Primary aluminum quality control method for electrolytic cell

Abstract

The invention provides a primary aluminum quality control method for an electrolytic cell, and aims to solve the problem. In the prior art, when an anode is replaced, the stability of the electrolysis process is not controlled. The primary aluminum quality control method comprises the following steps: dynamically adjusting an electrolyte, and regularly detecting the ratio of NaF to AlF in the electrolyte; impurity ions are controlled, and the total concentration of the impurity ions in the electrolyte is controlled to be smaller than 0.5 wt%; according to the anode replacement strategy, before replacement, the current density near an anode is reduced, and after replacement, the current density is recovered to the standard current density; feedback adjustment is conducted, the impurity content in the molten aluminum is detected regularly through a plurality of sampling openings formed in the bottom of the electrolytic cell, and if the impurity content is detected to exceed the standard continuously and repeatedly, an electrolyte adjustment program is started; and a diversion trench and a microporous structure are arranged at the bottom of the electrolytic cell. Before the anode is replaced, the current density near the anode is reduced, so that local thermal field fluctuation and molten aluminum disturbance are effectively reduced, and the stability of molten aluminum is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolytic aluminum, in particular to a method for controlling the quality of primary aluminum in an electrolytic cell. BACKGROUND

[0002] In a large pre-baked electrolytic cell, the quality of primary aluminum is affected by many factors, such as electrolyte composition fluctuation, uneven anode operation, unstable thermal field distribution, etc. Among them, the electrolyte composition (such as molecular ratio, impurity ion concentration) and the current disturbance during anode replacement are the key factors affecting the content of impurities such as iron and silicon in the aluminum liquid. In the prior art, although there are measures to detect the electrolyte composition regularly and make adjustments, there is a lack of control means for the stability of the electrolysis process during anode replacement, resulting in large fluctuations in the content of impurities in the aluminum liquid, affecting the consistency and stability of the quality of primary aluminum. SUMMARY

[0003] In view of the technical problem in the prior art that there is a lack of control of the stability of the electrolysis process when replacing the anode, the present application provides a method for controlling the quality of primary aluminum in an electrolytic cell, which effectively reduces the local thermal field fluctuation and aluminum liquid disturbance by reducing the current density near the anode before replacing the anode, and improves the stability of the aluminum liquid.

[0004] The technical solution of the present application is as follows:

[0005] A method for controlling the quality of primary aluminum in an electrolytic cell, comprising:

[0006] dynamically adjusting the electrolyte, and regularly detecting the ratio of NaF to AlF3 in the electrolyte;

[0007] controlling impurity ions, and controlling the total concentration of impurity ions in the electrolyte to be less than 0.5wt%;

[0008] anode replacement strategy, before replacement, reducing the current density near the anode, and after replacement, restoring to the standard current density;

[0009] feedback adjustment, regularly detecting the content of impurities in the aluminum liquid through a plurality of sampling ports arranged at the bottom of the electrolytic cell, and if the content of impurities is continuously detected for multiple times, starting the electrolyte adjustment program;

[0010] optimizing the flow state of the aluminum liquid at the bottom of the electrolytic cell, and arranging a flow guide groove and a microporous structure at the bottom of the electrolytic cell.

[0011] Optionally, in the dynamic adjustment of the electrolyte, the molar ratio of NaF to AlF3 is in the range of 2.15±0.05.

[0012] Optionally, the dynamic adjustment of the electrolyte specifically comprises:

[0013] Set the detection cycle of every 72 hours, sample detection of the middle and four corners of the electrolytic cell area, determine the content of NaF and AlF3, and calculate the molar ratio;

[0014] If the molar ratio of NaF and AlF3 in the detection result is less than 2.1, NaF is added for adjustment;

[0015] If the molar ratio of NaF and AlF3 in the detection result is higher than 2.2, AlF3 is added for adjustment.

