Electrolytic aluminum raw anode cooling model building method and application thereof

Abstract

The invention discloses an electrolytic aluminum raw anode cooling model establishing method and application thereof, belongs to the technical field of electrolytic aluminum carbon production, and aims to solve the problems that in the prior art, research on the incidence relation between the strength of an anode carbon block and a cooling process is lacked, and related process control is blank. The method comprises the following steps: carrying out a green anode strength and temperature relation exploration experiment; calculating the minimum cooling thickness of the green anode; developing a green anode cooling model; green anode cooling influence factors are analyzed; and applying the model. According to the method, the extensive empirical operation mode of current raw anode cooling is fundamentally solved, the conventional cognition that the cooling process and forming are not linked is broken, the cooling process also participates in a production management and control system for anode quality improvement, positive significance is also achieved for production line transformation with tight plant space, and the method is worthy of popularization and application. And a large transformation space can be provided for long-distance chain plate conveying.

Description

Technical Field

[0001] This invention belongs to the field of electrolytic aluminum carbon production technology, specifically relating to a method for establishing a cooling model for the green anode of electrolytic aluminum and its application. Background Technology

[0002] In electrolytic aluminum production enterprises, carbon plants are often paired with anode carbon plants to produce anode carbon blocks for use as electrodes. After the raw anode carbon blocks are kneaded and shaped, they need to be cooled before being stacked, transported, and put into the calcination process. Current technologies for anode quality research focus primarily on strength, with little in-depth exploration of the relationship between anode carbon block strength and molding temperature, cooling time, and cooling temperature.

[0003] A survey was conducted on the green anode cooling process of major domestic anode manufacturers, resulting in numerous survey feedback records, including the green anode cooling process parameter list for Chalco Lanzhou Branch and Liancheng Branch shown in the table below: And the following table shows the list of raw anode cooling process parameters for Guangxi Pingguo Company and Huomei Hongjun Company: ; The survey results and table data clearly show that the mainstream cooling methods for green anodes in China are water bath and natural cooling. Freshly formed green anode carbon blocks (also known as green anodes, green blanks, or carbon blocks; the corresponding finished product after roasting is called anode carbon blocks, prebaked anodes, etc.) are directly fed into a cooling water tank via plate chains, overhead chains, or hanging frames. After a water bath of 30-150 minutes, they exit the water and enter the natural cooling stage on a plate conveyor. Because water bath cooling of green anodes is fast, it requires a large area, and the water bath cooling time and natural cooling time vary from company to company. Some companies, limited by the tank area or the configuration of the vibrating table, have a water bath time of about 30 minutes, while others have a time of more than two hours. Furthermore, the methods of water bath and natural cooling differ, all relying on traditional production experience to control the water bath cooling time, forming temperature, and water temperature, without a unified standard. There are significant differences in the current green anode cooling processes of various companies, and they are unaware of the key points to consider in the cooling process. Most importantly, almost all carbon plants have not paid attention to the relationship between green block quality problems (cracks) and the cooling process, believing that there is no correlation.

[0004] The mainstream green anode cooling process abroad is a combination of spray cooling and natural cooling, or purely natural cooling. After the green anode is vibrated and formed, compressed air is used to atomize softened water. The atomized water mist is sprayed onto the surface of the high-temperature green billet. Due to the small specific surface area of ​​the fine water mist particles, the forced convection heat transfer coefficient is large, and more heat is carried away, resulting in a better cooling effect. However, this cooling method is much more expensive than water bath cooling. Generally, the atomization distance of the green billet on the conveyor belt is relatively short, about 10-20 meters, and the remaining conveying distance is cooled naturally.

[0005] In our research on anode quality, we discovered that the strength of the anode carbon block, as an important quality indicator, is related to the molding temperature, cooling time, and cooling temperature. Therefore, exploring the specific correlation and finding a feasible green anode cooling model and applying it in production has become a technical problem that has troubled the R&D personnel of the carbon plant. Summary of the Invention

[0006] The purpose of this invention is to provide a method for establishing a cooling model for the green anode of electrolytic aluminum and its application, in order to solve the problem that there is a lack of research on the correlation between the strength of the anode carbon block and the cooling process in the existing technology, and the lack of related process control.

