Cathode protection method for aluminum electrolysis cell

Abstract

The invention discloses a cathode protection method for an aluminum electrolysis cell, which solves the problem of serious non-uniform abrasion of a cathode caused by physical abrasion and electrochemical corrosion of the aluminum electrolysis cell, and adopts the technical scheme of implementing integral protection on a cathode abrasion area. The cathode protection frame is arranged above the cathode abrasion area, the filling material is arranged in the cathode protection frame, the flow speed of molten aluminum in the cathode abrasion area is reduced by means of the flow choking characteristic of the cathode protection frame, a material sediment accumulation protection layer is formed above the cathode abrasion area, a cathode is protected against erosion abrasion of the molten aluminum, and the service life of the cathode is prolonged. And the current density, the temperature and the aluminum carbide generation speed of a cathode abrasion area are reduced, the cathode abrasion deepening process is delayed, and the purposes of prolonging the safe operation life of the electrolytic cell and reducing the solid waste discharge amount are achieved.

Description

Technical Field

[0001] This invention relates to the field of cathode protection technology for aluminum electrolytic cells, specifically to a cathode protection method for aluminum electrolytic cells. Background Technology

[0002] The electrolytic aluminum industry is a key industry for carbon neutrality control. In recent years, the country has vigorously promoted energy-saving and carbon-reduction transformation in the electrolytic aluminum industry, promoted the large-scale development of aluminum electrolytic cells, and promoted the application of technologies such as graphitized cathodes. Regarding the large-scale development of aluminum electrolytic cells, 400KA and 500KA large electrolytic cells have become the mainstream cell type, and the proportion of electrolytic cells with a capacity of 600KA and above is also steadily increasing. However, large aluminum electrolytic cells have problems such as high local cathode current density and high local aluminum liquid flow rate. Therefore, the physical wear and electrochemical corrosion rate of the cathodes in large aluminum electrolytic cells are both relatively fast. In particular, the rapid flow of aluminum liquid causes severe erosion wear on the cathode surface, and the high cathode current density accelerates the electrochemical corrosion process, ultimately leading to cathode damage in large aluminum electrolytic cells after about 4 years. Especially in order to further reduce electrolysis energy consumption, electrolytic aluminum companies have begun to widely use graphitized cathodes. However, due to the non-wear-resistant nature of graphitized cathodes, the cathode corrosion problem is even more serious.

[0003] Analysis of the cathode erosion characteristics of large aluminum electrolytic cells in recent years revealed a correlation between severely eroded cathode areas and high-flow-rate regions within the cells. Over 90% of the severely eroded areas were located in regions with high aluminum melt flow velocities. Reny et al. observed the cross-section of cathode erosion in aluminum electrolytic cells and found that the eroded cathode profile exhibited a W-shaped curve, and this non-uniform erosion was particularly pronounced in large-scale, high-current-intensity aluminum electrolytic cells. Gao Bingliang et al., after observing the damage in a 600KA electrolytic cell on-site, found that damage typically occurred on the inlet side, while damage was less frequent on the outlet side. This is clearly related to the high aluminum melt flow rate, low sediment coverage, and high current density in the localized area on the inlet side. According to literature, the average erosion rate of graphitized cathodes is approximately 2.4 cm / a per year. In the early stage of operation of aluminum electrolysis cells (within 1500 days of cell age), the main wear is physical wear caused by the aluminum liquid scouring the cathode surface. The cathode erosion rate is relatively slow. When the cathode erosion depth reaches more than 10cm, the current density in the cathode erosion zone increases significantly, the formation rate of aluminum carbide accelerates, and the cathode erosion will be mainly electrochemical corrosion. Under the combined effect of local cathode high temperature, high current density, and high aluminum liquid flow rate, the rate of aluminum carbide formation and removal is accelerated, and the cathode erosion rate increases rapidly. The erosion depth often increases from 15cm to 25cm and then melts the cathode steel rod in less than a year.

[0004] Faced with the severe problem of cathode erosion in large aluminum electrolytic cells, electrolytic aluminum enterprises currently lack effective solutions. Often, workers are instructed to use iron tools to probe the cathode during electrode replacement. When areas with erosion exceeding 15cm are found, repair materials such as magnesia, magnesia bricks, calcium fluoride, crust blocks, and corundum are used for filling. Examples include CN113755896A, a method for repairing localized damage to cathode carbon blocks in aluminum electrolytic cells, and CN111690951A, a method for repairing cathode damage in aluminum electrolytic cells. However, due to the rapid flow of molten aluminum at the eroded cathode areas, the flowing molten aluminum carries away the repair material, resulting in a repair effect that typically lasts less than two months. Furthermore, the large furnace bottom area of ​​large aluminum electrolytic cells means that once deep cathode erosion occurs, multiple large-area deep erosion sites often exist simultaneously, making the investigation and repair of eroded cathode sites extremely difficult. Ultimately, just as one corrosion point is repaired, the repair material for another corrosion point is washed away. This cycle repeats itself, greatly increasing the labor intensity of workers in cathode repair and maintenance. At the same time, the lifespan of the electrolytic cell is not substantially improved. Furthermore, accidents such as aluminum rolling and cell leakage caused by unsatisfactory repair results have seriously threatened the safe production of aluminum electrolytic plants.

