Method for calculating the amount of aluminium fluoride to be added in an aluminium electrolysis cell

Abstract

The application discloses a calculation method of the adding amount of aluminum fluoride in an aluminum electrolysis cell, which comprises the following steps: calculating the net mass of electrolyte, the single-cell maintaining amount of the electrolysis cell, the target molecular ratio K2 of the electrolysis cell, the theoretical daily adding amount of aluminum fluoride, the calibration coefficient, the neutralizing amount of aluminum fluoride required for changing the sodium content in the input series alumina and the sodium content in the balanced alumina, the parameter modification value of the electrolysis cell client, and the adding amount of aluminum fluoride. The material and energy balance principles are comprehensively considered, and the sodium content and the fluorine content in the raw materials are also considered, the relatively low molecular ratio is selected under the premise of the stability of the electrolysis cell, and the technical and economic indexes of the electrolysis cell operation are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum electrolysis, in particular to a calculation method of aluminum fluoride addition amount in an aluminum electrolysis cell. BACKGROUND

[0002] In the aluminum electrolysis process, the electrolyte is the solvent of the aluminum electrolysis cell and is the "blood" of the aluminum electrolysis reaction, which bears the heavy responsibility of conducting electricity, dissolving alumina and maintaining heat balance. The addition of aluminum fluoride in the aluminum electrolysis cell can reduce the electrolyte molecular ratio (the molar ratio of sodium fluoride and aluminum fluoride), improve the electrolyte properties and increase the current efficiency. At present, there is no systematic calculation method for the addition amount of aluminum fluoride in the industry, and each enterprise adds it according to its own habits, lacking professional analysis system or reference basis. Too little aluminum fluoride addition amount will lead to an increase in the molecular ratio, an increase in the electrolyte temperature and a decrease in the current efficiency of the electrolysis cell, and too much aluminum fluoride addition amount will lead to a sharp decrease in the molecular ratio, a decrease in the stability of the electrolysis cell and the dissolution performance of alumina, ultimately resulting in a decrease in the current efficiency and an increase in the unit consumption of aluminum fluoride. Therefore, reasonable addition of aluminum fluoride is not only an important factor for maintaining the stability of the electrolyte composition and the stable operation of the electrolysis cell, but also an effective way to optimize the technical and economic indicators and reduce material consumption.

[0003] At present, the material of the constant-volume discharging device used in aluminum electrolysis is ordinary steel, which is easily affected by the magnetic field and may be magnetized during use, and the discharging amount is unstable. Moreover, the adjustment of the molecular ratio by the operating personnel is based on the traditional method of first theoretical calculation and then correction of the theoretical addition amount according to the site conditions and experience, which will result in low precision of the aluminum fluoride addition amount and large fluctuation of the molecular ratio, seriously affecting the stability of the electrolysis cell operation. In addition, the underpass ratio, electrolyte temperature, electrolysis cell needle vibration and swing will all affect the addition amount of aluminum fluoride. SUMMARY

[0004] The present application provides a calculation method of aluminum fluoride addition amount in an aluminum electrolysis cell, aiming to reasonably add aluminum fluoride, maintain the stability of the electrolyte composition and ensure the stable operation of the electrolysis cell.

[0005] The present application is a calculation method of aluminum fluoride addition amount in an aluminum electrolysis cell, characterized by comprising the following steps:

[0006] (1) calculating the net mass of the electrolyte

[0007] The net mass of the electrolyte = the net volume capable of containing the electrolyte × the density of the electrolyte;

[0008] The net volume capable of containing the electrolyte = the volume of the reaction zone of the electrolysis cell + the volume between the anodes in the electrolysis cell - the volume on the small machining surface of the electrolysis cell - the volume on the large machining surface of the electrolysis cell - the volume of the anode;

[0009] Wherein, the electrolytic cell reaction zone volume = (electrolytic cell hearth net length - 2 x electrolytic cell furnace wall thickness) x (electrolytic cell hearth net width - 2 x electrolytic cell furnace wall thickness) x electrode distance;