[0007] To solve the above problems, the technical solution of the present invention is as follows: A method for establishing a cooling model for the green anode of electrolytic aluminum, comprising the following steps: S1. Experiment exploring the relationship between the strength of the anode and temperature; Samples of the produced raw blocks were taken and their strength was tested. Meanwhile, backup samples were used to test the relationship between strength and temperature in the laboratory. The test results show a specific temperature T℃. After this specific temperature, the flexural strength will decrease significantly. The critical temperature point for the flexural strength of the green body is determined to be T℃. S2. Calculation of minimum cooling thickness for green anode; S2.1, Simulation of the stress on the raw anode stack; After being cooled in a water tank, the green anodes are naturally cooled by a conveyor chain. When the number of green blocks on the chain exceeds the number set when the production line was built, the stacking crane in the green block warehouse begins to clamp the carbon blocks. At this time, the green blocks will be subjected to external force generated by the clamps. The external force at this moment is simulated and calculated, and the conclusion is that the carbon blocks must be cooled to a certain temperature so that their strength is sufficient to resist the lifting force generated by the clamps and will not deform or crack. S2.2, Minimum cooling thickness t; According to S1, the critical temperature for flexural strength is 80℃. This means that if the temperature of the green block is higher than 80℃ during the cooling process, the compressive and flexural strength of the green block cannot resist the pre-tightening force of the clamp when the stacking crane clamp operates on it, and surface or internal cracks will appear in the carbon block. Only when the temperature of the green block is lower than 80℃ can the green block strength be high enough to resist the pre-tightening force of the clamp. However, after the carbon block is cooled by circulating water, the internal temperature distribution is uneven and there is a large temperature gradient. Therefore, it is necessary to calculate the minimum cooling thickness t that the carbon block can withstand the clamping force. That is, as long as the temperature of the carbon block in this thickness area is below 80℃, the carbon block will not deform or crack due to the external clamping force. At this point, further experiments are needed to collect temperature data from the center of the carbon block to its outer surface along the horizontal centerline after the carbon block has been water-cooled for 30 minutes, and to plot the temperature distribution curve along the centerline of the carbon block. The curve drawn can express the trend of the carbon block dissipating heat to the surroundings during the cooling process. The temperature of the carbon block gradually decreases from the center to the surface. When the temperature of the carbon block from a certain area in the center to the surface area is all below the critical temperature of flexural strength, the thickness of that area, that is, the distance from that point to the surface, is called the minimum cooling thickness t. S2.3 Calculation of minimum cooling thickness t; The force analysis of the clamps on the charcoal blocks during the stacking process by the overhead crane is as follows: From ∑Fx=0, we can deduce that the force on the carbon block is Fleft = Fright; ∑Fy=0 can be used to infer ; The minimum cooling thickness t can be calculated based on the flexural strength data of the carbon block: ; c9 is a coefficient; Based on the relationship between the strength and temperature curves of the green anode, it can be concluded that when the temperature in the outer region from the surface of the green anode to the center at a depth of t is lower than T℃, the carbon block cracking problem will not occur under the clamps of the stacking crane. S3, Development of a green anode cooling model; S3.1 Geometric Model and Mesh Generation; The calculation is performed using a two-dimensional model; The first developed geometric models were water-cooled and air-cooled; Next, mesh the two according to the geometric model; mesh control and mesh refinement operation of the carbon block area, set the mesh of the carbon block area to 1-2mm to facilitate monitoring the temperature distribution of the carbon block at any thickness; S3.2, Physical properties and boundary conditions; The physical properties of the green body, including specific heat and thermal conductivity, have a significant impact on the calculation results. These properties can be obtained by consulting literature and actual measurement data. (1) Specific heat of the anode: The specific heat is a function of temperature: ; Where T is the thermodynamic temperature, K; a=42.52094, b=3.18657, c=-0.00172, d=3.1×10 -7 ; (2) Thermal conductivity of the green anode: The thermal conductivity is a function of temperature. ; Where T is the thermodynamic temperature, K; A=-9.103, B=0.0569, C=-8.602×10 -5 D = 5.756 × 10 -8 E = -1.38 × 10 -11 ; S3.3 Simulation Calculation Results; (1) Water-cooling simulation results; After establishing the two-dimensional geometric model, meshing, and setting boundary conditions, the temperature distribution of the carbon block in the simulation can be plotted, focusing on different time points t. 水1 ...t 水n Does the temperature distribution along the width of the carbon block conform to the temperature distribution law of heat conduction and heat transfer? That is, the heat in the center of the carbon block is gradually transferred to the surrounding area through the cooling water, and the temperature shows a slow downward trend. The temperature in the center area is the highest, and the temperature around the carbon block shows a clear temperature gradient. If the temperature distribution diagram of the carbon block calculated by simulation conforms to the above-mentioned temperature distribution law of heat conduction and heat transfer, then the simulation calculation is usable; if it does not conform, it is necessary to check whether the physical property parameters of the green body are appropriate and make corrections until the temperature distribution diagram of the carbon block calculated by simulation conforms to the above-mentioned temperature distribution law of heat conduction and heat transfer. (2) Simulation results of air cooling; Because the air-cooling conditions vary greatly among production enterprises, this step is simplified based on the actual air-cooling model. The heat dissipation space is simplified to only consider the top 3m space of the conveyor chain; After simplification, the simulation results show the temperature change of the carbon block under the condition of water cooling followed by air cooling and natural heat dissipation: air cooling t 空n Minutes later, the average temperature began to drop, but the drop was limited. (3) Simulation calculation results of the green anode cooling process; Combining the results of water cooling and air cooling, the simulation calculation results of the green anode cooling process can be obtained, which represents the entire green anode cooling process, including water bath cooling in the water tank and natural air cooling process on the plate chain. The temperature at the minimum cooling thickness is defined as the point of concern. Its behavior throughout the cooling process is as follows: This point of concern temperature drops rapidly during water cooling, but after water exit, it gradually increases and then decreases during the air cooling stage. It is necessary to control the highest temperature T of the carbon block during the reheating stage of the point of concern after water exit. 空MAX ℃ is below the critical cooling temperature T℃; S4. Analysis of factors affecting the cooling of the green anode; S4.1 The effect of molding temperature; Focusing on the actual molding temperature of the raw anode carbon block and extending it, we calculate the temperature at the minimum cooling thickness t of the carbon block corresponding to the molding temperature range of 140℃ to 165℃. This is used to verify the simulation model and see if the influence of the molding temperature on the temperature of interest is basically positively linear. If it is linear, the model passes the verification. If it is not positively linear, we need to trace back and re-analyze the factors to model. S4.2, Water cooling time; There is a non-linear negative correlation between the water cooling time and the temperature of interest after green body forming. By testing different water cooling times and temperatures of interest, the influence curve of cooling time on the temperature of interest can be plotted. Based on this curve, the cooling time in the water tank can be dynamically adjusted to ensure that the water cooling time is shortened as much as possible without affecting the quality of the charcoal blocks. S4.3, Circulating cooling water temperature; In the green anode water cooling process, the circulating cooling water temperature is a very important parameter. This parameter changes with the seasons. The effect curve of cooling time on the temperature of the point of interest can be plotted by testing the circulating cooling water temperature and the temperature of the point of interest. The circulating cooling water temperature can be dynamically adjusted using this curve.

[0008] Furthermore, the simulation calculation in S2.1 uses the simulation module in SolidWorks, focusing on the relationship between the force causing the carbon block to deflect due to the static friction force on the surface generated by the pressure on both sides of the fixture and the flexural strength of the carbon block; the simulation calculation result of this relationship can be expressed as a simulated cloud diagram of the stress on the cross section of the raw block; When the green billet is subjected to the lifting force of the clamp, it will generate an upward resistance, which is actually a static friction force. The end face is the position where the lifting force is the greatest. Extrusion force is generated on the top surface of the green billet and tension force is generated on the bottom surface. The interaction between the two will produce deflection. Therefore, the carbon block must be cooled to a certain temperature so that its strength is sufficient to resist the lifting force generated by the clamp and will not deform or crack.

[0009] Furthermore, in the process of establishing the model in S3.1, the geometric model was appropriately simplified and made assumptions, mainly including: (1) The raw anode carbon bowl and the chamfered structure around it were ignored; (2) The flow of the medium in the circulating water tank is not considered, and the cooling medium is in a static state; (3) To reduce the amount of calculation, a symmetrical structure is set up, with the carbon block located in the center of the pool; (4) Ignoring the adjacent carbon blocks, the adjacent carbon blocks actually have an impact on heat transfer.