[0005] Large aluminum electrolytic cells suffer from non-uniform cathode erosion, and the eroded areas are characterized by high current density, localized high cathode temperature, and high aluminum melt flow velocity, further accelerating the formation of aluminum carbide on the cathode surface. This repetitive process of aluminum carbide formation and removal causes continuous erosion of the cathode. The existing point-repair method, which involves manually locating and repairing damaged points, can no longer meet the safety maintenance needs of large aluminum electrolytic cells. Therefore, there is an urgent need to develop a technical solution that can slow down the cathode erosion process, effectively improve the safe operating life of aluminum electrolytic cells, and reduce the labor intensity of workers in cathode repair and maintenance. This is of great significance to the safe production of aluminum electrolytic plants. Summary of the Invention

[0006] The purpose of this invention is to provide a cathodic protection method for aluminum electrolytic cells, addressing the severe problem of non-uniform cathode erosion in large aluminum electrolytic cells caused by the combined effects of physical wear and electrochemical corrosion, as mentioned in the background art. The rate of physical wear of the aluminum electrolytic cell cathode is related to the aluminum melt flow rate, while the rate of electrochemical corrosion is related to the cathode current density. Therefore, the core technical problems this invention aims to solve are: first, the high aluminum melt flow rate in the cathode erosion zone leads to rapid physical wear; second, the high current density in the cathode erosion zone leads to rapid electrochemical corrosion; third, non-uniform cathode erosion results in uneven cathode current distribution, increased horizontal current, and decreased electrolytic cell stability; fourth, existing repair and maintenance methods suffer from the problem that repair materials are carried away by the flowing aluminum melt, resulting in a short repair duration; fifth, large aluminum electrolytic cells have a large furnace bottom area, and existing point repair methods make it difficult to accurately locate erosion damage points manually, ultimately leading to unsatisfactory repair results and no substantial extension of the electrolytic cell's lifespan.

[0007] Research and analysis revealed that the cathode erosion zone in aluminum electrolytic cells is mainly distributed in areas with high aluminum liquid flow rates, while areas with low flow rates are easily covered by sediment. The current density in sediment-covered areas is low, resulting in a lower cathode erosion rate. Therefore, based on the distribution characteristics of cathode erosion zones in large aluminum electrolytic cells, the existing point-repair model is changed to a new maintenance model that implements overall protection of the cathode erosion zone. By adopting technical measures to reduce the aluminum liquid flow rate in the cathode erosion zone, a stable material sedimentation protective layer is formed above the cathode erosion zone, preventing direct scouring and wear of the cathode surface by the aluminum liquid. Simultaneously, since the conductivity of the soft sediment at the furnace bottom is approximately 1.0 S / cm, which is 50% of that of liquid electrolyte, the material sedimentation protective layer formed above the cathode erosion zone can increase the resistance of the cathode erosion zone, reduce the current density, local cathode temperature, and the rate of aluminum carbide formation on the cathode surface, thus slowing down the cathode erosion process and improving the safe operating life of the electrolytic cell.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for cathodic protection of an aluminum electrolytic cell, comprising an aluminum electrolytic cell cathode and a cathode erosion zone, wherein a repair material is disposed within the cathode erosion zone of the aluminum electrolytic cell, a cathode protection frame is disposed above the cathode erosion zone of the aluminum electrolytic cell, and a filler material is disposed within the cathode protection frame, wherein the particle density of the repair material is greater than the density of the molten aluminum, the volume density of the cathode protection frame is greater than the density of the molten aluminum, and the particle density of the filler material is greater than the density of the molten aluminum.

[0009] The cathode erosion zone is the cathode area in the aluminum electrolysis cell with a wear depth greater than 20 mm, including the cathode erosion trench area, the cathode erosion pit area, and the cathode crack area.

[0010] Preferably, the cathode protection frame is made of alumina-based material, magnesium oxide-based material, or silicon carbide-based material, with a bulk density of not less than 3000 kg / m³.

[0011] Preferably, the length of the cathode protection frame is 500mm to 2500mm, the width is 500mm to 1800mm, and the height is 50mm to 180mm.

[0012] Preferably, the cathode protection frame is assembled from multiple frame pieces with dovetail joints. The frame pieces are 150mm–1200mm long, 80mm–200mm wide, and 50mm–180mm high. The dovetail joints are 30mm–70mm wide and 20mm–60mm deep, with the height equal to the frame height. A 1mm–5mm expansion gap is left between the tenon and mortise in the dovetail joint to prevent thermal stress fracture of the cathode protection frame. Because the cathode surface of the aluminum electrolysis cell is uneven, the multi-frame assembly structure of the cathode protection frame helps to better fit the cathode protection frame to the cathode surface.

