The under-passing blanking period and the reference blanking period are a cycle period, and the cycle period is 3 hours.
The initial blanking rate is determined by current efficiency calculation on the previous day.
The real-time adjustment of the reference blanking rate is that when the cell concentration is not changed, the reference blanking rate is adjusted in real time according to the cell voltage change rate dV/dt: adjusting NB to NB- Δ NB when (dV/dt-C) x Δ t > σ; and when (dV/dt-C) multiplied by delta t < -sigma, adjusting NB to be NB + delta NB, wherein C is the theoretical slope of the voltage change caused by the change of the polar distance, delta t is the calculated time step, sigma is the allowed voltage error, NB reference blanking time interval, and delta NB fine adjustment amount in each time interval.
Taking a 500kA electrolytic cell as an example, the real-time adjustment of the reference blanking rate is detailed:
if the slope C of the voltage change caused by the change of the polar distance is-0.0025 millivolts/second, the calculated time step delta t is taken to be 20 seconds, the allowed voltage error sigma is 10 millivolts, the reference blanking time interval NB is 73 seconds, and the fine adjustment quantity delta NB of each time interval is 0.2 seconds.
If the change rate dV/dt of the tank voltage is 1.2 millivolts/second, (dV/dt-C) multiplied by delta t is more than 10 millivolts, and the reference blanking time interval is adjusted from 73 seconds to 72.8 seconds; if the change rate dV/dt of the tank voltage is-0.1 millivolt/second, the (dV/dt-C) multiplied by delta t is less than 10 millivolts and more than-10 millivolts, and the reference blanking time interval is not adjusted for 73 seconds; if the cell voltage change rate dV/dt is-1.3 mV/s, then (dV/dt-C). times.DELTA.t is less than-10 mV, and then the reference blanking time interval is adjusted from 73 seconds to 73.2 seconds.
The pole pitch compensation is explained in detail by taking a 500kA electrolytic cell as an example:
consumption of the anode h as one dayc1.8cm, the growth height h of the aluminum liquid is 2.4cm, and the difference value between the two is 6 mm. The electrolytic production was divided into 8 cycles at 24 hours per day, with a pole pitch of 0.75mm offset in the baseline blanking period for 3 hours per cycle.
Otherwise, the same procedure as in example 1 was repeated.
Example 6
As shown in fig. 6, the starved-overflowed period in example 1 is the overdue period first and then the starved period. Otherwise, the same procedure as in example 1 was repeated.
Example 7
As shown in fig. 7, the starved-overflowed period in example 2 is the overdue period first and then the starved period. Otherwise, the same procedure as in example 1 was repeated.
Example 8
As shown in fig. 8, the starved-overflowed period in example 3 is the overdue period first and then the starved period. Otherwise, the same procedure as in example 1 was repeated.
Example 9
As shown in fig. 9, the starved-overdue period in example 4 is the overdue period first and then the starved period. Otherwise, the same procedure as in example 1 was repeated.
Claims (18)
1. A method for controlling alumina blanking and concentration of an aluminum electrolytic cell is characterized in that after the lower limit or the upper limit of the alumina concentration is determined in an under-passing blanking period, the concentration in the cell reaches a target concentration and then enters a reference blanking period, an initial blanking rate is given when the reference blanking period starts, multiple pole-lifting compensation is carried out on a resistance pole distance in the reference blanking period, and the blanking rate is adjusted in real time between the two pole distance compensations.
2. The aluminum oxide blanking and concentration control method for the aluminum electrolytic cell according to claim 1, wherein the under-passing blanking period comprises an under period and an over period, the concentration is corrected after the lower limit of the aluminum oxide concentration is determined in the under period, and the aluminum oxide blanking period is started after a period of time of over blanking to make the concentration in the aluminum electrolytic cell reach the target concentration.
3. The aluminum oxide blanking and concentration control method for the aluminum electrolytic cell according to claim 1, characterized in that the under-passing blanking period comprises an under period and an over period, after the lower limit of the aluminum oxide concentration is determined in the under period, the upper limit of the aluminum oxide concentration is determined in the over period, the concentration is double corrected, and after a period of under blanking, the concentration in the cell reaches the target concentration and then enters the reference blanking period.
4. The aluminum oxide blanking and concentration control method for the aluminum electrolytic cell according to claim 1, wherein the under-passing blanking period comprises an under period and an over period, the concentration is corrected after the upper limit of the aluminum oxide concentration is determined in the over period, and the reference blanking period is started after the under blanking is performed for a period of time to make the concentration in the cell reach the target concentration.