[0016] Optionally, when the total concentration of impurity ions is greater than or equal to 0.5wt%, a purification agent containing BaO is added, and the addition amount of the purification agent is controlled at 0.1wt%-0.3wt%.

[0017] Optionally, when the purification agent is added, the purification agent is mixed with the electrolyte powder at a ratio of 1:100, and then uniformly scattered into the electrolyte layer in the electrolytic cell;

[0018] After adding the purification agent, the current density of the electrolytic cell is maintained below 0.85A / cm² for 48 hours, and then part of the electrolyte is replaced, and the replacement amount is not more than 10% of the total amount of electrolyte.

[0019] Optionally, in the anode replacement strategy, the current density of the replaced area is reduced by 15.78%-18.75% within 1 hour before replacement to 2 hours after completion of replacement.

[0020] In the process of restoring the current density, the current density is restored by one-third per hour.

[0021] Optionally, in the anode replacement strategy, the diagonal replacement method is used to replace the anode, and after the replacement is completed, the electrolyte near the replaced anode is supplemented.

[0022] Optionally, in the feedback adjustment, the content of iron and silicon in the aluminum liquid is mainly detected, and ICP-OES method is used for quantitative analysis;

[0023] If the iron content exceeds 80ppm or the silicon content exceeds 30ppm for two consecutive times, the electrolyte adjustment program is started;

[0024] Optionally, the electrolyte adjustment program is: according to the exceeding element, selectively adding NaF, AlF3 or purification agent.

[0025] Optionally, in the optimization of the flow state of the aluminum liquid at the bottom of the electrolytic cell,

[0026] A plurality of longitudinal flow guide grooves are arranged at the bottom of the electrolytic cell, and a matrix distribution of micro-holes is arranged;

[0027] The flow rate of the molten aluminum in the flow guide groove is 0.05-0.1 m / s.

[0028] Compared with the prior art, the application has the following beneficial effects:

[0029] By precisely adjusting the electrolyte composition, the dissolution and migration of impurities such as iron and silicon in the molten aluminum are inhibited, and the purity of the primary aluminum is improved.

[0030] By controlling the total concentration of impurity ions, the activity of impurity ions in the electrolyte is reduced, and the purity of the primary aluminum is improved.

[0031] By reducing the current density near the anode before replacing the anode, the local thermal field fluctuation and the disturbance of the molten aluminum are effectively reduced, and the stability of the molten aluminum is improved.

[0032] By feedback adjustment and cooperation with the control of impurity ions and anode replacement strategy, a dynamic adjustment system of the primary aluminum quality is formed to ensure the stable and controllable product quality. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0034] Figure 1 The process method of the present application is shown in the schematic diagram.

[0035] Figure 2 The structure of the bottom of the electrolytic cell is shown in the schematic diagram. DETAILED DESCRIPTION

[0036] In the following, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application. Therefore, the drawings and description are considered to be exemplary in nature rather than limiting.

[0037] The following disclosure provides many different embodiments, or examples, for implementing different structures of the present application. For the purpose of simplification, the elements and arrangements of the particular examples are described in the following disclosure. Of course, they are merely examples and are not intended to limit the present application. In addition, the present application can repeatedly refer to reference numerals and / or reference letters in different examples, and such repetition is for the purpose of simplification and clarity, which does not indicate the relationship between the various embodiments and / or arrangements discussed. In addition, the present application provides examples of various specific processes and materials, but those skilled in the art can realize the application of other processes and / or the use of other materials.

[0038] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0039] Embodiments:

[0040] Referring to Figure 1 The present embodiment discloses a method for controlling the quality of primary aluminum in an electrolytic cell, which comprises dynamically adjusting the electrolyte, controlling impurity ions, anode replacement strategy, feedback adjustment and optimizing the flow state of molten aluminum at the bottom of the electrolytic cell, so as to improve the purity of primary aluminum, the stability of molten aluminum and ensure the stable and controllable product quality.