[0013] The temperature of the molten aluminum in the aluminum electrolysis cell is around 950℃, the height of the molten aluminum is 200mm~300mm, and the dynamic viscosity of the molten aluminum is 0.65×10. -3 The viscosity of molten aluminum is close to that of water at 40°C, and the fluid exhibits characteristics of shallow water. This can be determined using the Schamov formula: v = 1.14[gd(ρ...]. s -ρ) / ρ] 1 / 2 (h / d) 1 / 6 Verify the stability of the cathodic protection frame in molten aluminum. In the formula, v is the starting flow velocity (the critical average flow velocity at which particles transition from a static state to motion), and g is the acceleration due to gravity, taken as 9.8 m / s². 2 d represents the particle size, calculated based on the minimum size (frame height 0.05m) according to the cathodic protection frame size range. ρ s The density of the cathodic protection frame is set at 3000 kg / m³. 3 ρ is the density of molten aluminum, taken as 2300 kg / m³. 3 If h is the height of the molten aluminum and is taken as 0.26m, then the starting flow velocity of the 50mm particle in the molten aluminum is v = 0.579m / s. The actual size of the cathode protection frame is much larger than the 50mm particle, and the actual starting flow velocity is also much greater than 0.579m / s. However, the maximum flow velocity of the molten aluminum in a large aluminum electrolysis cell is generally no greater than 0.20m / s, and the average flow velocity of the molten aluminum is 0.08~0.10m / s. Therefore, the cathode protection frame is stable in position within the electrolysis cell.

[0014] Assuming the cathode protection frame is in a stable position, all viscous fluids, during movement, transfer momentum with the object in relative motion, generating a reaction force that hinders flow. Therefore, by placing a cathode protection frame above the cathode erosion zone, the flow resistance of the molten aluminum is increased, and the flow velocity of the molten aluminum is reduced. This helps to solve the problem of rapid physical wear caused by the high flow velocity of the molten aluminum in the cathode erosion zone, and also creates conditions for the formation of a stable material deposit protective layer above the cathode erosion zone.

[0015] Preferably, the repair material fills the cathode abrasion zone to a height not exceeding 50 mm above the cathode surface of the aluminum electrolytic cell.

[0016] Preferably, the repair material is made of fused white corundum, magnesia, magnesia bricks, magnesium fluoride, calcium fluoride, crust blocks, etc., with a particle density >3000 kg / m³.

[0017] Preferably, the particle size of the repair material is 1mm to 80mm.

[0018] Repair materials with a density greater than that of molten aluminum can squeeze out the space of molten aluminum in the cathode corrosion zone, preventing the flowing molten aluminum from directly scouring and wearing the cathode surface in the cathode corrosion zone. At the same time, it increases the resistance of the cathode corrosion zone, reduces the current density and local cathode temperature in this area, and slows down the electrochemical corrosion rate of the cathode.

[0019] Preferably, the filling thickness of the filler in the cathode protection frame is 20mm to 150mm. By adjusting the thickness of the filler in the cathode protection frame, the thickness of the material deposit protective layer formed above the cathode abrasion zone can be adjusted, thereby adjusting the cathode current distribution.

[0020] Preferably, the filler material is fused white corundum, magnesia, magnesia brick, etc., with a particle density >3000 kg / m³.

[0021] Preferably, the particle size of the filler is 3mm to 100mm, wherein particles with a particle size ≥8mm account for not less than 50% by weight percentage.

[0022] Preferably, to prevent the filler from being washed away by the flowing molten aluminum, the particle size of the uppermost layer of the filler is not less than 8 mm, and the filling thickness of the particles with a particle size of not less than 8 mm in the uppermost layer is not less than 10 mm.

[0023] In actual production, electrolytic aluminum enterprises often use repair materials with a particle size of 3mm to 5mm to fill the damaged areas without immediately being washed away by the molten aluminum. However, the repair effect generally lasts for less than 2 months. Therefore, this invention preferably uses filler material with a particle size of not less than 8mm for the top layer. According to the Szamov formula, the density of 8mm particle size is 3000 kg / m³. 3The starting flow velocity of the particles in the molten aluminum at a height of 260 mm is v = 0.315 m / s, while the maximum flow velocity of the molten aluminum is generally no greater than 0.20 m / s, which is less than the starting flow velocity of the 8 mm particle size. Therefore, even without considering the flow obstruction effect of the cathode protection frame, when the particle size of the top layer of filler is not less than 8 mm, the top layer of filler will not be washed away by the flowing molten aluminum.

[0024] The top layer of filler uses particles with a size of no less than 8mm. This ensures that the particles themselves are not washed away by the molten aluminum, and also protects the lower filler material from being carried away by the flowing aluminum, ensuring long-term stable material accumulation above the cathode corrosion zone. This effectively solves the problem of existing repair and maintenance methods where the repair material is carried away by the flowing aluminum, resulting in a short repair duration.

