Graphitization process of graphite electrode with extra-large diameter

Abstract

The invention discloses a graphitization process of an extra-large-diameter graphite electrode, and relates to the technical field of carbon material manufacturing, and the graphitization process comprises the following steps: preparing for charging, distributing resistance, precisely machining the end surface of a roasted product electrode, and matching according to the resistivity. The method comprises the following steps: precisely machining the end surface of the roasted product electrode; strictly matching the electrodes of the same furnace according to the resistivity to ensure that the range is less than 5 mu omega.m, and matching the furnace resistance of the two furnaces in parallel power transmission; by adopting a large-head-to-small-head series connection column assembling mode, the resistivity is as low as about 10 mu omega.m, and the performance is excellent and stable; the direct heating of the internal skewering furnace is combined with the optimized power transmission curve, so that the production efficiency is greatly improved; according to the whole process, parameterized and monitorable closed-loop control of the whole process is achieved from furnace charging resistance distribution and constant-current power transmission to spray cooling, and the method is particularly suitable for large-scale and stable production of electrodes with extra-large diameters.

Description

Technical Field

[0001] This invention relates to the field of carbon material manufacturing technology, specifically to a graphitization process for ultra-large diameter graphite electrodes. Background Technology

[0002] Graphitization is the core process in the production of artificial graphite electrodes. It involves heat-treating the calcined material at temperatures above 2000℃ to transform the disordered arrangement of carbon atoms into an ordered graphite crystal structure, thereby achieving excellent electrical, thermal, and mechanical properties. With the increasing demand for large-scale submerged arc furnaces in industries such as metallurgy and chemicals, the need for ultra-large diameter, ultra-high power graphite electrodes with diameters of 1200mm-1400mm is becoming increasingly urgent.

[0003] However, graphitization of such extra-large diameter electrodes presents the following challenges: 1. Extremely high risk of thermal stress cracking: The electrode cross-section is huge. During the heating process (especially the endothermic stage of the drastic transformation of carbon structure at 1000℃-1800℃) and cooling process, the huge internal and external temperature difference will generate uncontrollable thermal stress, which can easily lead to cracks inside or at the end of the product, making it difficult to guarantee the yield. 2. High energy consumption and long cycle: Traditional Atchison furnaces use indirect heating, which has low thermal efficiency and a power supply cycle of 50-70 hours. The power consumption per ton exceeds 4000kWh, resulting in high production costs. 3. Poor performance uniformity: Large cross-section products are heated unevenly in traditional furnaces, which can easily lead to uneven resistivity distribution and affect their performance. 4. Inefficient process control: Existing processes rely heavily on constant power or empirical curves, which cannot accurately match the physicochemical changes of materials in different temperature zones, resulting in poor process stability.

[0004] While the internal series graphitization furnace improves thermal efficiency, the contradiction between thermal stress control and refined process management becomes more prominent when it is directly applied to extra-large diameter electrodes.

[0005] Therefore, this invention requires the design of a graphitization process for ultra-large diameter graphite electrodes to solve the aforementioned problems. Summary of the Invention

[0006] The purpose of this invention is to provide a graphitization process specifically designed for ultra-large diameter graphite electrodes to solve the aforementioned problems. This process aims to significantly reduce product resistivity, stably increase the yield to over 98%, while substantially shortening the production cycle, reducing energy consumption, and ensuring high uniformity of product performance. The graphitization process for ultra-large diameter graphite electrodes solves the problems mentioned in the background art.

[0007] To address the above problems, the present invention provides a technical solution: A graphitization process for an ultra-large diameter graphite electrode includes the following specific steps: S1. Furnace preparation and resistance matching: The electrode end faces of the roasted products are precisely machined and matched according to resistivity to ensure that the resistivity difference of electrodes in the same furnace is less than 5μΩ·m. S2. Non-equal diameter end pressure series loading: Multiple non-equal diameter roasted electrodes are connected in series through a flexible graphite pad to form an electrode column, and a constant axial pressure of not less than 60 tons is applied to the entire electrode column and maintained throughout the process. S3. Robust constant current power supply: Power supply is carried out using a constant current control mode. The power supply process includes a rapid preheating period, a pyrolysis and reshaping period, and a graphitization improvement period, which are carried out in sequence. During the pyrolysis and reshaping period, the heating rate is controlled within the range of 30-50℃ / h. Furthermore, the axial displacement of the electrode post is monitored in real time during the power supply process, and the current control parameters are dynamically fine-tuned based on the displacement change trend to keep the displacement change stable. S4. Coordinated and controllable cooling: After power supply is completed, the axial pressure is maintained and the exhaust gas is collected. Then, controllable cooling is carried out. By spraying mist water onto the furnace body, the furnace core cooling rate is controlled at ≤20℃ / h until the furnace core temperature drops below 420℃ before being unloaded.