[0010] Furthermore, the derivation process of the temperature of the carbon block at the point of concern after effluent in S3.3 is as follows: Firstly, the temperature at this point drops rapidly during water cooling, primarily due to the temperature difference between the high-temperature carbon block and the low-temperature circulating cooling water, as well as the proximity to the carbon block surface. The temperature at this location drops from t... 水1 ...t 水n During the water cooling process over a period of time, the initial cooling temperature T0℃ of the green anode carbon block (the temperature at which it enters the water cooling process after molding) drops to around T℃, the critical temperature point for flexural strength. Secondly: After water discharge, the temperature at the point of interest during the air-cooling stage shows a trend of gradually increasing and then decreasing: the highest temperature of the reheating stage in this air-cooling stage is set as T. 空MAX ℃; The laboratory data on the strength and temperature of the anode carbon block obtained in S1 show that the critical temperature point for flexural strength is T℃, which is also called the critical cooling temperature, T℃. The time t is the intersection point between the temperature at the minimum cooling thickness t and the critical cooling temperature during the air cooling temperature rise process. 空1 The time t is the intersection point between the air-cooled temperature decrease and the critical cooling temperature. 空1 During the cooling time t 空1 -t 空2 During the process, the temperature of the minimum cooling thickness area exceeds the critical cooling temperature. According to the stress analysis, if the carbon blocks are stacked during this period, the strength of this area is insufficient to support the impact of the clamp, which may easily lead to internal cracks in the carbon blocks. However, the temperature of highest concern during air cooling is T. 空MAX ℃, exceeding the critical cooling temperature (T 空MAX -T)℃, therefore the water cooling time t needs to be strictly controlled. 水n This causes the highest temperature T of the charcoal block during the reheating stage after water discharge to be of concern. 空MAX ℃ is below the critical cooling temperature T℃.

[0011] An application of a method for establishing a green anode cooling model for electrolytic aluminum, characterized in that the above method is applied to a 500kA green anode cooling process; The specific application of the model is as follows: First, a simulation model of the 500kA green anode cooling process was established using the method for establishing a green anode cooling model in electrolytic aluminum. In this model: The initial cooling temperature T0 of the raw anode carbon block is 150℃; the critical temperature point for flexural strength T is 80℃; the highest temperature of interest during air cooling is T. 空MAX The temperature is 82℃; the minimum cooling thickness is 50mm. Secondly, actual production parameters on site were measured. Further simulation calculations and optimizations of the green anode cooling process were conducted, and the influencing factors of the carbon block's temperature of interest were calculated. The following suggestions are provided for the optimization of the cooling process: (1) Based on the analysis of the factors affecting the temperature of the key points and the temperature of the circulating cooling water when stacking charcoal blocks, it is recommended to reduce the temperature of the circulating water to about 40℃; (2) The test carbon block stays in the cooling water pool for 84 minutes. It is recommended to extend the cooling water time to 90-100 minutes. Based on an average of 2.5 minutes / carbon block, there should be 36-40 carbon blocks in the pool. If it is summer and the ambient temperature exceeds 21℃, it is recommended to keep more than 40 carbon blocks in the pool. (3) After the raw blocks are removed from the water, they enter the plate chain air cooling and heat dissipation. The temperature of the point of concern will rise for 30-40 minutes. It is recommended to carry out regular stacking operations according to the continuous production mode of raw blocks, rather than using the plate chain to carry out two consecutive stacking operations when the raw blocks are full. (4) When spring turns into summer, the ambient temperature increases, so it is necessary to pay attention to the circulating water temperature and water cooling time. By lowering the circulating water temperature and extending the water cooling time, we can ensure that the temperature of the focus does not exceed the critical temperature during the natural cooling stage.

[0012] The beneficial effects of this invention are as follows: (1) This invention verifies the correlation between the compressive strength and flexural strength of the finished anode carbon block and temperature through experiments, and finds the critical temperature point for the flexural strength of the green anode carbon block; it also pays attention to the potential influence of the clamps on the force applied during the stacking of green anodes, and finds that the carbon block must be cooled to a certain temperature before its strength can resist the lifting force generated by the clamps, so as not to produce deformation or cracks; it finds that the carbon block does not need to be completely cooled, but the outer wall is cooled to the critical temperature point for flexural strength with a specific minimum cooling thickness, so as to resist the influence of the clamps on the finished product, and can shorten the time and route of the traditional cooling process; it determines the calculation method of the minimum cooling thickness, and performs quantitative and precise data management of the traditional empirical cooling process; it further develops a green anode cooling model and performs simulation calculations on it; and it verifies the cooling model multiple times in the analysis of the factors affecting the cooling of green anodes to ensure the matching between the model and actual production, and to ensure that the model can be adapted to various production lines of different scales and specifications in the application stage.

[0013] (2) The model of this invention is an open process model with strong practicality and large room for improvement. At present, it can guide the daily adjustment of cooling process parameters. There is still room for improvement in the future. Through a large amount of production data and further experiments, the technical factors of the current simplified model can be improved. Through continuous enrichment, a complete and easily dynamically adjustable green anode cooling process can be established, which can fundamentally solve the current extensive experience-based operation mode of green anode cooling, break the conventional understanding that cooling process is not linked to molding, and make the cooling process also participate in the production control system for improving anode quality. It also has positive significance for the transformation of some production lines with tight factory space, so that long-distance chain plate conveying can provide a large transformation space. Attached Figure Description