[0025] Positive and Beneficial Effects: This invention provides a cathodic protection method for aluminum electrolytic cells. By placing repair material within the cathode erosion zone of the aluminum electrolytic cell, setting a cathode protection frame above the erosion zone, and placing filler material within the cathode protection frame, the flow-blocking characteristics of the cathode protection frame reduce the flow velocity of the molten aluminum in the cathode erosion zone. This achieves the formation of a stable material sedimentation and accumulation protective layer above the cathode erosion zone, preventing direct erosion and wear of the cathode surface by the molten aluminum. Furthermore, the material sedimentation and accumulation protective layer can alter the cathode current distribution, reducing the current density, local cathode temperature, and the rate of aluminum carbide formation on the cathode surface in the cathode erosion zone, thus slowing down the cathode erosion process and achieving the goals of extending the safe operating life of the electrolytic cell and reducing the amount of solid waste discharged from the electrolytic cell. Simultaneously, this invention adopts a novel maintenance mode that provides overall protection for the cathode erosion zone, effectively solving the problems of difficulty in manually identifying eroded and damaged areas, high labor intensity for workers, and short duration of repair effects. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the distribution of the cathode erosion zone (W-shaped erosion trench) in Example 1;

[0027] Figure 2 This is a plan view of the cathode protection method for the aluminum electrolytic cell in Example 1;

[0028] Figure 3 This is a cross-sectional view (AA) of the cathode protection method for aluminum electrolytic cells in Example 1.

[0029] Figure 4 This is a three-dimensional diagram of the cathode protection method for aluminum electrolytic cells in Example 1;

[0030] Figure 5 This is a schematic diagram of the distribution of the cathode erosion zone (cathode crack) in Example 2;

[0031] Figure 6 This is a plan view of the cathode protection method for the aluminum electrolytic cell in Example 2;

[0032] Figure 7 This is a cross-sectional view (AA) of the cathode protection method for aluminum electrolytic cells in Example 2.

[0033] Figure 8 This is a three-dimensional diagram of the cathode protection method for aluminum electrolytic cells in Example 2;

[0034] Figure 9 This is a schematic diagram of the distribution of the cathode erosion area (erosion pit) and the cathode protection frame in Example 3;

[0035] Figure 10 This is a plan view of the cathodic protection method for the aluminum electrolytic cell in Example 3;

[0036] Figure 11 This is a cross-sectional view (AA) of the cathode protection method for aluminum electrolytic cells in Example 3.

[0037] Figure 12 This is a three-dimensional diagram of the cathode protection method for aluminum electrolytic cells in Example 3;

[0038] Figure 13 This is a schematic diagram of the cathodic erosion zone (depth < 10 cm) distribution in Example 4;

[0039] Figure 14 This is a plan view of the cathodic protection method for the aluminum electrolytic cell in Example 4;

[0040] Figure 15 This is a cross-sectional view (AA) of the cathode protection method for aluminum electrolytic cells in Example 4.

[0041] Figure 16 This is a three-dimensional diagram of the cathode protection method for aluminum electrolytic cells in Example 4;

[0042] Figure 17 This is a structural diagram of a cathode protection frame (rectangular).

[0043] Figure 18 This is a structural diagram of a hexagonal cathode protection frame.

[0044] Figure 19 This is a structural diagram of a cathode protection frame (square).

[0045] In the figure, 1 is the cathode of the aluminum electrolytic cell, 2 is the cathode abrasion zone, 3 is the repair material, 4 is the cathode protection frame, and 5 is the filler material. Detailed Implementation

[0046] The invention will now be further described with reference to the accompanying drawings:

[0047] A method for cathodic protection of an aluminum electrolytic cell includes an aluminum electrolytic cell cathode 1 and a cathode abrasion zone 2, characterized in that: a repair material 3 is provided in the cathode abrasion zone 2 of the aluminum electrolytic cell, a cathode protection frame 4 is provided above the cathode abrasion zone 2 of the aluminum electrolytic cell, and a filler material 5 is provided in the cathode protection frame 4, wherein the particle density of the repair material 3 is greater than the density of the molten aluminum, the volume density of the cathode protection frame 4 is greater than the density of the molten aluminum, and the particle density of the filler material 5 is greater than the density of the molten aluminum.

[0048] Example 1

[0049] like Figure 1 , Figure 2 , Figure 3 , Figure 4 As shown, this embodiment is mainly applied to the cathode protection of aluminum electrolytic cells with a cell age of more than 1200 days, a cathode erosion width of 500mm to 800mm, a depth of more than 100mm, and a cathode surface forming a W-shaped erosion trench. The cathode erosion area 2 is a W-shaped cathode erosion trench area.

[0050] The cathode protection frame 4 is made of alumina-based material, which is obtained by vibration molding and sintering, and has a bulk density of >3100 kg / m³.

[0051] like Figure 2 , Figure 3 , Figure 4 , Figure 17 As shown, the cathode protection frame 4 is rectangular, with a length of 1500mm, a width of 750mm, and a height of 85mm.