[0008] In a preferred embodiment of the present invention, in step S1, furnace resistance matching is performed on the electrode posts of the two furnaces that are connected in parallel to ensure that the total furnace resistance of the two furnaces is equal.

[0009] In a preferred embodiment of the present invention, the series connection method in step S2 is large end to small end; the specifications of the flexible graphite pad are matched with the dimensions of the non-equal diameter ends of the electrodes.

[0010] In a preferred embodiment of the present invention, the rapid preheating period in step S3 corresponds to room temperature to 900°C, during which the current rises rapidly; the pyrolysis reshaping period corresponds to 900°C to 1800°C, during which the current rises slowly; and the graphitization perfection period corresponds to above 1800°C, during which the current is first constant and then slowly decreases.

[0011] In a preferred embodiment of the present invention, the dynamic fine-tuning of the current control parameters based on the displacement change trend in step S3 refers to automatically reducing the rate of current increase when an abnormally rapid contraction trend is detected in the electrode column during the pyrolysis remodeling period.

[0012] In a preferred embodiment of the present invention, the controllable cooling in step S4 is intermittent quantitative spraying, specifically, every 4 hours, a fixed amount of mist water is sprayed into specific areas on both sides along the length of the electrode column.

[0013] In a preferred embodiment of the present invention, the amount of water sprayed each time is approximately 27 kg, and the flexible graphite pad is kept dry before use.

[0014] In a preferred embodiment of the present invention, the space between the electrode post and the furnace wall is filled with resistive material and heat-insulating material, and exhaust holes are provided at intervals along the length direction above the electrode post.

[0015] In a preferred embodiment of the present invention, the graphitization process requires connection to an electrical equipment system, which includes: The DC power supply subsystem has a rated DC output current ≥250kA and a constant current automatic control function with a current control accuracy ≤±1%. The hydraulic pressurization subsystem is configured to apply a constant axial pressure of not less than 60 tons to the series-connected electrode columns, and has a constant pressure control function that ensures pressure fluctuations of ≤±5% throughout the power transmission process. The cooling subsystem employs a closed-loop pure water cooling system to cool the key components of the DC power supply subsystem and the hydraulic pressurization subsystem.

[0016] In a preferred embodiment of the present invention, the power equipment system further includes an intelligent control terminal, the intelligent control terminal comprising: The central control module has a pre-stored three-stage curve program for robust constant current power transmission. The displacement feedback module includes a sensor for real-time monitoring of the axial displacement of the electrode post and is communicatively connected to the central control module to feed back displacement change data to the central control module. The central control module is configured to: receive data from the displacement feedback module and, based on a preset displacement stability model, dynamically adjust the current control parameters output to the DC power supply subsystem during the power transmission process. The spray control module, connected to the central control module, is configured to control the spray device to perform the intermittent quantitative spraying according to instructions during the cooling phase.

[0017] The beneficial effects of this invention are as follows: The invention precisely processes the electrode end faces of the roasted product; strictly groups electrodes in the same furnace according to resistivity to ensure a range difference of less than 5 μΩ·m, and matches the furnace resistance of two furnaces connected in parallel; by using a large-end-to-small-end method, multiple electrodes are connected in series to form a column using a specially designed flexible graphite pad, and a constant axial pressure of no less than 60 tons is immediately applied and maintained throughout the subsequent process; a high-precision constant current DC power supply is used, executing a three-stage power delivery curve, with constant current as the core control mode throughout the process; non-equal diameter series connection and constant voltage ensure uniform current distribution and contact reliability, resulting in robust constant current. Flow and displacement feedback precisely control the most fatal thermal stress cracks in extra-large diameter electrodes from the source, increasing the yield from the industry standard of -95% to ≥98%, with a resistivity as low as approximately 10μΩ·m, exhibiting excellent and stable performance. The combination of direct heating in the internal furnace and optimized power supply curve shortens the power supply cycle to 30-36 hours and reduces the power consumption per ton to 3000-3500kWh, saving more than 20% energy compared to traditional processes and significantly improving production efficiency. The entire process, from furnace loading and resistance matching, constant current power supply to spray cooling, achieves parameterized and monitorable closed-loop control, making it particularly suitable for the large-scale and stable production of extra-large diameter electrodes. Attached Figure Description