[0014] Figure 1 A schematic diagram illustrating the theoretical relationship between the compressive strength of the anode and temperature; Figure 2 This is a graph showing the compressive strength test results at 90°C in S1.2 of Example 1; Figure 3 This is a graph showing the compressive strength test results at 100°C in S1.2 of Example 1; Figure 4 This is a simulation cloud diagram of the force at the center of the raw block in S2.1 of Example 1; Figure 5 This is a simulation cloud diagram of the force on the end face of the raw block in S2.1 of Example 1; Figure 6 The temperature distribution curve along the center line of the carbon block is plotted after summarizing the experimental data in S2.2 of Example 1. Figure 7 This is a schematic diagram of the green anode dimensions in S2.2 of Example 1; Figure 8 This is a force analysis diagram of the carbon block under the clamp operation in S2.3 of Example 1; Figure 9 This is the geometric model of the green anode water cooling process in S3.1 of Example 1; Figure 10 This is the geometric model of the air-cooling process for the green anode in S3.1 of Example 1; Figure 11 The simulation results of temperature cloud map changes during the water cooling process of the green anode in S3.3.1 of Example 1 (unit: K); Figure 12 The simulation results of temperature cloud map changes during the air cooling process of the green anode in S3.3.2 of Example 1 (unit: K); Figure 13 The temperature curve calculated by combining water cooling and air cooling for the green anode in S3.3.3 of Example 1; Figure 14 The curve showing the effect of molding temperature on water cooling in S4.1 of Example 1; Figure 15 The curve showing the effect of water cooling time on water cooling effect in S4.2 of Example 1; Figure 16 The curve showing the effect of circulating cooling water temperature on water cooling effect in S4.3 of Example 1 is shown. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Therefore, the following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0017] Example 1 A method for establishing a cooling model for the green anode of electrolytic aluminum, comprising the following steps: S1. Experiment exploring the relationship between the strength of the anode and temperature; S1.1 Theoretical relationship between the strength of the green anode and temperature; According to the references, when the temperature of the green anode is close to or above the softening point of the asphalt, its mechanical stability is very low. Compressive strength can effectively reflect the sensitivity of the anode structure.

[0018] Figure 1 This indicates that the compressive strength of green anodes is stable at around 70℃, but decreases sharply when the material begins to exhibit significant elastoviscous behavior. The critical temperature varies with the softening point of the asphalt. Similarly, influenced by the softening point of the asphalt, the flexural strength of green anodes gradually decreases as the temperature gradually increases, and the critical temperature remains consistent. S1.2 Experimental data on the relationship between green anode strength and temperature; To verify the accuracy of the above theoretical relationship, accurate laboratory data is needed.

[0019] Our company samples the raw blocks produced and conducts strength tests on them. At the same time, backup samples are used to complete the strength-temperature relationship test in the laboratory.

[0020] Our company uses an imported mixing and molding machine for raw blocks. The raw block asphalt content is about 14.5%. The compressive strength and flexural strength of the sampled raw blocks (one for use and one for backup) were tested at different temperatures. The data are shown in Table 1.

[0021] Table 1 Summary of data on the relationship between green block strength and temperature As shown in Table 1, the compressive strength of the green biscuit decreases significantly after 70℃, and the flexural strength decreases significantly after 80℃. It can be considered that the critical temperature for the flexural strength of the green biscuit is 80℃.

[0022] S2. Calculation of minimum cooling thickness for green anode; S2.1, Simulation of the stress on the raw anode stack; In actual production, after the green anode is cooled in a water tank, it enters the conveyor chain for natural cooling. When the number of green blocks on the chain exceeds a certain amount (21 blocks in our production line in this embodiment), the stacking crane in the green block warehouse begins to clamp the carbon blocks. At this time, the green blocks will be subjected to external pre-tightening force generated by the clamps. The pre-tightening force at this moment is simulated and calculated.

[0023] Using the simulation module in SolidWorks, preload was applied to the two small end faces of the carbon block. The force on the center face of the green block mainly came from the clamping pressure on the end faces, which is a transmission of pressure. The greatest pressure was at the center of the face. This preload can be divided into frictional force and bending resistance factors. The simulation calculation results are as follows. Figure 4 The diagram shows a simulated force cloud at the center of the carbon block. However, this is not the focus of this embodiment. This embodiment focuses on the relationship between the force causing the carbon block to deflect due to the static friction force generated by the pressure on both sides and the flexural strength of the carbon block.

[0024] The simulation result of this relationship is as follows: Figure 5 The diagram shows the stress simulation contour plot of the raw block cross-section. (From...) Figure 5 It is known that when a green billet is subjected to the lifting force of a clamp, it generates an upward resistance, which is actually static friction. The end face is the location where the lifting force is greatest, generating compressive force on the top surface and tensile force on the bottom surface. The interaction between these two forces produces a certain degree of deflection. Therefore, the carbon block must be cooled to a certain temperature so that its strength is sufficient to resist the lifting force generated by the clamp and to prevent deformation or cracking.

[0025] S2.2, Minimum cooling thickness t; Based on laboratory data on the strength and temperature of green briquettes in S1, the critical temperature for flexural strength is determined to be around 80℃. This means that if the green briquette temperature exceeds 80℃ during cooling, its compressive and flexural strength will be insufficient to withstand the preload of the clamps when operated by the stacking crane, resulting in surface or internal cracks in the charcoal. Only when the green briquette temperature is below 80℃ does its strength reach a level high enough to resist the preload of the clamps.

[0026] However, after the carbon block is cooled by circulating water, the internal temperature distribution is uneven and there is a large temperature gradient, which can be seen from the simulation calculation results. Therefore, we need to calculate the minimum cooling thickness t that the carbon block can resist the clamping preload. As long as the temperature of the carbon block in this thickness area is below 80℃, the carbon block will not deform or crack due to the external clamping preload.

[0027] At this point, further experiments are needed. After the carbon block has been cooled in a water tank for 30 minutes, the temperature data along the horizontal centerline, from the center of the carbon block to its outer surface, is collected and plotted. Figure 6 The temperature distribution curve along the centerline of the carbon block is shown.

[0028] Depend on Figure 6 It can be seen that during the cooling process, the carbon block dissipates heat to the surroundings, and the temperature of the carbon block gradually decreases from the center to the surface. When the temperature of the carbon block from a certain area in the center to the surface area is all below the critical temperature of flexural strength, the thickness of that area, that is, the distance from that point to the surface, is called the minimum cooling thickness t.

[0029] For ease of understanding, use Figure 7 To illustrate. Figure 7 In this context, 'a' represents the height of the carbon block (excluding the boss), 'b' represents the width of the carbon block, 'c' represents the length of the carbon block, and 't' represents the minimum cooling thickness defined above.