[0052] like Figure 2 , Figure 3 , Figure 4 , Figure 17 As shown, the cathode protection frame 4 is assembled from multiple frame pieces with dovetail tenon structures. The frame pieces are 400mm to 700mm long, 110mm to 180mm wide, and 85mm high. The dovetail tenon structures are 50mm to 70mm wide and 30mm to 50mm deep. The height of the dovetail tenon structure is equal to the height of the frame piece. The gap between the tenon and the mortise in the dovetail tenon structure is 2mm to 4mm.

[0053] The stability of the cathode protection frame 4 was further verified based on fluid thrust and friction: According to the fluid thrust formula: F=ρ×v²×A, where ρ is the density of the molten aluminum, taken as 2300Kg / m³. 3v is the flow velocity of the molten aluminum. Since the flow velocity of molten aluminum is generally no greater than 0.20 m / s, we take the maximum flow velocity of 0.2 m / s. A is the area of ​​the object impacted by the fluid. Here, we take the longest side of the cathodic protection frame 4, 1.5 m and the height of 0.085 m, as the force-bearing surface for calculation. Therefore, the maximum thrust of the molten aluminum on the cathodic protection frame 4 is Fmax = 2300 × 0.22 × 1.5 × 0.085 = 11.7 N. The cathodic protection frame 4 is mainly stabilized on the cathode surface by friction. The formula for calculating friction is f = μN, where μ represents the coefficient of friction and N represents the normal force. Since the coefficient of friction of graphite is usually between 0.05 and 0.44, we calculate based on the minimum value μ = 0.05. The width of the frame of the cathodic protection frame 4 is calculated as 130 mm, and the volume of the cathodic protection frame 4 is 0.044 m³. 3 The minimum frictional force between the cathode protection frame 4 and the cathode. fmin = 0.05 × (3100 - 2300) × 0.044 × 9.8 = 17 N. Since fmin > Fmax, the cathode protection frame 4 is stable on the cathode surface and can effectively block the flow of molten aluminum and reduce its velocity. Actual stability tests of the cathode protection frame 4 were conducted in a 400KA aluminum electrolysis cell. After the cathode protection frame 4 was placed in the high-velocity region of the electrolysis cell, it was very difficult to manually move it using iron tools, indicating that the bonding force between the cathode protection frame 4 and the cathode surface is much greater than the frictional force calculated based on a friction coefficient of 0.05.

[0054] like Figure 3 As shown, the height of the repair material 3 after filling the cathode abrasion zone 2 is no more than 50 mm above the surface of the aluminum electrolytic cell cathode 1.

[0055] The repair material 3 is made of fused white corundum, magnesia, and magnesia brick, with a particle density >3100 kg / m³.

[0056] The repair material 3 has a particle size of 3mm to 50mm, and by weight percentage: 20% to 30% for particles of 3 to 5mm, 20% to 30% for particles of 8 to 12mm, and 40% to 60% for particles of 25mm to 50mm.

[0057] like Figure 3 As shown, the filling thickness of the filler 5 within the cathode protection frame 4 is 30mm to 80mm.

[0058] The filler 5 is made of fused white corundum and magnesia, with a particle density >3400 kg / m³. The fused white corundum constitutes no less than 80% of the filler 5 by weight.

[0059] The filler 5 has a particle size of 3mm to 50mm, and by weight percentage: 5% to 10% for particles of 3-5mm, 10% to 20% for particles of 8-12mm, and 70% to 85% for particles of 25mm to 50mm.

[0060] like Figure 2 , Figure 3 , Figure 4 As shown, the particle size of the uppermost layer of the filler 5 is not less than 20 mm, and the filling thickness of the particles with a particle size of not less than 20 mm is not less than 25 mm.

[0061] Installation steps: When changing electrodes in the aluminum electrolytic cell, after pulling out the anode, fill the repair material 3 into the cathode erosion area 2 and level it. After leveling, the anode can be used to compact the repair material 3. The filling height of the repair material 3 should not be higher than 50mm above the surface of the cathode 1 of the aluminum electrolytic cell. After cleaning up the material blocks that fell into the cell during electrode changing, use an overhead crane to lift the cathode protection frame 4 and place it above the cathode erosion area 2. Then, place the filler material 5 into the cathode protection frame 4. Alternatively, the filler material 5 can be pre-laid in the cathode protection frame 4 before using an overhead crane to lift and place it above the cathode erosion area 2. After the overall installation is completed, as shown in the figure. Figure 2 , Figure 4 As shown.