[0018] For ease of explanation, the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0019] Figure 1 This is a flowchart illustrating the overall steps of the graphitization process for an extra-large diameter graphite electrode according to the present invention. Figure 2 This is a process flow diagram of the graphitization process for an extra-large diameter graphite electrode according to the present invention. Figure 3 This is a schematic diagram of the statistical data of product specifications in the graphitization workshop 2 in Example 2 of the graphitization process of an extra-large diameter graphite electrode of the present invention. Detailed Implementation

[0020] like Figure 1 , Figure 2 and Figure 3 As shown, the specific implementation adopts the following technical solution: A graphitization process for an ultra-large diameter graphite electrode includes the following specific steps: S1. Furnace preparation and resistance matching: The electrode end faces of the roasted products are precisely machined and matched according to resistivity to ensure that the resistivity difference of electrodes in the same furnace is less than 5μΩ·m. To perform furnace resistance matching on the electrode posts of two furnaces that are powered in parallel, it is necessary to ensure that the total furnace resistance of the two furnaces is equal. S2. Non-equal diameter end pressure series loading: Multiple non-equal diameter roasted electrodes are connected in series through a flexible graphite pad to form an electrode column, and a constant axial pressure of not less than 60 tons is applied to the entire electrode column and maintained throughout the process. The series connection is from large end to small end; the specifications of the flexible graphite pad are matched with the dimensions of the non-equal diameter ends of the electrodes; S3. Robust constant current power supply: Power supply is carried out using a constant current control mode. The power supply process includes a rapid preheating period, a pyrolysis and reshaping period, and a graphitization improvement period, which are carried out in sequence. During the pyrolysis and reshaping period, the heating rate is controlled within the range of 30-50℃ / h. Furthermore, the axial displacement of the electrode post is monitored in real time during the power supply process, and the current control parameters are dynamically fine-tuned based on the displacement change trend to keep the displacement change stable. The rapid preheating period corresponds to the temperature from room temperature to 900°C, during which the current rises rapidly; the pyrolysis and reshaping period corresponds to the temperature from 900°C to 1800°C, during which the current rises gradually; and the graphitization perfection period corresponds to the temperature above 1800°C, during which the current first remains constant and then decreases slowly. Dynamically fine-tuning the current control parameters based on displacement change trends refers to automatically reducing the rate of current increase when an abnormally rapid contraction trend is detected in the electrode column during the pyrolysis remodeling period. S4. Cooperative and controllable cooling: After power supply is completed, the axial pressure is maintained and the exhaust gas is collected. Then, controllable cooling is carried out. By spraying mist water onto the furnace body, the furnace core cooling rate is controlled at ≤20℃ / h until the furnace core temperature drops below 420℃ and then the furnace is unloaded. Controllable cooling is achieved through intermittent, metered spraying. Specifically, every 4 hours, a metered amount of mist water is sprayed into specific areas on both sides of the electrode column along its length.

[0021] The measured amount is approximately 27 kg of water sprayed each time, and the flexible graphite pad should be kept dry before use; The space between the electrode post and the furnace wall is filled with resistive material and heat-insulating material, and exhaust holes are provided at intervals along the length of the electrode post.

[0022] The graphitization process requires connection to an electrical equipment system, which includes: The DC power supply subsystem has a rated DC output current ≥250kA and a constant current automatic control function with a current control accuracy ≤±1%. The hydraulic pressurization subsystem is configured to apply a constant axial pressure of not less than 60 tons to the series-connected electrode columns, and has a constant pressure control function that ensures pressure fluctuations of ≤±5% throughout the power transmission process. The cooling subsystem employs a closed-loop pure water cooling system to cool the key components of the DC power supply subsystem and the hydraulic pressurization subsystem.

[0023] The power equipment system also includes an intelligent control terminal, which comprises: a central control module pre-stored with a three-stage curve program for robust constant current power transmission; a displacement feedback module containing a sensor for real-time monitoring of the axial displacement of the electrode column and communicating with the central control module to feed back displacement change data to the central control module; the central control module is configured to: receive data from the displacement feedback module and, according to a preset displacement stability model, dynamically adjust the current control parameters output to the DC power supply subsystem during power transmission; and a spray control module connected to the central control module, configured to control the spray device to perform intermittent quantitative spraying according to instructions during the cooling phase.