[0041] Specifically, dynamically adjusting the electrolyte means that during the production of electrolytic aluminum, the molar ratio of NaF and AlF3 in the electrolyte is detected regularly (usually once every 72 hours) to control the ratio of the two, so that the molar ratio of the two is within the dynamic range of 2.15±0.05.

[0042] During sampling, the middle position and the four corner positions of the electrolytic cell are mainly sampled respectively, and the sample amount collected is consistent. The position setting during sampling is to improve the accuracy of the detection result, so that the sample is representative.

[0043] During the detection of the sample, the X-ray fluorescence spectrometer (XRF) is used to determine the content of NaF and AlF3, and the molar ratio of the two is calculated.

[0044] If the molar ratio of NaF and AlF3 in the detection result is less than 2.1, NaF is added to the electrolytic cell in batches for adjustment. If the molar ratio of NaF and AlF3 in the detection result is greater than 2.2, AlF3 is added to the electrolytic cell in batches for adjustment.

[0045] When adding NaF or AlF3 into the electrolytic cell, the powder-like NaF or AlF3 is added, and the amount of each addition is not more than 0.3% (generally 0.25%) of the total amount of electrolyte, and the time interval of each addition is not less than four hours. After adding NaF or AlF3 into the electrolytic cell, the anode operation is suspended for at least one hour to ensure that the newly added NaF or AlF3 is fully mixed in the electrolyte, and the sampling and re-inspection of the aluminum liquid are completed within 24 hours after the addition to ensure the stability of the molecular ratio.

[0046] By controlling the operation of impurity ions, the total concentration of impurity ions in the electrolyte is less than 0.5wt%, thereby reducing the activity of impurity ions in the electrolyte and improving the purity of the primary aluminum.

[0047] Specifically, this step mainly controls the total concentration of Ca²⁺, Mg²⁺, and Fe³⁺ in the electrolyte. When the total concentration of impurity ions in the electrolyte is greater than or equal to 0.5wt%, a purifying agent containing BaO is added to the electrolyte, wherein the content of BaO in the purifying agent is not less than 60%, and the addition amount of the purifying agent needs to be controlled in the range of 0.1wt%-0.3wt%, and the electrolyte replacement or adjustment is completed within 48 hours after the addition to prevent the enrichment of impurity ions during the electrolysis process and affect the quality of the aluminum liquid.

[0048] Specifically, when adding the purifying agent, the purifying agent is mixed with the electrolyte powder at a ratio of 1:100, and then uniformly scattered into the electrolyte layer in the electrolytic cell. After adding the purifying agent, the current density of the electrolytic cell is maintained below 0.85A / cm² for 48 hours, and then part of the electrolyte is replaced, and the replacement amount is not more than 10% of the total amount of electrolyte.

[0049] The method of controlling impurity ions is to generate precipitates by chemical reaction to reduce the activity of impurity ions and improve the purification ability of the electrolyte.

[0050] The aforementioned anode replacement strategy can effectively reduce the local thermal field fluctuation and aluminum liquid disturbance caused by replacing the anode, and improve the stability of the aluminum liquid.

[0051] Specifically, the current density in the area near the anode to be replaced is reduced by 15.78%-18.75% within one hour before replacing the anode and two hours after replacing the anode. After two hours of replacement, the current density is gradually restored at a rate of one-third of the current density per hour until it returns to the standard current density.

[0052] In actual production lines, the standard current density is 0.85A / cm²-0.95A / cm², and the current density is reduced to 0.7A / cm²-0.8A / cm² within one hour before replacement and two hours after replacement. During the recovery process, the current density is gradually restored at a rate of 0.5A / cm² per hour.

[0053] The time for replacing a single anode is controlled within 15 minutes, and the electrolyte should not be disturbed violently during the replacement.

[0054] During the whole replacement process, the infrared thermometer is used to monitor the temperature change of the anode area, and ensure that the local temperature difference after replacement is not more than 15°C.