[0030] S2.3 Calculation of minimum cooling thickness t; Based on the size of the char blocks, the force analysis of the clamps on the char blocks during the overhead crane stacking process is as follows: Figure 8 As shown, based on the force analysis: ∑Fx=0 can be used to deduce that Fleft=Fright=Fsupport; ∑Fy=0 can be used to infer ; In this embodiment, the weight of the carbon block is known to be G = 1.28t, and the coefficient of friction is μ = 0.45; Pressure F = G / μ = 1280 ÷ 0.45 = 27876 N; In the dimensions of the charcoal block, a = 0.663m and b = 0.705m. According to the rectangular plate coefficient table, when b / a = 1.063, the coefficient c9 = 0.807 (refer to the table).

[0031] The minimum cooling thickness t is calculated using the qualified product data φr = 9 MPa, given the flexural strength limit of the carbon block. ; Based on the relationship between the strength and temperature curves of the green anode, it can be concluded that when the temperature in the outer region with a depth of 50mm from the surface to the center of the green anode is below 80℃, carbon block cracking will not occur under the clamps of the stacking crane.

[0032] S3, Development of a green anode cooling model; S3.1 Geometric Model and Mesh Generation; Based on the development experience of simulation models for the green anode cooling process, the simulation results required for this calculation are basically the same under both three-dimensional and two-dimensional models, provided that the mesh accuracy does not affect the calculation results. In order to shorten the calculation time, the two-dimensional model is used for calculation.

[0033] The developed water-cooled and air-cooled geometric models are as follows: Figure 9 and 10 As shown: The water-cooled geometric model for the green anode was meshed with 106,824 meshes, while the air-cooled model was meshed with 83,763 meshes. Mesh control and mesh refinement operations were implemented in the carbon block region, while significantly reducing the number of meshes. This allows the mesh size in the carbon block region to be set to 1-2 mm, thereby enabling monitoring of the temperature distribution at any thickness of the carbon block.

[0034] During the model building process, appropriate simplifications and assumptions were made to the geometric model, mainly including: (1) The raw anode carbon bowl and the chamfered structure around it were ignored; (2) The flow of the medium in the circulating water tank is not considered, and the cooling medium is in a static state; (3) To reduce the amount of calculation, a symmetrical structure is set up, with the carbon block located in the center of the pool; (4) Ignoring the adjacent carbon blocks, the adjacent carbon blocks actually have an impact on heat transfer.

[0035] S3.2, Physical properties and boundary conditions; In this calculation model, the physical properties of the green body, including specific heat and thermal conductivity, have a significant impact on the calculation results. Based on literature review and actual measurement data from the University of Auckland, the physical properties of the green body are as follows: (1) Specific heat of the anode: The specific heat is a function of temperature: ; Where T is the thermodynamic temperature, K; a=42.52094, b=3.18657, c=-0.00172, d=3.1×10 -7 ; (2) Thermal conductivity of the green anode: The thermal conductivity is a function of temperature. ; Where T is the thermodynamic temperature, K; A=-9.103, B=0.0569, C=-8.602×10 -5 D = 5.756 × 10 -8 E = -1.38 × 10 -11 ; In the research and development phase prior to this embodiment, a small-scale electrolytic aluminum green anode carbon block cooling device was used to simulate the actual cooling process, and the technical concept of the present invention was verified multiple times and under multiple factors. After confirmation, the boundary conditions calculated in this embodiment adopted data measured during actual stable production. The on-site test diagrams can be found in the substantive examination references.

[0036] S3.3 Simulation Calculation Results; (1) Water-cooling simulation results; After establishing the two-dimensional geometric model, meshing, and setting boundary conditions, the simulation results of the carbon block temperature distribution are as follows: Figure 11 As shown.

[0037] The figure shows the temperature distribution of the carbon block along the width direction at t=0, t=30min, t=60min and t=84min. Since the heat transfer method used in the calculation is heat conduction, the overall result conforms to the temperature distribution law of heat conduction and heat transfer. The heat in the center of the carbon block is gradually transferred to the surrounding area through the cooling water, and the temperature shows a slow decreasing trend. The temperature in the central area is the highest, and the temperature around the carbon block shows an obvious temperature gradient.

[0038] (2) Simulation results of air cooling; As we currently understand that most domestic green anode cooling processes involve cooling in a water tank for a period of time, followed by natural cooling, and then transporting the green anode blocks to the green anode storage area via a plate chain. The blocks gradually accumulate on the plate chain, and operation begins when the quantity reaches the amount required for one operation of the stacking crane. Therefore, the air cooling time for each carbon block is different, ranging from as long as 90 minutes to as short as 30 minutes.

[0039] Therefore, this embodiment is simplified based on the actual air-cooled model.

[0040] The heat dissipation space is actually the top space of the entire conveyor chain, but considering modeling and mesh calculation issues, it is appropriately simplified, and only the top 3m space is considered. The simplified simulation results are as follows. Figure 12 As shown in the figure, the temperature change of the carbon block under natural heat dissipation conditions of air cooling after water cooling of the raw anode can be seen intuitively from the figure: after 120 minutes of air cooling, the average temperature decreases, but the decrease is limited, which depends on the heat dissipation conditions of the carbon block chamber and parameters such as ambient temperature.

[0041] (3) Simulation calculation results of the green anode cooling process; Combining the results of water cooling and air cooling, the simulation calculation results of the green anode cooling process are as follows: Figure 13 As shown, this represents the entire green anode cooling process, including water bath cooling in the pool and natural air cooling on the plate chain.

[0042] As shown in the graph, the water bath cooling lasted 84 minutes, and the remaining calculation was 120 minutes of air cooling. During this process, the average temperature of the charcoal block dropped rapidly during the water bath process, and while it also showed an overall temperature decrease during the air cooling process, the rate of decrease became significantly slower.

[0043] In summary, the analysis of the average temperature of the carbon block is not particularly meaningful, as it cannot reveal any relationship between strength and temperature, or any inherent quality issues. However, we can observe that the temperature point 50mm below the surface of the carbon block is the most important.

[0044] from Figure 13 As can be seen above, the temperature at this point drops rapidly during the water cooling process, mainly due to the temperature difference between the high-temperature carbon block and the low-temperature circulating cooling water, as well as the fact that it is not far from the surface of the carbon block. During the 84-minute water cooling process, the temperature at this point drops from 150°C to about 80°C.