[0024] Example 1: Adjustment required by the present invention I. Requirements for the Equipment 1. DC power supply subsystem: Rated DC output current: ≥250kA; Output voltage range: 0-150VDC; Rectification and control method: A twelve-pulse thyristor rectification system is adopted, which must have a high-precision constant current automatic control function with a current control accuracy of ≤±1%; Cooling subsystem: The transformer, rectifier cabinet, water-cooled copper busbar and hydraulic clamps all adopt a closed-loop pure water cooling system with water resistivity ≥0.5MΩ·cm; 2. Hydraulic pressurization subsystem: Rated pressure: ≥60 tons (approximately 588KN, applied to the entire 1300mm diameter, 14 electrode posts). Control requirements: It has a constant pressure control function, and the pressure fluctuation is ≤±5% throughout the power transmission process.

[0025] II. Conditions for Roasted Products to be Placed in the Furnace 1. Precision machining of end faces: The two end faces of the electrode (including the truncated cone end face and the cylindrical end face) are milled flat with high precision to ensure that the flatness error of the contact surface with the flexible graphite pad is ≤0.8mm and the surface roughness Ra≤6.3μm; 2. Before loading into the furnace, based on the resistivity of the roasted product, perform furnace resistance balancing on the products entering the furnace, i.e., the resistivity difference between the electrodes of the roasted product should be <5μΩ·m. Statistically calculate the average resistivity and standard deviation of the electrodes of the roasted products entering the furnace, ensuring they conform to a normal distribution, i.e., X±S≥65.5%, X±2S≥95.5%, X±3S≥99.7%. Calculate the length of the electrode columns, based on the conductor resistivity formula R= The furnace resistance of the furnace is determined. Because the method of "one transformer supplying power to two furnaces of calcined electrode" is adopted simultaneously (to ensure that the utilization rate of the transformer meets the power grid requirements for the power factor of the equipment), it is necessary to ensure that the furnace resistances of the two furnaces with the calcined electrode installed are equal to ensure that there is no current deviation. At the same time, it is necessary to avoid abnormal shrinkage of a certain electrode on the electrode column due to temperature rise during graphitization, which would cause abnormal parameters due to untimely system pressure replenishment and affect the process judgment during power supply. III. Conditions for Charging Auxiliary Materials Thermal insulation material: Metallurgical coke or graphitized petroleum coke particles with a particle size of 0-2mm are used. Its function is to keep the temperature warm and prevent oxidation. It does not participate in electrical conduction and has a thickness of ≥750mm. Resistance material: Lay it around the electrode posts, covering it with 5-8mm of calcined petroleum coke or metallurgical coke, thickness... ≥ 150mm, taking advantage of its high contact resistance, to ensure that the current does not deviate; 3. Flexible graphitized pad: This is an important auxiliary material in this solution. The solution uses a non-uniform diameter end-to-end "large end to small end" column assembly method, with the following specifications: diameter Φ 外 1300 / Φ 内 One 800mm x 20mm thick pad is used at the connection between the electrode assembly pads at one end and the furnace head. The electrode column body is connected at the root with a Φ... 外 1000 / Φ 内 700mm x 20mm thickness; Quantity: 14 pieces; IV. Furnace Loading Conditions 1. Electrode post assembly: 1.1 Electrode posts are constructed using a "large end to small end" series connection. Normal electrodes are cylindrical, with equal diameters at ends A and B. Taking a 1300mm electrode as an example, the non-equal diameter ends (the diameter ratio of the large end (A) to the small end (B) is 1.3:1) are matched with a flexible graphite pad with a diameter Φ. 外 1300 / Φ 内 800×20mm thickness; Φ 外 1000 / Φ 内 700mm x 20mm thickness; the ratio of the conductive areas at both ends is 1:0.485; 1.2 The electrodes are connected using flexible graphite pads. Before use, the graphite pads must not be damp. 1.3. Apply a constant axial pressure of ≥60 tons (588KN) to the electrode column through a hydraulic pressurization system and maintain it throughout the entire process; 2. Furnace core composition: 2.1. Maintain a uniform spacing of ≥650mm between the electrode column and the horizontal furnace wall, and ensure that the electrode column is filled with 5-8mm thick resistance material with a thickness of 200mm on each side and 0-2mm thick insulation material with a thickness of ≥650mm on each side. Ensure that each particle size component is fully and uniformly filled, and that there is no particle size segregation. 