[0055] For the whole electrolytic cell, during the replacement of the anode, the diagonal replacement method is adopted, specifically, all the anodes are numbered in the form of rows and columns, and each time the anodes are replaced in a diagonal distribution state with the anodes replaced last time.

[0056] In addition, in order to ensure that the thermal field has enough recovery time, the number of anodes replaced in each electrolytic cell per day is not more than 3. After the replacement is completed, the electrolyte in the replacement area is supplemented, and the supplement amount is 100kg-150kg per anode. After the end of each replacement period (one replacement period is that all the anodes in the electrolytic cell are replaced once), the thermal imager is used to draw the temperature distribution map of the bottom of the electrolytic cell, and ensure that the temperature gradient change is less than 5℃ / m.

[0057] The replacement method significantly improves the uniformity of the internal thermal field of the electrolytic cell through spatial distribution optimization.

[0058] In the feedback regulation, the impurity content in the aluminum liquid is detected regularly through the multiple sampling ports set at the bottom of the electrolytic cell, and if the impurity content is continuously detected for multiple times, the electrolyte adjustment program is started.

[0059] Specifically, 6 equidistant sampling ports are set at the bottom of the electrolytic cell, and aluminum liquid sampling is performed every 72 hours, quantitative analysis is performed by ICP-OES method, and the contents of iron and silicon in the aluminum liquid are detected. If the iron content is detected for two times continuously more than 80ppm or the silicon content is detected for two times continuously more than 30ppm, the electrolyte adjustment program is started.

[0060] The electrolyte adjustment program specifically is: according to the element exceeding the standard, selectively adding NaF, AlF3 or purifying agent, and adjusting the replacement order of the anode. The second sampling is performed within 48 hours after the electrolyte adjustment program to verify the control effect.

[0061] The feedback regulation realizes dynamic closed-loop control of the aluminum liquid quality through periodic detection and process parameter adjustment.

[0062] Optimizing the flow state of the aluminum liquid at the bottom of the electrolytic cell mainly is to reduce the residence time of the aluminum liquid at the bottom of the electrolytic cell, and reduce the impurity deposition, including setting multiple flow guide grooves and a plurality of micropore structures at the bottom of the electrolytic cell.

[0063] Specifically, as shown in FIG. 6, a plurality of flow guide grooves 601 are set at the bottom of the electrolytic cell, and a plurality of micropore structures 602 are set in the flow guide grooves 601. Figure 2As shown, three longitudinal (along the length direction of the electrolytic cell) flow guide grooves 20 are equidistantly arranged at the bottom of the electrolytic cell 10, the depth of the flow guide groove 20 is 50 mm, the width is 80 mm, and the distance between adjacent flow guide grooves 20 is 1.2 m.

[0064] A plurality of micropores 30 are arranged at the bottom of the electrolytic cell 10, the diameter of the micropore 30 is 2 mm, and all the micropores 30 are arranged in a matrix structure. The distance between adjacent two micropores 30 is 100 mm, and the micropore 30 can promote the circulation of the aluminum liquid.

[0065] The flow state of the aluminum liquid is controlled: by adjusting the anode current distribution, the flow rate of the aluminum liquid in the flow guide groove 20 is maintained at 0.05 m / s-0.1 m / s. After the electrolytic cell 10 works for a certain period of time, the aluminum liquid flow field needs to be simulated to ensure that the standard deviation of the flow rate is less than 0.02 m / s.

[0066] The structure design significantly reduces the risk of local enrichment of impurity elements by optimizing the flow path of the aluminum liquid.

[0067] The above method is implemented in a certain 300 kA pre-baked electrolytic cell, and after 3 months of operation, the test results are as follows:

[0068] The iron content in the aluminum liquid is reduced from an average of 92 ppm to 68 ppm, and the fluctuation range is reduced from ±15 ppm to ±8 ppm;

[0069] The silicon content is reduced from an average of 35 ppm to 22 ppm, and the fluctuation range is reduced from ±10 ppm to ±5 ppm;

[0070] The electrolyte molecular ratio is stably maintained in the range of 2.15±0.03, and the electrolyte replacement frequency is reduced by 30%;

[0071] The local temperature fluctuation caused by anode replacement is reduced from an average of 25°C to within 12°C.