[0045] However, after exiting the water bath, the heat transfer mechanism changes fundamentally. Influenced by the heat transfer method and the ambient temperature, the temperature at this point gradually increases and then decreases. This is mainly because in a water bath, the maximum heat transfer coefficient can reach 1000 W / m²·K, while in natural convection, the maximum heat transfer coefficient decreases significantly, to 1.5-5 W / m²·K. 2 Between K and K, the two are not on the same order of magnitude. Therefore, the heat transfer from the surface of the carbon block to this location suddenly slows down. However, the rate at which heat is transferred from the inside of the carbon block to this location is still comparable to the heat transfer rate in the previous water bath. This means that less heat is going out and more is coming in, so the temperature will gradually rise. Only after the heat transfer inside the carbon block and the surface heat transfer reach equilibrium again will the temperature at a depth of 50mm gradually decrease.

[0046] Assuming that the laboratory data on the strength and temperature of the charcoal block in this example yields a critical cooling temperature of 80°C, then... Figure 13 As shown, the time of intersection between the temperature at the minimum cooling thickness t and the critical cooling temperature during the air cooling temperature rise is t1, and the time of intersection during the air cooling temperature fall is t2. During the cooling time t1-t2, the temperature in the minimum cooling thickness region exceeds the critical cooling temperature. According to the stress analysis, if the carbon blocks are stacked during this period, the strength of this region is insufficient to support the impact of the clamps, which can easily lead to internal cracks in the carbon blocks. However, the highest temperature at the point of concern during air cooling is 82℃, which exceeds the critical temperature by 2℃. Therefore, it is necessary to strictly control the water cooling time so that the highest temperature of the carbon blocks at the point of concern during the reheating stage after water removal is lower than the critical cooling temperature.

[0047] S4. Analysis of factors affecting the cooling of the green anode; S4.1 The effect of molding temperature; In existing technologies, different molding processes for raw anode carbon blocks result in different mixing temperatures and mixing effects of the paste, naturally leading to different molding temperatures. For continuous processes, the molding temperature is 155-160℃, while for intermittent processes, the molding temperature is controlled at 150-155℃.

[0048] Using a validated simulation model, the temperature at a depth of 50mm in the carbon block was calculated corresponding to a molding temperature range of 140℃ to 165℃. Figure 14 As shown, the effect of molding temperature on the temperature of interest is basically a positive linear relationship; for every 5°C increase in molding temperature, the temperature of interest increases by 1.2°C.

[0049] S4.2, Water cooling time; During the construction phase of a project, each manufacturer faces limitations in the overall layout, resulting in varying cooling area areas in the green anode water tanks. This leads to significant differences in the time the green anode remains in the tank after forming, ranging from less than 30 minutes to as long as 150 minutes. The effect of cooling time on the temperature of the point of interest is illustrated in the curve below. Figure 15 As shown in the figure, there is a non-linear negative correlation between water cooling time and the temperature of interest. The temperature drops rapidly in the first 40 minutes after the carbon block enters the water tank, and the rate of temperature drop slows down after 60 minutes. In the first hour, the temperature of interest drops by 60°C, and in the next two hours, it drops by 18°C. Therefore, the water tank cooling process in the green anode water cooling process is not better the longer it is. It needs to be adjusted according to the actual production situation. The water tank cooling time should be shortened as much as possible without affecting the quality of the carbon block.

[0050] S4.3, Circulating cooling water temperature; In the water-cooling process for green anodes, the circulating cooling water temperature is a crucial parameter, especially since this parameter varies with the seasons. Its impact on the cooling effect is illustrated in the curve below. Figure 16 As shown, the circulating cooling water temperature and the point of interest temperature have a linear positive correlation. The higher the cooling water temperature, the smaller the temperature between the cooling water and the carbon block, the worse the cooling effect, and the higher the point of interest temperature. For every 5°C increase in cooling water temperature, the point of interest temperature increases by 3°C.

[0051] This embodiment focuses on the modeling method; for specific applications, see Embodiment 2.

[0052] Example 2 The application of the electrolytic aluminum green anode cooling model establishment method described in Example 1 includes: S5, model application; First, a simulation model of our company's 500kA green anode cooling process was established using the method in Example 1; Secondly, actual production parameters on site were measured. Further simulation calculations and optimizations of the green anode cooling process were conducted, and the influencing factors of the carbon block's temperature of interest were calculated. The following suggestions are provided for the optimization of the cooling process: (1) The average temperature of the circulating cooling water on the day of the test was 44℃. Based on the analysis of the factors affecting the temperature of the focus point and the temperature of the circulating cooling water when stacking the carbon blocks, it is recommended to reduce the temperature of the circulating water to about 40℃. (2) The test carbon block stays in the cooling water pool for 84 minutes. It is recommended to extend the cooling water time to 90-100 minutes. Based on an average of 2.5 minutes / carbon block, there should be 36-40 carbon blocks in the pool. If it is summer and the ambient temperature exceeds 21℃, it is recommended to keep more than 40 carbon blocks in the pool. (3) After the raw blocks are removed from the water, they enter the plate chain air cooling and natural heat dissipation. The temperature of the focus point will rise to a certain extent and last for about 30-40 minutes. It is recommended to carry out regular stacking operations according to the continuous production mode of raw blocks, rather than using the plate chain to carry out two consecutive stacking operations when the raw blocks are full. (4) When spring turns into summer, the ambient temperature increases. Pay more attention to the circulating water temperature and water cooling time. It is recommended to appropriately reduce the circulating water temperature and extend the water cooling time to ensure that the temperature of the focus does not exceed the critical temperature during the natural cooling stage.

[0053] Finally, production process parameters were adjusted in accordance with the cooling process optimization recommendations before production commenced.

[0054] Comparing the quality of anode carbon blocks produced before and after process optimization, and randomly sampling anode carbon blocks produced before and after process optimization, their compressive strength was tested. Generally, the strength of anode carbon blocks produced after process optimization was better than that of anode carbon blocks produced before process optimization.

[0055] It is evident that the model establishment method of S1-4 in this invention is effective, and the results are easy to apply.

[0056] It should be noted that this embodiment is only a very common application and test in the cooling process of green anode carbon blocks. Other production lines have different green anode water pool cooling areas, water cooling and air cooling conditions, different plate chain lengths, and different top spaces of the conveyor plate chain. They can all be adjusted and modeled according to the actual workshop conditions before application.