2.2. Maintain a distance of ≥1000mm between the electrode post and the furnace bottom. From the furnace bottom upwards, install a 0-2mm insulation layer with a thickness of ≥850mm; and a 5-8mm resistance layer with a thickness of ≥150mm. 2.3. Maintain a distance of ≥950mm between the electrode post and the furnace top. From the electrode post upwards, install a 5-8mm resistance material layer with a thickness of ≥200mm; and a 0-2mm insulation material layer with a thickness of ≥750mm. 2.4 Along the length of the electrode column, directly above the electrode column resistive material layer, starting from the positive end of the furnace head, exhaust holes with a diameter of 400mm and a height of 750mm are set every 4.5m, and the inside is filled with calcined petroleum coke particles with a particle size of 8-25mm. 2.5 Flexible graphite pads are used in the gaps between the electrodes of the electrode post to reduce contact resistance and prevent electrolytic corrosion; V. Power Transmission Curve This power transmission curve is tailored to the characteristics of three material stages, and uses constant current as the core control mode throughout, employing robust constant current power transmission technology: The following analytical method, using expansion-displacement curves, is used to prevent product cracking: During the power supply process, when the product's temperature rises within the repeated roasting stage, the length of the electrode column exhibits a continuous expansion trend due to the use of a fixed power increase rate. During this stage, by maintaining a fixed power increase rate, the expansion range is ensured to remain uniform and stable. During the power supply process, when the product temperature rises within the range of strong endothermic reactions such as bond breaking and heteroatom expulsion, the length of the electrode column exhibits a periodic trend of slowing growth or stagnation-contraction-growth-contraction. During this stage, by slowing down the rate of power increase, its periodic trend is ensured, maintaining a uniform and stable range of change. During the power supply process, when the product temperature rises within the graphitization complete crystal range, the length of the electrode column tends to shrink. During this stage, the rate of power increase is adjusted to ensure the shrinkage range and maintain a uniform and stable change range. VI. Cooling process: 1. Power-off pressure maintenance: After power is restored, the power transmission trolley is replaced by a pre-set pusher to maintain pressure for 24 hours. At the same time, the gas collection hood covers the furnace surface for 24 hours to collect the escaping exhaust gas, which is then discharged after desulfurization and dust removal. Observe in real time until no more flue gas escapes from the furnace top, then remove the gas collection hood and allow the furnace to cool naturally due to thermal inertia. 2. Controlled Cooling: After removing the gas collection hood, a temperature measuring device is installed near the furnace wall and at the center point along the length of the electrode column to control furnace heat dissipation. Water spray cooling is adopted. Calculations show that spraying 27 kg of mist water evenly along a 300 mm wide area on both sides of the electrode column every 4 hours can form a stable thermal gradient, controlling the cooling rate to ≤20°C / h. This fully releases the thermal stress in the brittle region of the product and prevents cooling cracks. Compared with traditional rapid cooling methods, the yield of parts produced by controlled cooling is 98.5% and 99.4%, respectively, a difference of approximately 1%. 3. Pre-furnace confirmation: The furnace core temperature must be reduced to ≤420°C; VII. Conditions required for the product to be ready for baking 1. Temperature conditions: The maximum temperature of the furnace core is ≤420°C. After the electrodes are removed by a special gripper, they are placed on a cooling platform made of refractory material and allowed to cool naturally to room temperature. 2. Quality prediction conditions: Visual inspection: The electrode surface has a uniform silver-gray metallic luster, with no visible longitudinal cracks, surface oxidation, or electrolytic corrosion. Pay special attention to checking for stress cracks at the connection between ends A and B. Initial performance test: Perform on-site resistivity testing on the electrodes exiting the furnace; the value should be stable at 10.0 μΩ·m.