[0062] Implementation Results: This embodiment adopts a technical solution for overall protection of the W-shaped cathode erosion trench area, solving the problems of difficulty in finding damaged points and unsatisfactory repair effects in the original point repair mode. At the same time, the material sedimentation and accumulation protective layer formed above the cathode erosion zone 2 can reduce the current density of the cathode erosion zone 2, slow down the erosion process of the cathode erosion zone 2, and achieve the purpose of extending the safe operating life of the aluminum electrolytic cell and reducing solid waste emissions. In addition, in this embodiment, the cathode erosion zone 2 is close to the side area of ​​the electrolytic cell. According to the obstruction acceleration phenomenon of fluid, the aluminum liquid flow rate in the side area of ​​the electrolytic cell decreases under the obstruction of the cathode protection frame 4, while the aluminum liquid flow rate in the middle area increases. This flow characteristic not only helps to form a stable material sedimentation and accumulation protective layer above the cathode erosion zone 2, reducing the current concentration in the side area of ​​the electrolytic cell, but also reduces sedimentation in the middle area, enhances the conductivity of the middle area, and ultimately achieves the purpose of improving the cathode current distribution and promoting the formation of the side furnace wall.

[0063] Example 2

[0064] The difference between this embodiment and Embodiment 1 is that:

[0065] like Figure 5 , Figure 6 , Figure 7 , Figure 8 As shown, this embodiment is mainly applied to the cathode protection of aluminum electrolytic cells with cathode cracks, and the cathode erosion zone 2 is the cathode crack area.

[0066] like Figure 6 , Figure 7 , Figure 8 , Figure 17 As shown, the cathode protection frame 4 is rectangular, with a length of 1500mm, a width of 650mm, and a height of 85mm. Because the crack area is elongated and narrow, and the crack width generally does not exceed 200mm, the width of the cathode protection frame 4 is reduced to 650mm.

[0067] The stability of the cathode protection frame 4 was further verified based on fluid thrust and friction: the maximum thrust of the molten aluminum acting on the cathode protection frame 4, Fmax, is 2300 × 0.22 × 1.5 × 0.085 = 11.7 N. Assuming a frame width of 130 mm, the volume of the cathode protection frame 4 is 0.042 m³. 3 The minimum frictional force between the cathode protection frame 4 and the cathode is fmin = 0.05 × (3100 - 2300) × 0.042 × 9.8 = 16.4 N. Since fmin > Fmax, the cathode protection frame 4 is stable on the cathode surface.

[0068] The repair material 3 is made of fused white corundum with a particle density >3500 kg / m³.

[0069] like Figure 7 As shown, the height of the repair material 3 after filling the cathode abrasion zone 2 is no more than 30 mm above the surface of the aluminum electrolytic cell cathode 1.

[0070] Because large-particle repair materials are not conducive to filling cracks, the particle size of the repair material 3 is 3mm to 12mm, and the weight percentage is as follows: 30% to 40% for particles of 3 to 5mm, 30% to 40% for particles of 5 to 8mm, and 20% to 40% for particles of 8mm to 12mm.

[0071] like Figure 7 As shown, the filling thickness of the filler 5 within the cathode protection frame 4 is 30mm to 50mm.

[0072] The filler 5 has a particle size of 8mm to 50mm, and by weight percentage: 8mm to 12mm particles account for 10% to 30%, and 25mm to 50mm particles account for 70% to 90%.

[0073] like Figure 6 , Figure 7 , Figure 8 As shown, the top layer of the filler 5 has a particle size of not less than 20 mm, and the filling thickness of the top layer of particles with a particle size of not less than 20 mm is not less than 25 mm.

[0074] Installation steps: When changing electrodes in the aluminum electrolytic cell, after pulling out the anode, fill the cathode erosion area 2 with repair material 3 and tamp it down tightly with an iron rod. The filling height of repair material 3 should not exceed 30mm above the surface of the cathode 1 of the aluminum electrolytic cell. After cleaning up any material blocks that fell into the cell during electrode replacement, use an overhead crane to lift and place the cathode protection frame 4 above the cathode erosion area 2. Then, place the filler material 5 into the cathode protection frame 4. Alternatively, the filler material 5 can be pre-laid inside the cathode protection frame 4 before being lifted and placed above the cathode erosion area 2 by an overhead crane. After the overall installation is completed, proceed as follows: Figure 6 , Figure 8 As shown.

[0075] Implementation Results: The technical solution adopted in this embodiment for the cathode crack area solves the problem of unsatisfactory repair effects of the original repair mode. At the same time, by reducing the flow rate, a stable material sedimentation and accumulation protective layer is formed in the cathode crack area, which can protect the repair material 3 in the crack from being carried away by the flowing aluminum liquid. In addition, the material sedimentation and accumulation protective layer can also reduce the current density in the area surrounding the cathode erosion zone 2, thereby cooling the furnace bottom in the area surrounding the cathode erosion zone 2. This is more conducive to the filling and solidification of sediment, achieving the purpose of long-term protection of the cathode crack area.

[0076] Example 3

[0077] The difference between this embodiment and Embodiment 1 is that:

[0078] like Figure 9 , Figure 10 , Figure 11 , Figure 12 As shown, this embodiment is mainly applied to the cathode protection of aluminum electrolytic cells with corrosion pits having a cathode depth exceeding 15cm. The cathode corrosion zone 2 is the cathode corrosion pit area.