[0010] The electrolytic cell anode-to-anode volume = (electrolytic cell hearth net length - 2 x electrolytic cell furnace wall thickness) x (electrolytic cell hearth net width - 2 x electrolytic cell furnace wall thickness) x (electrolyte horizontal height - electrode distance between anode and cathode);

[0011] The electrolytic cell small machining surface volume = (electrolytic cell small machining surface width - electrolytic cell furnace wall thickness) x electrolyte horizontal height x (electrolytic cell hearth net width - 2 x electrolytic cell furnace wall thickness);

[0012] The electrolytic cell large machining surface volume = (electrolytic cell large machining surface width - electrolytic cell furnace wall thickness) x electrolyte horizontal height x (electrolytic cell hearth net length - 2 x electrolytic cell furnace wall thickness);

[0013] The anode volume = anode net length x anode net width x (electrolyte horizontal height - electrode distance between anode and cathode) x anode block number;

[0014] (2) Calculate the electrolytic cell single-slot maintenance amount

[0015] The electrolytic cell single-slot maintenance amount = single-slot efficiency x aluminum electrochemical equivalent x 24h x electrolytic series current x reference consumption amount of aluminum fluoride;

[0016] (3) Calculate the electrolytic cell target molecular ratio K2

[0017] K2(CR)=(NaF mass / Naf molecular weight+LiF mass / LiF molecular weight+KF mass / KF molecular weight+CaF2 mass / CaF2 molecular weight-MgF2 mass / MgF2 molecular weight) / ALF3 mass / ALF3 molecular weight;

[0018] (4) Calculate the theoretical daily adjustment amount of aluminum fluoride

[0019] The theoretical daily adjustment amount of aluminum fluoride = the theoretical weekly adjustment amount of aluminum fluoride / 7;

[0020] The theoretical weekly adjustment amount of aluminum fluoride = (2 x total amount of pure cryolite x (K1-K2)) / (K2 x (K1+2));

[0021] The total amount of pure cryolite = net mass of electrolyte x (1-total impurity content / 100);

[0022] Wherein: K1 is the actual molecular ratio of the electrolytic cell; the total impurity content is the total content of CaF2, KF, MgF2, LiF, AL2O3, NaO in the electrolyte;

[0023] (5) Calculate the calibration coefficient

[0024] The calibration coefficient is calculated according to the theoretical discharge amount of the single-tank aluminum fluoride volumetric feeder and the weighing and approval result of the actual discharge amount of the aluminum fluoride volumetric feeder, and the calibration coefficient = the theoretical discharge amount of the single-tank aluminum fluoride / the actual discharge amount of the single-tank aluminum fluoride;

[0025] (6) Calculate the amount of aluminum fluoride required for neutralizing the change in sodium content in the balance alumina

[0026] a. The sodium content in the series alumina = (the amount of alumina input x the sodium content in the alumina) / the total input amount;

[0027] b. The amount of aluminum fluoride required for neutralizing the change in sodium content in the balance alumina = (the actual sodium content in the alumina - the average sodium content) x the daily alumina discharge amount x the molecular weight of ALF3 / 2.4 / the molecular weight of NaF / 100;

[0028] (7) Calculate the parameter modification value of the electrolytic cell client

[0029] The parameter modification value of the electrolytic cell client = the daily addition amount of aluminum fluoride x the calibration coefficient;

[0030] The daily addition amount of aluminum fluoride = the single-tank maintenance amount of the electrolytic cell + the theoretical daily adjustment amount of aluminum fluoride + the amount of aluminum fluoride required for neutralizing the change in sodium content in the balance alumina;

[0031] The addition amount of aluminum fluoride is the parameter modification value of the electrolytic cell client.

[0032] Preferably, when the under-over ratio changes, the addition amount of aluminum fluoride is corrected, and the addition amount of aluminum fluoride is increased or decreased by 2 kg for each increase or decrease of 0.01 in the under-over ratio.

[0033] Preferably, when the electrolyte temperature changes, the addition amount of aluminum fluoride is corrected, and the addition amount of aluminum fluoride is increased or decreased by 2 kg for each increase or decrease of 2℃ in the electrolyte temperature within a range of 5℃.