[0026] Example 2: Implementation Case of Robust Constant Current Power Transmission Technology Example of the production plan and implementation of furnace #5 in Graphitization Workshop 2 1. Product specifications, quantity (pieces), and weight (t): Diameter Φ1300 / 1000×2800mm / piece × 14 pieces / furnace, total weight 83.268t. See attached statistics for details. Figure 3 ; 2. Furnace core dimensions: 13266.5cm 2 3. Furnace loading operation: 3.1 The thickness of the insulation layer laid from the bottom of the furnace is 850mm, with a particle size of 0-2mm and a bulk density of 0.9g / cm³. 3 It replaces granulated carbon black as a heat insulation layer to protect the furnace bottom structure. The upper surface of the heat insulation layer must be smoothed, and when personnel are operating inside the furnace, a construction-grade water-based formwork should be laid to reduce uneven thickness of the heat insulation layer caused by personnel movement; 3.2. With the center normal of the width of the furnace head electrode group as the center line, apply a 1700mm wide, 200mm thick, 5-9mm particle size resistance material to the upper surface of the insulation layer. The purpose is to utilize its high contact resistance to ensure that the current does not deviate. 3.3. Align the calcined electrodes along the normal direction of the center of the positive and negative electrode assembly at the furnace head, and connect the 14 electrodes in series to form an electrode column. Ensure that the center lines of the electrode column and the furnace head electrode assembly are aligned, and no misalignment is allowed. Fill the gaps between the electrodes with flexible graphite gaskets. Then, use our pre-pressurization device to pre-pressurize the electrodes, ensuring full contact between the flexible graphite gaskets and the electrode end faces, and maintain pressure. Use a column assembly method of "non-uniform diameter large end to small end". 3.4 After the electrode posts are installed and checked for flatness and straightness, while maintaining pressure with the pre-pressurization device, place H-shaped frame plate grooves on both sides of the electrode post along its diameter. The grooves should be 200mm wide and 1600mm high, with the bottom perpendicular to the edge of the resistance material from step 3.2. Use a suction crane to fill the area directly above the electrode posts with 5-9mm resistance material, covering it with a thickness of 150mm. The width on both sides of the electrode posts should be no less than 200mm, and the height should be the same as the 150mm thickness covering the area directly above the electrode posts. The resistance material coverage is now complete. Then, use the suction crane to symmetrically add 0-2mm insulation material, ensuring the width from the edge of the frame plate groove to the furnace wall is ≥650mm. Our company uses a width of 700mm per side, with the height the same as the resistance material on both sides of the electrode posts. At this point, release the pressure from the pre-pressurization device and remove the frame plate grooves using a crane. When working on the furnace surface, apply a water-repellent template to prevent damage to the boundary layer between the resistance material and the insulation material. 3.5. Based on step 3.4, starting from the center of the electrode column diameter and along the length of the electrode column, 1m away from the inner conductive wall of the furnace head electrode, erect a steel chimney every 2.5m. The chimney diameter is 250mm and the height is 750mm. The chimney is filled with filler material with a particle size of 8-25mm. After filling, cover the chimney opening. 3.6. Based on 3.5, use a suction crane to lay 0-2mm insulation material around the chimney. The top insulation material should be trapezoidal, with the upper base length centered on the chimney diameter and the width extending to both sides being 850mm, and the lower base length being equal to the furnace width of 3100mm. The trapezoidal height should be 850mm. Then, use the crane to lift the steel chimney out. The furnace loading is now complete. 4. Power supply: 4.1 Power Supply Curve: Before power supply, the furnace head electrode assembly is cooled by water. Power supply is performed according to the power supply curve. The initial power is 2500kW. After 15 minutes of power supply, the actual furnace resistance and theoretical furnace resistance are calibrated. The error is ≤±0.5%. If the error exceeds the standard, the power supply is stopped, and the contact quality between the short network, the power transmission trolley, and the furnace head electrode assembly is checked. If the error does not exceed the standard, power supply continues. 3000-4400KW, rising power of 100kW / h, maintenance time of 14 hours. Corresponding current range 49.4-61.2KA. Electricity consumption during the period: 52500kWh; 4400-5000kW, rising power is 200kW / h. Duration is 3 hours. Corresponding current range is 61.2-67.32KA. Electricity consumption during this period is 14100kWh. 5000-5300kW, with a power increase of 100kW / h. Duration: 3 hours. Corresponding current range: 67.32-72.15KA. Electricity consumption during this period: 15450kWh. 5300-6100kW, with a power increase of 200kW / h. Duration: 4 hours. Corresponding current range: 72.15-73.3KA. Electricity consumption during this period: 22800kWh. 6100-6300kW, rising power is 400kW / h. Duration: 0.5 hours. Corresponding current range: 73.3-74.0KA. Electricity consumption during this period: 6200kWh. 6300-7000kW, rising power is 1400kW / h. Duration: 0.5 hours. Corresponding current range: 74.0-74.6KA. Energy consumption during this period: 6650kWh. 7000-10000kW, rising power is 600kW / h. Duration: 0.5 hours. Corresponding current range: 74.6-76.6KA. Electricity consumption during this period: 42500kWh. 10000-11000kW, rising power is 2000kW / h. Duration: 0.5 hours. Corresponding current range: 76.6-79.1KA. Electricity consumption during this period: 10500kWh. 11000-13000kW, rising power is 4000kW / h. Duration: 0.5 hours. Corresponding current range: 79.1-84.05KA. Electricity consumption during this period: 12000kWh. 13000-15000kW, with a power rise of 2000kW / h. Duration: 1 hour. Corresponding current range: 84.05-90.0KA. Electricity consumption during this period: 14000kWh. 15000-16000kW, with a power rise of 2000kW / h. Duration: 0.5 hours. Corresponding current range: 90.0-92.0KA. Electricity consumption during this period: 15500kWh. 16000-24000kW, with a power rise of 16000kW / h. Duration: 0.5 hours. Corresponding current range: 92.0-109.8KA. Electricity consumption during this period: 20000kWh. 24000-20000kW, power reduction of 8000kW / h. Duration: 0.5 hours. Corresponding current range: 109.8-93.5KA. Electricity consumption during this period: 22000kWh. 20000KW - Power outage continues to reduce power to 16000kw, transformer disconnection, power outage duration 0.25 hours; Cumulative electricity consumption: 254,187.5 kWh, equivalent to a unit consumption of 3,052.643 kWh / t; Total power supply duration: 34 hours.