[0079] like Figure 10 , Figure 11 , Figure 12 , Figure 18 , Figure 19 As shown, the height of the cathode protection frame 4 is 120mm. A hexagonal cathode protection frame 4 is laid above the cathode erosion area 2 with a pit diameter ≥ 300mm. The distance between opposite sides of the hexagon is 1150mm. A square cathode protection frame 4 is laid above the cathode erosion area 2 with a pit diameter < 300mm. The side length of the square is 700mm.

[0080] like Figure 18As shown, the hexagonal cathode protection frame 4 is assembled from multiple frame pieces with dovetail tenon structures. The frame pieces are 500mm to 700mm long, 110mm to 150mm wide, and 120mm high. The dovetail tenon structures are 50mm to 70mm wide and 30mm to 50mm deep. The height of the dovetail tenon structure is equal to the height of the frame pieces. The gap between the tenon and the mortise in the dovetail tenon structure is 2mm to 4mm.

[0081] like Figure 19 As shown, the square cathode protection frame 4 is assembled from multiple frame pieces with dovetail tenon structures. The frame pieces are 500mm to 600mm long, 110mm to 150mm wide, and 85mm high. The dovetail tenon structures are 50mm to 70mm wide and 30mm to 50mm deep. The height of the dovetail tenon structures is equal to the height of the frame pieces. The gap between the tenon and the mortise in the dovetail tenon structure is 2mm to 4mm.

[0082] The stability of the hexagonal cathodic protection frame 4 was further verified based on fluid thrust and friction: the maximum thrust of the molten aluminum acting on the cathodic protection frame 4, Fmax, is 2300 × 0.22 × 1.15 × 0.12 = 12.7 N. Based on the hexagonal side-to-side distance of 1150 mm, frame width of 130 mm, and height of 120 mm, the volume of the cathodic protection frame 4 is calculated to be 0.055 m³. 3 Therefore, the minimum frictional force between the cathode protection frame 4 and the cathode is fmin = 0.05 × (3100 - 2300). ×0.055×9.8=21.6N. Since fmin>Fmax, the position of the cathode protection frame 4 is stable.

[0083] The stability of the square cathodic protection frame 4 was further verified based on fluid thrust and friction: the maximum thrust of the molten aluminum acting on the cathodic protection frame 4, Fmax, is 2300 × 0.22 × 0.7 × 0.12 = 7.7 N. Based on the square's side length of 700 mm, frame width of 130 mm, and height of 85 mm, the volume of the cathodic protection frame 4 is calculated to be 0.03 m³. 3 The minimum frictional force between the cathode protection frame 4 and the cathode is fmin = 0.05 × (3100 - 2300) × 0.03 × 9.8 = 12 N. Since fmin > Fmax, the position of the cathode protection frame 4 is stable.

[0084] The repair material 3 is made of fused white corundum, magnesia, and magnesia brick, with a particle density >3100 kg / m³.

[0085] The particle size of the repair material 3 is 3mm to 50mm.

[0086] For areas of cathodic abrasion zone 2 where the abrasion depth exceeds 15cm but the steel rod has not melted, large-particle repair material 3 is used for filling, with the following weight percentages: 20%–30% for particles of 3–5mm, 60%–70% for particles of 8–12mm, and 0%–20% for particles of 25mm–50mm.

[0087] The areas where the steel bars have been melted are mainly filled with small-particle repair material 3, with the following weight percentages: 3-5mm particles account for 45%-50%, 8-12mm particles account for 45%-50%, and 25mm-50mm particles account for 0%-10%.

[0088] like Figure 10 , Figure 11 , Figure 12 As shown, the filling thickness of the filler 5 within the cathode protection frame 4 is 60mm to 120mm.

[0089] like Figure 10 , Figure 11 , Figure 12 As shown, the top layer of the filler 5 has a particle size of not less than 20 mm, and the filling thickness of the top layer of particles with a particle size of not less than 20 mm is not less than 25 mm.

[0090] Installation steps: Same as in Example 1. After installation, as follows: Figure 10 , Figure 12 As shown.

[0091] Implementation effect: The technical solution adopted in this embodiment for the abrasion pit area can form a stable material sedimentation and accumulation protective layer in the abrasion pit area, protecting the repair material in the abrasion pit from being carried away by the flowing aluminum liquid. At the same time, the material sedimentation and accumulation protective layer can also reduce the current density in the area around the abrasion pit, thereby cooling the furnace bottom in the area around the abrasion pit. This is conducive to the filling and solidification of sediment, achieving the purpose of long-term protection of the abrasion pit area.

[0092] Example 4

[0093] The difference between this embodiment and Embodiment 1 is that:

[0094] like Figure 13 , Figure 14 , Figure 15 , Figure 16 As shown, this embodiment is mainly applied to the cathodic protection of aluminum electrolytic cells with a cell age of less than 1500 days, a cathode erosion depth of less than 10cm, and no obvious damage found. The cathode erosion zone 2 is a region of high flow rate of molten aluminum with a cathode erosion depth of less than 10cm.