Claims

1. A method for establishing a cooling model for the green anode of electrolytic aluminum, characterized in that, This method consists of the following steps: S1. Experiment exploring the relationship between the strength of the anode and temperature; Samples of the produced raw blocks were taken and their strength was tested. Meanwhile, backup samples were used to test the relationship between strength and temperature in the laboratory. The test results will show a specific temperature T℃. After this specific temperature, the flexural strength will decrease significantly. The critical temperature point for the flexural strength of the green body is determined to be T℃. S2. Calculation of minimum cooling thickness for green anode; S2.1, Simulation of the stress on the raw anode stack; After being cooled in a water tank, the green anodes are naturally cooled by a conveyor chain. When the number of green blocks on the chain exceeds the number set when the production line was built, the stacking crane in the green block warehouse begins to clamp the carbon blocks. At this time, the green blocks will be subjected to external force generated by the clamps. The external force at this moment is simulated and calculated, and the conclusion is that the carbon blocks must be cooled to a certain temperature so that their strength is sufficient to resist the lifting force generated by the clamps and will not deform or crack. S2.2, Minimum cooling thickness t; According to S1, the critical temperature for flexural strength is 80℃. This means that if the temperature of the green block is higher than 80℃ during the cooling process, the compressive and flexural strength of the green block cannot resist the pre-tightening force of the clamp when the stacking crane clamp operates on it, and surface or internal cracks will appear in the carbon block. Only when the temperature of the green block is lower than 80℃ can the green block strength be high enough to resist the pre-tightening force of the clamp. However, after the carbon block is cooled by circulating water, the internal temperature distribution is uneven and there is a large temperature gradient. Therefore, it is necessary to calculate the minimum cooling thickness t that the carbon block can withstand the clamping force. That is, as long as the temperature of the carbon block in this thickness area is below 80℃, the carbon block will not deform or crack due to the external clamping force. At this point, further experiments are needed to collect temperature data from the center of the carbon block to its outer surface along the horizontal centerline after the carbon block has been water-cooled for 30 minutes, in order to plot the temperature distribution curve along the centerline of the carbon block. The curve drawn can express the trend of the carbon block dissipating heat to the surroundings during the cooling process. The temperature of the carbon block gradually decreases from the center to the surface. When the temperature of the carbon block from a certain area in the center to the surface area is all below the critical temperature of flexural strength, the thickness of that area, that is, the distance from that point to the surface, is called the minimum cooling thickness t. S2.3 Calculation of minimum cooling thickness t; The force analysis of the clamps on the charcoal blocks during the stacking process by the overhead crane is as follows: From ∑Fx=0, we can deduce that the force on the carbon block is Fleft = Fright; ∑Fy=0 can be used to infer ; The minimum cooling thickness t can be calculated based on the flexural strength data of the carbon block: ； c9 is a coefficient; Based on the relationship between the strength and temperature curves of the green anode, it can be concluded that when the temperature in the outer region from the surface of the green anode to the center at a depth of t is lower than T℃, the carbon block cracking problem will not occur under the clamps of the stacking crane. S3, Development of a green anode cooling model; S3.1 Geometric Model and Mesh Generation; The calculation is performed using a two-dimensional model; The first developed geometric models were water-cooled and air-cooled; Next, mesh the two according to the geometric model; mesh control and mesh refinement operation of the carbon block area, set the mesh of the carbon block area to 1-2mm to facilitate monitoring the temperature distribution of the carbon block at any thickness; S3.2, Physical properties and boundary conditions; The physical properties of the green body, including specific heat and thermal conductivity, have a significant impact on the calculation results. These properties can be obtained by consulting literature and actual measurement data. (1) Specific heat of the anode: The specific heat is a function of temperature: ; Where T is the thermodynamic temperature, K; a=42.52094,b=3.18657,c=-0.00172,d=3.1×10 -7 ; (2) Thermal conductivity of the green anode: The thermal conductivity is a function of temperature. ; Where T is the thermodynamic temperature, K; A=-9.103,B=0.0569,C=-8.602×10 -5 ,D=5.756×10 -8 ,E=-1.38×10 -11 ; S3.3 Simulation Calculation Results; (1) Water-cooling simulation results; After establishing the two-dimensional geometric model, meshing, and setting boundary conditions, the temperature distribution of the carbon block in the simulation can be plotted, focusing on different time points t. 水1 ...t 水n Does the temperature distribution along the width of the carbon block conform to the temperature distribution law of heat conduction and heat transfer? That is, the heat in the center of the carbon block is gradually transferred to the surrounding area through the cooling water, and the temperature shows a slow downward trend. The temperature in the center area is the highest, and the temperature around the carbon block shows a clear temperature gradient. If the temperature distribution diagram of the carbon block calculated by simulation conforms to the above-mentioned temperature distribution law of heat conduction and heat transfer, then the simulation calculation is usable; if it does not conform, it is necessary to check whether the physical property parameters of the green body are appropriate and make corrections until the temperature distribution diagram of the carbon block calculated by simulation conforms to the above-mentioned temperature distribution law of heat conduction and heat transfer. (2) Simulation results of air cooling; Because the air-cooling conditions vary greatly among production enterprises, this step is simplified based on the actual air-cooling model. The heat dissipation space is simplified to only consider the top 3m space of the conveyor chain; After simplification, the simulation results show the temperature change of the carbon block under the condition of water cooling followed by air cooling and natural heat dissipation: air cooling t 空n Minutes later, the average temperature began to drop, but the drop was limited. (3) Simulation calculation results of the green anode cooling process; Combining the results of water cooling and air cooling, the simulation calculation results of the green anode cooling process can be obtained, which represents the entire green anode cooling process, including water bath cooling in the water tank and natural air cooling process on the plate chain. The temperature at the minimum cooling thickness is defined as the point of concern. Its behavior throughout the cooling process is as follows: This point of concern temperature drops rapidly during water cooling, but after water exit, it gradually increases and then decreases during the air cooling stage. It is necessary to control the highest temperature T of the carbon block during the reheating stage of the point of concern after water exit. 空MAX ℃ is below the critical cooling temperature T℃; S4. Analysis of factors affecting the cooling of the green anode; S4.1 The effect of molding temperature; Focusing on the actual molding temperature of the raw anode carbon block during production and extending this range, the temperature at the minimum cooling thickness t of the carbon block corresponding to the molding temperature range of 140℃ to 165℃ is calculated to verify the simulation model. The model is then examined to see if the influence of the molding temperature on the temperature of interest is basically positively linear. If it is linear, the model passes the verification; otherwise, it is necessary to trace back and re-analyze the factors in the model. S4.2, Water cooling time; There is a non-linear negative correlation between the water cooling time and the temperature of interest after green body forming. By testing different water cooling times and temperatures of interest, the influence curve of cooling time on the temperature of interest can be plotted. Based on this curve, the cooling time in the water tank can be dynamically adjusted to ensure that the water cooling time is shortened as much as possible without affecting the quality of the charcoal blocks. S4.3, Circulating cooling water temperature; In the green anode water cooling process, the circulating cooling water temperature is a very important parameter. This parameter changes with the seasons. The effect curve of cooling time on the temperature of the point of interest can be plotted by testing the circulating cooling water temperature and the temperature of the point of interest. The circulating cooling water temperature can be dynamically adjusted using this curve.