[0027] Conclusion: The average resistivity of the product after graphitization was 10.07 μΩ·m, with a maximum of 11.9 and a minimum of 8.1, which is within acceptable limits. The resistivity of the product obtained using this method is approximately 5 μΩ·m lower than that of the same specification Acheson graphitized product. The product yield was 100%. A horizontal comparison of this method and the same specification product using the Acheson graphitization process shows that if the resistivity reaches 10.07 μΩ·m, the power consumption per ton for the Acheson graphitization process is approximately 3100 kWh / t.

[0028] Specifically, in practical applications, this invention involves precision machining of the electrode end faces of the roasted product; strict matching of electrodes within the same furnace based on resistivity to ensure a range difference of less than 5 μΩ·m; and furnace resistance matching for two furnaces connected in parallel. By employing a series connection method with the large end to the small end, multiple electrodes are connected in series to form a column using a specially designed flexible graphite pad, and a constant axial pressure of no less than 60 tons is immediately applied and maintained throughout the subsequent process. A high-precision constant current DC power supply is used, implementing a three-stage power delivery curve, with constant current as the core control mode throughout. Non-equal diameter series connection and constant voltage ensure uniform current distribution, contact reliability, and robustness. Constant current and displacement feedback precisely control the most fatal thermal stress cracks in extra-large diameter electrodes from the source, increasing the yield from the industry standard of -95% to ≥98%, with a resistivity as low as approximately 10μΩ·m, exhibiting excellent and stable performance. The combination of direct heating in the internal furnace and optimized power supply curve shortens the power supply cycle to 30-36 hours and reduces the power consumption per ton to 3000-3500kWh, achieving energy savings of over 20% compared to traditional processes and significantly improving production efficiency. The entire process, from furnace loading and resistance matching to constant current power supply and spray cooling, achieves parameterized and monitorable closed-loop control, making it particularly suitable for the large-scale and stable production of extra-large diameter electrodes.

[0029] Those skilled in the art will recognize that the modules and method steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0030] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the devices, equipment, and modules described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0031] Furthermore, it should be noted that the combination of the various technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0032] It should be noted that the above examples are merely specific embodiments of the present invention, and the present invention is obviously not limited to the above embodiments, with many similar variations. All modifications that can be directly derived or conceived by those skilled in the art from the content disclosed in this invention should fall within the protection scope of this invention.