[0095] like Figure 14 , Figure 15 , Figure 16 , Figure 17As shown, the cathode protection frame 4 is rectangular, with a length of 1500mm, a width of 750mm, and a height of 85mm.

[0096] The repair material 3 is made of fused white corundum with a particle density >3500 kg / m³.

[0097] like Figure 15 As shown, the height of the repair material 3 after filling the cathode abrasion zone 2 is no higher than the surface of the aluminum electrolytic cell cathode 1.

[0098] The particle size of the repair material 3 is 8mm to 50mm.

[0099] Because the cathodic corrosion depth is relatively shallow, large-particle repair material 3 is laid in the cathodic corrosion zone 2, with the following weight percentages: 40% to 50% for particles with a size of 8 to 12 mm and 50% to 60% for particles with a size of 25 to 50 mm.

[0100] like Figure 15 As shown, the filling thickness of the filler 5 within the cathode protection frame 4 is 20mm to 50mm.

[0101] The filler 5 is made of fused white corundum with a particle density >3500 kg / m³.

[0102] The filler 5 has a particle size of 8mm to 50mm, and by weight percentage: 10% to 20% for particles of 8mm to 12mm and 80% to 90% for particles of 25mm to 50mm.

[0103] like Figure 14 , Figure 15 , Figure 16 As shown, the top layer of the filler 5 has a particle size of not less than 20 mm and a filling thickness of not less than 20 mm.

[0104] Installation steps: Due to the shallow depth of cathode erosion, the installation steps can be simplified. Repair material 3 and filler 5 are pre-laid inside the cathode protection frame 4 according to particle size and filling thickness. When the aluminum electrolysis cell is switched, an overhead crane is used to hoist the cathode protection frame 4, repair material 3, and filler 5 together and place them above the cathode erosion area 2. After the overall installation is completed, as shown... Figure 14 , Figure 16 As shown.

[0105] Implementation Results: The cathodic protection technology adopted in this embodiment for the high-velocity aluminum liquid region with a cathode erosion depth of less than 10cm can reduce the aluminum liquid flow velocity above the cathode erosion zone 2, achieving the formation of a stable material sedimentation and protective layer above the cathode erosion zone 2. This reduces the current density in the cathode erosion zone 2, slows down the erosion process, and effectively improves the problem of non-uniform erosion of the cathode carbon block. This achieves the goal of extending the service life of the aluminum electrolysis cell and reducing solid waste emissions. Simultaneously, it helps improve the cathode current distribution and enhance the operational stability of the electrolysis cell.

[0106] The above embodiments are some embodiments of the present invention and are only used to illustrate the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, etc., made by those skilled in the art without creative effort within the spirit and principles of the present invention should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for cathode protection of an aluminum electrolytic cell, comprising an aluminum electrolytic cell cathode (1) and a cathode erosion zone (2), characterized in that: Repair material (3) is provided in the cathode abrasion zone (2) of the aluminum electrolytic cell, a cathode protection frame (4) is provided above the cathode abrasion zone (2) of the aluminum electrolytic cell, and filler material (5) is provided in the cathode protection frame (4). The particle density of the repair material (3) is greater than that of the aluminum liquid, the volume density of the cathode protection frame (4) is greater than that of the aluminum liquid, and the particle density of the filler material (5) is greater than that of the aluminum liquid.

2. The method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The cathode protection frame (4) is made of alumina-based material, magnesium oxide-based material, or silicon carbide-based material.

3. The method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The repair material (3) is made of fused white corundum, magnesia sand, magnesia brick, magnesium fluoride, calcium fluoride, and crust block, and the filler material (5) is made of fused white corundum, magnesia sand, and magnesia brick.

4. The method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The length of the cathode protection frame (4) is 500mm to 2500mm, the width is 500mm to 1800mm, and the height is 50mm to 180mm.

5. The method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The cathode protection frame (4) is assembled from multiple frame pieces with dovetail tenon structure. The frame piece is 150mm to 1200mm long, 80mm to 200mm wide, and 50mm to 180mm high. The dovetail tenon structure is 30mm to 70mm wide and 20mm to 60mm deep. The height of the dovetail tenon structure is equal to the height of the frame piece. The gap between the tenon and the mortise in the dovetail tenon structure is 1mm to 5mm.

6. The method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The height of the repair material (3) after filling the cathode abrasion zone (2) is no more than 50 mm above the surface of the cathode (1) of the aluminum electrolytic cell.

7. The method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The particle size of the repair material (3) is 1mm to 80mm.

8. The method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The filling thickness of the filler (5) in the cathode protection frame (4) is 20mm to 150mm.

9. A method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The particle size of filler (5) is 3mm to 100mm.

10. A method for cathodic protection of an aluminum electrolytic cell according to claim 1, characterized in that: The particle size of the top layer of filler (5) is not less than 8mm.

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