[0072] The embodiment significantly improves the stability and consistency of the primary aluminum quality through the synergistic control of multiple process parameters, and has good industrial application prospect.

[0073] The above-described embodiments only express the specific implementation of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A method for quality control of primary aluminum in an electrolytic cell, characterized in that, include: The electrolyte was dynamically adjusted, and the ratio of NaF to AlF3 in the electrolyte was periodically monitored. Control impurity ions, ensuring the total concentration of impurity ions in the electrolyte is less than 0.5 wt%. The anode replacement strategy involves reducing the current density near the anode before replacement and restoring it to the standard current density after replacement. Feedback adjustment involves periodically detecting the impurity content in the molten aluminum through multiple sampling ports located at the bottom of the electrolytic cell. If the impurity content exceeds the standard after multiple consecutive tests, the electrolyte adjustment program is activated. To optimize the flow state of molten aluminum at the bottom of the electrolytic cell, guide channels and microporous structures are set at the bottom of the electrolytic cell.

2. The control method according to claim 1, characterized in that, In the dynamically adjusted electrolyte, the molar ratio of NaF to AlF3 is within the range of 2.15 ± 0.

05.

3. The control method according to claim 2, characterized in that: The dynamic adjustment of the electrolyte specifically includes: A testing cycle of once every 72 hours is set up to sample and test the areas in the middle and four corners of the electrolytic cell, determine the content of NaF and AlF3, and calculate the molar ratio. If the molar ratio of NaF to AlF3 in the test results is less than 2.1, then add NaF to adjust it; If the molar ratio of NaF to AlF3 in the test results is higher than 2.2, then add AlF3 to adjust it.

4. The control method according to claim 1, characterized in that, When the total concentration of impurity ions is greater than or equal to 0.5 wt%, a purifying agent containing BaO is added, and the amount of purifying agent added is controlled between 0.1 wt% and 0.3 wt%.

5. The control method according to claim 4, characterized in that: When adding the purifying agent, mix the purifying agent and electrolyte powder at a ratio of 1:100, and then evenly sprinkle it into the electrolyte layer in the electrolytic cell. After adding the purifying agent, maintain the current density of the electrolytic cell below 0.85 A / cm² for 48 hours, then replace part of the electrolyte, with the replacement amount not exceeding 10% of the total electrolyte.

6. The control method according to claim 1, characterized in that: In the aforementioned anode replacement strategy, the current density in the anode replacement area decreases by 15.78%-18.75% within 1 hour before replacement and 2 hours after replacement. During the recovery process, the current density is gradually restored using a strategy of restoring one-third of the current density per hour.

7. The control method according to claim 6, characterized in that, In the anode replacement strategy, the anode is replaced using a diagonal replacement method. After the replacement is completed, electrolyte is replenished in the area near the replaced anode.

8. The control method according to claim 1, characterized in that: In the feedback regulation, the main detection of iron and silicon content in the molten aluminum is carried out by quantitative analysis using ICP-OES. If the iron content exceeds 80 ppm or the silicon content exceeds 30 ppm in two consecutive tests, the electrolyte adjustment procedure will be initiated.

9. The control method according to claim 8, characterized in that, The electrolyte adjustment procedure is as follows: depending on the element exceeding the standard, selectively add NaF, AlF3, or a purifying agent.

10. The control method according to claim 1, characterized in that, In the optimized flow state of the molten aluminum at the bottom of the electrolytic cell: Multiple longitudinal guide channels are set at the bottom of the electrolytic cell, and micropores are arranged in a matrix distribution. The flow velocity of the molten aluminum in the guide channel is controlled between 0.05 m / s and 0.1 m / s.

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