[0033] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A graphitization process for an ultra-large diameter graphite electrode, characterized in that, The specific steps include the following: S1. Furnace preparation and resistance matching: The electrode end faces of the roasted products are precisely machined and matched according to resistivity to ensure that the resistivity difference of electrodes in the same furnace is less than 5μΩ·m. S2. Non-equal diameter end pressure series loading: Multiple non-equal diameter roasted electrodes are connected in series through a flexible graphite pad to form an electrode column, and a constant axial pressure of not less than 60 tons is applied to the entire electrode column and maintained throughout the process. S3. Robust constant current power supply: Power supply is carried out using a constant current control mode. The power supply process includes a rapid preheating period, a pyrolysis and reshaping period, and a graphitization improvement period, which are carried out in sequence. During the pyrolysis and reshaping period, the heating rate is controlled within the range of 30-50℃ / h. Furthermore, the axial displacement of the electrode post is monitored in real time during the power supply process, and the current control parameters are dynamically fine-tuned based on the displacement change trend to keep the displacement change stable. S4. Coordinated and controllable cooling: After power supply is completed, the axial pressure is maintained and the exhaust gas is collected. Then, controllable cooling is carried out. By spraying mist water onto the furnace body, the furnace core cooling rate is controlled at ≤20℃ / h until the furnace core temperature drops below 420℃ before being unloaded.

2. The graphitization process for extra-large diameter graphite electrodes according to claim 1, characterized in that: In step S1, furnace resistance matching is performed on the electrode posts of the two furnaces that are connected in parallel to ensure that the total furnace resistance of the two furnaces is equal.

3. The graphitization process for extra-large diameter graphite electrodes according to claim 1, characterized in that: The series connection method in step S2 is large end to small end series connection; the specifications of the flexible graphite pad are matched with the size of the non-equal diameter ends of the electrode.

4. The graphitization process for extra-large diameter graphite electrodes according to claim 1, characterized in that: The rapid preheating period in step S3 corresponds to the temperature from room temperature to 900°C, during which the current rises rapidly; the pyrolysis and reshaping period corresponds to the temperature from 900°C to 1800°C, during which the current rises gradually; and the graphitization perfection period corresponds to the temperature above 1800°C, during which the current first remains constant and then slowly decreases.

5. The graphitization process for extra-large diameter graphite electrodes according to claim 1, characterized in that: In step S3, the dynamic fine-tuning of the current control parameters based on the displacement change trend refers to automatically reducing the current rise rate when an abnormally rapid contraction trend is detected in the electrode column during the pyrolysis remodeling period.

6. The graphitization process for extra-large diameter graphite electrodes according to claim 3, characterized in that: The controllable cooling in step S4 is intermittent quantitative spraying, specifically, every 4 hours, a certain amount of mist water is sprayed into specific areas on both sides along the length of the electrode column.

7. The graphitization process for extra-large diameter graphite electrodes according to claim 6, characterized in that: The measured amount is approximately 27 kg of water sprayed each time, and the flexible graphite pad is kept dry before use.

8. The graphitization process for extra-large diameter graphite electrodes according to claim 6, characterized in that: The space between the electrode post and the furnace wall is filled with resistive material and heat-insulating material, and exhaust holes are provided at intervals along the length of the electrode post.

9. The graphitization process for extra-large diameter graphite electrodes according to claim 1, characterized in that: The graphitization process requires connection to an electrical equipment system, which includes: The DC power supply subsystem has a rated DC output current ≥250kA and a constant current automatic control function with a current control accuracy ≤±1%. The hydraulic pressurization subsystem is configured to apply a constant axial pressure of not less than 60 tons to the series-connected electrode columns, and has a constant pressure control function that ensures pressure fluctuations of ≤±5% throughout the power transmission process. The cooling subsystem employs a closed-loop pure water cooling system to cool the key components of the DC power supply subsystem and the hydraulic pressurization subsystem.

10. The graphitization process for the extra-large diameter graphite electrode according to claim 9, characterized in that: The power equipment system also includes an intelligent control terminal, which includes: The central control module has a pre-stored three-stage curve program for robust constant current power transmission. The displacement feedback module includes a sensor for real-time monitoring of the axial displacement of the electrode post and is communicatively connected to the central control module to feed back displacement change data to the central control module. The central control module is configured to: receive data from the displacement feedback module and, based on a preset displacement stability model, dynamically adjust the current control parameters output to the DC power supply subsystem during the power transmission process. The spray control module, connected to the central control module, is configured to control the spray device to perform the intermittent quantitative spraying according to instructions during the cooling phase.

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