[0034] Preferably, when the needle vibration of the electrolytic cell changes, the addition amount of aluminum fluoride is corrected, and the addition amount of aluminum fluoride is decreased by 2 kg when the needle vibration value of the electrolytic cell is 5-10 mv, the addition amount of aluminum fluoride is decreased by 10 kg when the needle vibration value of the electrolytic cell is 10-20 mv, and the addition amount of aluminum fluoride is halved when the needle vibration value of the electrolytic cell is 20 mv or more.

[0035] Preferably, when the swing of the electrolytic cell changes, the addition amount of aluminum fluoride is corrected, and the addition amount of aluminum fluoride is decreased by 2 kg when the swing value of the electrolytic cell is 2-5 mv, the addition amount of aluminum fluoride is decreased by 10 kg when the swing value of the electrolytic cell is 6-10 mv, and the addition amount of aluminum fluoride is halved when the swing value of the electrolytic cell is 10 mv or more.

[0036] Compared with the prior art, the present application has the following advantages:

[0037] 1. The calculation method of the aluminum fluoride addition amount in the aluminum electrolysis cell provided by the present application comprehensively considers the material and energy balance principles, and takes into account the individual properties of the electrolysis cell, as well as the changes in the sodium content and the fluorine content in the raw materials, and selects a relatively low molecular ratio under the premise of electrolysis cell stability, thereby greatly improving the technical and economic indicators of the electrolysis cell operation. The impurity content in the electrolyte is included in the calculation formula, which improves the accuracy of the calculation method and the adaptability to changes in raw materials. After popularization and use, the molar ratio of sodium fluoride to aluminum fluoride is stably maintained at about 2.4, the series runs stably, the aluminum fluoride consumption decreases month by month, and the direct current consumption is optimized month by month.

[0038] 2. The calculation method of the aluminum fluoride addition amount in the aluminum electrolysis cell provided by the present application is suitable for the case where the sealing bell of the aluminum fluoride constant-volume feeder is made of stainless steel structure, eliminates the influence of the strong magnetic field on the actual discharge amount of the constant-volume feeder, reduces the fluctuation of the molecular ratio of the single cell, and introduces a calibration coefficient of the constant-volume feeder to correct the adjustment amount, thereby better solving the problem of the difference in the constant volume of the aluminum fluoride constant-volume feeder.

[0039] 3. The calculation method of the aluminum fluoride addition amount in the aluminum electrolysis cell provided by the present application comprehensively considers the electrolyte temperature and the stability of the electrolysis cell and other influencing factors in the determination of the target molecular ratio and the aluminum fluoride addition amount, so as to reduce the molecular ratio when the electrolysis cell is stable and has low superheat, thereby achieving the purpose of high current efficiency; and the aluminum fluoride addition amount is reduced in time when the electrolysis cell fluctuates and the superheat increases, thereby preventing the melting of the electrolysis cell hearth caused by large fluctuations and the occurrence of the situation of deteriorated indicators. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with examples:

[0041] Taking a 500kA aluminum electrolysis cell as an example, the net length of the electrolysis cell hearth is 18510mm, the net width of the electrolysis cell hearth is 4450mm, the large machining surface width of the electrolysis cell is 200mm, the small machining surface width of the electrolysis cell is 375mm, the theoretical aluminum fluoride discharge amount of the electrolysis cell is 1.8kg, the net length of the anode used is 1850mm, the net width of the anode is 700mm, the number of anode blocks in the electrolysis cell is 48, and the density of the liquid electrolyte is 0.0000021g / mm 3, the field measurement of the thickness of the furnace side of the electrolytic cell is 110 mm, the field measurement of the distance between the anode and the cathode is 45 mm, the impurity content is detected by a fluorescence instrument and an atomic absorption instrument as follows: CaF2-4.31%, KF-1.89%, MgF2-1.01%, LiF-3.40%, AL2O3-2.06%, the addition amount of aluminum fluoride is calculated after the field measurement of the horizontal height of the electrolyte. The sealing bell of the aluminum fluoride constant volume feeder is a stainless steel structure. The specific calculation method is as follows:

[0042] (1) Calculate the net mass of the electrolyte

[0043] The net mass of the electrolyte = the net volume that can accommodate the electrolyte × the density of the electrolyte;

[0044] The net volume that can accommodate the electrolyte = the volume of the reaction zone of the electrolytic cell + the volume between the anodes in the electrolytic cell - the volume on the small machining surface of the electrolytic cell - the volume on the large machining surface of the electrolytic cell - the volume of the anode;

[0045] The volume of the reaction zone of the electrolytic cell = (the net length of the furnace hearth of the electrolytic cell - 2 × the thickness of the furnace side of the electrolytic cell) × (the net width of the furnace hearth of the electrolytic cell - 2 × the thickness of the furnace side of the electrolytic cell) × the distance between the anode and the cathode;

[0046] The volume between the anodes in the electrolytic cell = (the net length of the furnace hearth of the electrolytic cell - 2 × the thickness of the furnace side of the electrolytic cell) × (the net width of the furnace hearth of the electrolytic cell - 2 × the thickness of the furnace side of the electrolytic cell) × (the horizontal height of the electrolyte - the distance between the anode and the cathode);

[0047] The volume on the small machining surface of the electrolytic cell = (the width of the small machining surface of the electrolytic cell - the thickness of the furnace side of the electrolytic cell) × the horizontal height of the electrolyte × (the net width of the furnace hearth of the electrolytic cell - 2 × the thickness of the furnace side of the electrolytic cell);

[0048] The volume on the large machining surface of the electrolytic cell = (the width of the large machining surface of the electrolytic cell - the thickness of the furnace side of the electrolytic cell) × the horizontal height of the electrolyte × (the net length of the furnace hearth of the electrolytic cell - 2 × the thickness of the furnace side of the electrolytic cell);

[0049] The volume of the anode = the net length of the anode × the net width of the anode × (the horizontal height of the electrolyte - the distance between the anode and the cathode) × the number of anode blocks;

[0050] The calculation results are shown in Table 1:

[0051] Table 1 Calculation of the net mass of the electrolyte

[0052]

[0053] (2) Calculate the single-cell maintenance amount of the electrolytic cell

[0054] The single-cell maintenance capacity of an electrolytic cell = single-cell efficiency × electrochemical equivalent of aluminum × 24h × electrolytic series current × baseline consumption of aluminum fluoride; where: the single-cell efficiency is 92%, the electrochemical equivalent of aluminum is 0.3355, the electrolytic series current is 500kA, and the baseline consumption of aluminum fluoride is 15.1kg / t·Al.

[0055] (3) Calculate the target molecular ratio K2 of the electrolyzer.

[0056] K2(CR) = (NaF mass / NaF molecular weight + LiF mass / LiF molecular weight + KF mass / KF molecular weight + CaF2 mass / CaF2 molecular weight - MgF2 mass / MgF2 molecular weight) / ALF3 mass / ALF3 molecular weight;

[0057] (4) Calculate the theoretical daily adjustment amount of aluminum fluoride.

[0058] The theoretical daily adjustment amount of aluminum fluoride = the theoretical weekly adjustment amount of aluminum fluoride / 7;

[0059] The theoretical weekly adjustment amount of the aluminum fluoride = (2 × total amount of pure cryolite × (K1 - K2)) / (K2 × (K1 + 2));

[0060] The total amount of pure cryolite = net mass of electrolyte × (1 - total impurity content / 100);

[0061] Where: K1 is the actual molecular ratio of the electrolyzer; the total impurity content is the total content of CaF2, KF, MgF2, LiF, Al2O3, and NaO in the electrolyte;

[0062] The calculation results are shown in Table 2:

[0063] Table 2 Theoretical Daily Adjustment of Aluminum Fluoride

[0064]

[0065] (5) Calculate the calibration coefficients

[0066] The aluminum fluoride constant volume feeder is weighed and verified once a week. The calibration coefficient is calculated based on the theoretical feed rate of the single tank aluminum fluoride constant volume feeder and the weekly weighing and verification results of the actual feed rate of the aluminum fluoride constant volume feeder. Calibration coefficient = theoretical feed rate of single tank aluminum fluoride / actual feed rate of single tank aluminum fluoride.