2. The method for establishing a cooling model for the green anode of electrolytic aluminum as described in claim 1, characterized in that: The simulation calculation in S2.1 uses the simulation module in SolidWorks, focusing on the relationship between the force causing the carbon block to deflect due to the static friction force on the surface generated by the pressure on both sides of the fixture and the flexural strength of the carbon block; the simulation calculation result of this relationship can be expressed as a simulated cloud diagram of the stress on the cross section of the raw block; When the green billet is subjected to the lifting force of the clamp, it will generate an upward resistance, which is actually a static friction force; The end face is the position subjected to the greatest lifting force. Extrusion force is generated on the top surface of the green billet, and tension force is generated on the bottom surface. The interaction between the two will produce deflection. Therefore, the carbon block must be cooled to a certain temperature so that its strength is sufficient to resist the lifting force generated by the fixture and will not deform or crack.

3. The method for establishing a cooling model for the green anode of electrolytic aluminum as described in claim 2, characterized in that: In the process of establishing the model in S3.1, appropriate simplifications and assumptions were made to the geometric model, mainly including: (1) The raw anode carbon bowl and the chamfered structure around it were ignored; (2) The flow of the medium in the circulating water tank is not considered, and the cooling medium is in a static state; (3) To reduce the amount of calculation, a symmetrical structure is set up, with the carbon block located in the center of the pool; (4) Ignoring the adjacent carbon blocks, the adjacent carbon blocks actually have an impact on heat transfer.

4. The method for establishing a cooling model for the green anode of electrolytic aluminum as described in claim 3, characterized in that: The derivation process of the temperature of the carbon block at the point of concern after effluent in S3.3 is as follows: Firstly, the temperature at this point drops rapidly during water cooling, primarily due to the temperature difference between the high-temperature carbon block and the low-temperature circulating cooling water, as well as the proximity to the carbon block surface. The temperature at this location drops from t... 水1 ...t 水n During the water cooling process over a period of time, the initial cooling temperature T0℃ of the green anode carbon block (the temperature at which it enters the water cooling process after molding) drops to around T℃, the critical temperature point for flexural strength. Secondly: After water discharge, the temperature at the point of interest during the air-cooling stage shows a trend of gradually increasing and then decreasing: the highest temperature of the reheating stage in this air-cooling stage is set as T. 空MAX ℃; The laboratory data on the strength and temperature of the anode carbon block obtained in S1 show that the critical temperature point for flexural strength is T℃, which is also called the critical cooling temperature, T℃. The time t is the intersection point between the temperature at the minimum cooling thickness t and the critical cooling temperature during the air cooling temperature rise process. 空1 The time t is the intersection point between the air-cooled temperature decrease and the critical cooling temperature. 空2 During the cooling time t 空1 -t 空2 During the process, the temperature of the minimum cooling thickness area exceeds the critical cooling temperature. According to the stress analysis, if the carbon blocks are stacked during this period, the strength of this area is insufficient to support the impact of the clamp, which may easily lead to internal cracks in the carbon blocks. However, the temperature of highest concern during air cooling is T. 空MAX ℃, exceeding the critical cooling temperature (T 空MAX -T)℃, therefore the water cooling time t needs to be strictly controlled. 水n This causes the highest temperature T of the charcoal block during the reheating stage after water discharge to be of concern. 空MAX ℃ is below the critical cooling temperature T℃.

5. An application of a method for establishing a cooling model for the green anode of electrolytic aluminum, characterized in that, The method described in claim 4 is applied to a 500kA green anode cooling process; The specific application of the model is as follows: First, a simulation model of the 500kA green anode cooling process was established using the method for establishing a green anode cooling model in electrolytic aluminum. In this model: The initial cooling temperature T0 of the raw anode carbon block is 150℃; the critical temperature point for flexural strength T is 80℃; the highest temperature of interest during air cooling is T. 空MAX The temperature is 82℃; the minimum cooling thickness is 50mm. Secondly, actual production parameters on site were measured. Further simulation calculations and optimizations of the green anode cooling process were conducted, and the influencing factors of the carbon block's temperature of interest were calculated. The following suggestions are provided for the optimization of the cooling process: (1) Based on the analysis of the factors affecting the temperature of the key points and the temperature of the circulating cooling water when stacking charcoal blocks, it is recommended to reduce the temperature of the circulating water to about 40℃; (2) The test carbon block stays in the cooling water pool for 84 minutes. It is recommended to extend the cooling water time to 90-100 minutes. Based on an average of 2.5 minutes / carbon block, there should be 36-40 carbon blocks in the pool. If it is summer and the ambient temperature exceeds 21℃, it is recommended to keep more than 40 carbon blocks in the pool. (3) After the raw blocks are removed from the water, they enter the plate chain air cooling and heat dissipation. The temperature of the point of concern will rise for 30-40 minutes. It is recommended to carry out regular stacking operations according to the continuous production mode of raw blocks, rather than using the plate chain to carry out two consecutive stacking operations when the raw blocks are full. (4) When spring turns into summer, the ambient temperature increases, so it is necessary to pay attention to the circulating water temperature and water cooling time. By lowering the circulating water temperature and extending the water cooling time, we can ensure that the temperature of the focus does not exceed the critical temperature during the natural cooling stage.

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