5. The aluminum oxide blanking and concentration control method for the aluminum electrolytic cell according to claim 1, characterized in that the under-passing blanking period comprises an under period and an over period, after the over period determines the upper limit of the aluminum oxide concentration, a under period determines the lower limit of the aluminum oxide concentration, double correction of the concentration is performed, and after a period of over blanking, the aluminum oxide concentration in the cell reaches the target concentration and then enters the reference blanking period.
6. A method for blanking and controlling the alumina concentration of an aluminum reduction cell according to claim 2, 3, 4 or 5, characterized in that the alumina concentration in the cell is controlled to the target concentration by controlling the voltage or the time of shortage/excess.
7. The method for controlling alumina blanking and concentration of aluminum reduction cells according to claim 2, 3, 4 or 5, wherein the under-passing blanking period and the reference blanking period are a cycle period, and one cycle period is 3-12 hours.
8. The aluminum electrolysis cell alumina blanking and concentration control method according to claim 3 or 5, characterized in that the upper limit of the alumina concentration is 2.2-3.0%, and the lower limit of the alumina concentration is 1.5-1.8%.
9. The method as claimed in claim 1, wherein the initial blanking rate is determined by current efficiency calculation of the previous day or by a reference blanking interval before pole changing.
10. The method as claimed in claim 9, wherein the real-time adjustment of the reference blanking rate is performed according to the cell voltage variation rate dV/dt when the cell concentration is constant, and the reference blanking rate is adjusted in real time according to the cell voltage variation rate dV/dt: when (dV/dt-C) Δ t > σ, adjust NB to be NB- Δ NB; when (dV/dt-C) Δ t < - σ, adjusting NB to NB +. NB, wherein C is the theoretical slope of the voltage change caused by the change of the polar distance, Δ t is the calculated time step size taken, σ is the allowed voltage error, NB is the blanking time interval of the reference, and the fine adjustment amount of each time interval of the NB is.
11. The method as claimed in claim 10, wherein the real-time adjustment calculation of the alumina blanking rate is stopped during the baseline blanking period, the constant-rate blanking is performed by using the baseline blanking interval NB before the aluminum discharge, and the real-time adjustment calculation of the blanking rate is restarted after the aluminum discharge is finished.
12. The method as claimed in claim 9, wherein the real-time adjustment of the reference blanking rate is performed in such a way that the reference blanking rate is adjusted in real time according to the cell voltage change rate dV/dt when the cell voltage is not changed: when (dV/dt) Δ t > σ, adjust NB to Δ NB; when (dV/dt) Δ t < - σ, adjusting NB to NB +. NB, where Δ t is the calculated time step taken, σ is the allowed voltage error, NB reference blanking time interval, and the amount of fine adjustment of each time interval of NB.
13. The aluminum oxide blanking and concentration control method for the aluminum electrolytic cell as recited in claim 1, further comprising a pole-changing period, and entering an under-passing blanking period after the pole-changing period is over.
14. The aluminum oxide blanking and concentration control method for the aluminum electrolytic cell according to claim 13, characterized in that the overall blanking rate before pole changing is taken during the pole changing period, after the pole changing is finished, the concentration correction is performed during the under-out period, and a new period is started; and after the new pole is replaced, the blanking amount of the blanking port close to the new pole is reduced, and the alumina blanking amount is compensated by other blanking ports of the half-tank where the blanking port is positioned.
15. The method as claimed in claim 14, wherein the blanking amount of the blanking port near the new pole is gradually increased with the pole changing time, such as 20% blanking in 1-3 hours after pole changing, 50% blanking in 4-8 hours after pole changing, 80% blanking in 9-16 hours after pole changing, and 100% blanking in 16 hours after pole changing.
16. The method as claimed in claim 15, wherein the amount of the aluminum oxide discharged from the discharge opening near the new electrode is reduced after electrode replacement, and the aluminum oxide compensation is performed by the other discharge openings of the half-cell in which the discharge opening is located.
17. The method as claimed in claim 7, wherein the pole pitch compensation is performed during the standard blanking period of each cycle.
18. The aluminum electrolysis cell alumina blanking and concentration control method as recited in claim 17, wherein the pole pitch compensation is an anode lifting compensation, the anode large bus is lifted by the lifting mechanism at regular time, and the one-day anode consumption is calculatedh c The growth height of the aluminum liquidhCalculating the difference between the two values (h-h c ) And obtaining the distance of lifting the anode in the reference blanking period in each cycle period according to the difference.
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