[0067] (6) Calculate the amount of aluminum fluoride required to neutralize the sodium content in the input alumina series and the change in sodium content in the equilibrium alumina.

[0068] a. Sodium content in alumina series = (Manufacturer's alumina input amount × Sodium content in manufacturer's alumina + Manufacturer's alumina input amount × Sodium content in manufacturer's alumina) / Total input amount;

[0069] b. The amount of aluminum fluoride required to balance the change in sodium content in alumina = (actual sodium content in alumina - average sodium content) x daily alumina discharge amount x molecular weight of ALF3 / 2.4 / molecular weight of NaF / 100;

[0070] (7) Calculate the parameter modification value of the electrolytic cell client

[0071] The parameter modification value of the electrolytic cell client = the daily addition amount of aluminum fluoride x the calibration coefficient;

[0072] The daily addition amount of aluminum fluoride = the single-cell maintenance amount + the theoretical daily adjustment amount of aluminum fluoride + the amount of aluminum fluoride required to balance the change in sodium content in alumina;

[0073] The current electrolytic cell is running normally, the undershoot ratio, electrolyte temperature, and electrolytic cell needle vibration and swing are normal, so no correction is made to the addition amount of aluminum fluoride, and the parameter modification value of the electrolytic cell client is the addition amount of aluminum fluoride.

[0074] The above calculation results are shown in Table 3:

[0075] Table 3: Calculation of the addition amount of aluminum fluoride

[0076]

[0077] After using this method in 500kA series aluminum electrolytic cells, the molar ratio of sodium fluoride to aluminum fluoride is stably maintained at about 2.4, the 500kA aluminum electrolysis runs stably, the needle vibration value of the electrolytic cell is less than 5mV, the swing value is less than 1.6mV, the unit consumption of aluminum fluoride is reduced month by month, reaching 15.1kg / t·Al, the direct current unit consumption of main indicators is optimized month by month, reaching 12305kWh / t·Al, and the electrolysis qualified rate reaches 97.92%. This method liberates technical personnel from tedious and dull cell control data analysis work, and reduces the work intensity.

Claims

1. A method of calculating the amount of aluminum fluoride to be added in an aluminum electrolysis cell, characterized by, It comprises the following steps: (1) Calculate the net mass of electrolyte Net mass of electrolyte = net volume of electrolyte that can be accommodated × electrolyte density; The net volume of electrolyte that can be accommodated = volume of electrolytic cell reaction zone + volume between anodes in electrolytic cell - volume on small machining surface of electrolytic cell - volume on large machining surface of electrolytic cell - volume of anode; Among them, the volume of electrolytic cell reaction zone = (net length of electrolytic cell hearth - 2 × thickness of electrolytic cell side wall) × (net width of electrolytic cell hearth - 2 × thickness of electrolytic cell side wall) × anode distance; The volume between anodes in electrolytic cell = (net length of electrolytic cell hearth - 2 × thickness of electrolytic cell side wall) × (net width of electrolytic cell hearth - 2 × thickness of electrolytic cell side wall) × (electrolyte level height - anode distance between cathode and anode); The volume on small machining surface of electrolytic cell = (small machining surface width of electrolytic cell - thickness of electrolytic cell side wall) × electrolyte level height × (net width of electrolytic cell hearth - 2 × thickness of electrolytic cell side wall); The volume on large machining surface of electrolytic cell = (large machining surface width of electrolytic cell - thickness of electrolytic cell side wall) × electrolyte level height × (net length of electrolytic cell hearth - 2 × thickness of electrolytic cell side wall); The volume of anode = net length of anode × net width of anode × (electrolyte level height - anode distance between cathode and anode) × anode block number; (2) Calculate the single-cell maintenance amount of electrolytic cell Single-cell maintenance amount of electrolytic cell = single-cell efficiency × electrochemical equivalent of aluminum × 24h × electrolytic series current × reference consumption amount of aluminum fluoride; (3) Calculate the target molecular ratio K2 of electrolytic cell K2(CR)=(NaF mass / NaF molecular weight+LiF mass / LiF molecular weight+KF mass / KF molecular weight+CaF2 mass / CaF2 molecular weight-MgF2 mass / MgF2 molecular weight) / ALF3 mass / ALF3 molecular weight; (4) Calculate the theoretical daily adjustment amount of aluminum fluoride Theoretical daily adjustment amount of aluminum fluoride = theoretical weekly adjustment amount of aluminum fluoride / 7; Theoretical weekly adjustment amount of aluminum fluoride = (2 × total amount of pure cryolite × (K1-K2)) / (K2×(K1+2)); Total amount of pure cryolite = net mass of electrolyte × (1-total impurity content / 100); Among them, K1 is the actual molecular ratio of electrolytic cell; Total impurity content is the total content of CaF2, KF, MgF2, LiF, AL2O3, NaO in electrolyte; (5) Calculate the calibration coefficient According to the theoretical discharge amount of single-cell aluminum fluoride constant feeder and the weighing determination result of actual discharge amount of aluminum fluoride constant feeder, the calibration coefficient is calculated, calibration coefficient = single-cell aluminum fluoride theoretical discharge amount / single-cell aluminum fluoride actual discharge amount; (6) Calculate the neutralization amount of aluminum fluoride required for the change of sodium content in series alumina and balanced alumina a. Sodium content in series alumina = (input alumina amount × sodium content in alumina) / total input amount; b. The neutralization amount of aluminum fluoride required for the change of sodium content in balanced alumina = (actual sodium content in alumina - average sodium content) × daily alumina discharge amount × ALF3 molecular weight / 2.4 / NaF molecular weight / 100; (7) Calculate the parameter modification value of electrolytic cell client Parameter modification value of electrolytic cell client = daily addition amount of aluminum fluoride × calibration coefficient; The daily addition amount of the aluminum fluoride = the single-cell maintenance amount of the electrolytic cell + the theoretical daily adjustment amount of the aluminum fluoride + the neutralization amount of the aluminum fluoride required for balancing the sodium content change in the alumina; The addition amount of the aluminum fluoride is the parameter modification value of the client end of the electrolytic cell.

2. A method of calculating the amount of aluminium fluoride to be added to an aluminium electrolysis cell as claimed in claim 1, c h a r a c t e r i s e d in that: When the under-over ratio changes, the addition amount of the aluminum fluoride is corrected, and the addition amount of the aluminum fluoride is increased or decreased by 2 kg when the under-over ratio is increased or decreased by 0.

01.

3. A method of calculating the amount of aluminium fluoride to be added to an aluminium electrolysis cell as claimed in claim 1, c h a r a c t e r i s e d in that: When the electrolyte temperature changes, the addition amount of the aluminum fluoride is corrected, and the addition amount of the aluminum fluoride is increased or decreased by 2 kg when the electrolyte temperature is increased or decreased by 2℃ within a range of 5℃.

4. A method of calculating the amount of aluminium fluoride to be added to an aluminium electrolysis cell as claimed in claim 1, c h a r a c t e r i s e d in that: When the needle vibration of the electrolytic cell changes, the addition amount of the aluminum fluoride is corrected, and the addition amount of the aluminum fluoride is decreased by 2 kg when the needle vibration value of the electrolytic cell is 5-10 mv, the addition amount of the aluminum fluoride is decreased by 10 kg when the needle vibration value of the electrolytic cell is 10-20 mv, and the addition amount of the aluminum fluoride is halved when the needle vibration value of the electrolytic cell is more than 20 mv.

5. A method of calculating the amount of aluminium fluoride to be added to an aluminium electrolytic cell as claimed in claim 1, characterised in that: When the swing of the electrolytic cell changes, the addition amount of the aluminum fluoride is corrected, and the addition amount of the aluminum fluoride is decreased by 2 kg when the swing value of the electrolytic cell is 2-5 mv, the addition amount of the aluminum fluoride is decreased by 10 kg when the swing value of the electrolytic cell is 6-10 mv, and the addition amount of the aluminum fluoride is halved when the swing value of the electrolytic cell is more than 10 mv.

Images