Superconducting electromagnetic induction heating method for continuous graphitization furnace

Abstract

The invention discloses a superconducting electromagnetic induction heating method for a continuous graphitization furnace, which comprises the following steps of: applying a high-frequency high-field alternating magnetic field under the cooling of liquid nitrogen by adopting a YBCO strip barrel type superconducting magnet, instantly generating eddy current in a carbonaceous material, heating to 3,000 DEG C in a second level to complete graphitization, and controlling lattice orientation and quenching solidification by combining a gradient magnetic field. The high-purity and high-conductivity graphite is obtained. The energy consumption of each ton of products is reduced to about 1000-200 kilowatt-hours, the temperature rise time is shortened by two orders of magnitude, and the method is suitable for continuous and efficient production.

Description

Technical Field

[0001] This invention belongs to the field of graphitization technology in the carbon-based materials industry, and particularly relates to a superconducting electromagnetic induction heating method for a continuous graphitization furnace. Background Technology

[0002] Traditional Atchison graphitization furnaces employ various heating methods, including AC heating, DC heating, ambient temperature electromagnetic heating, continuous (dominantly electromagnetic) heating, and microwave heating. Taking DC heating as an example, after 50-70 hours of continuous power supply, electrical energy is converted into heat energy through the Joule heating effect. Graphitization is ultimately achieved when the furnace core temperature reaches approximately 3000°C. Research and practice have shown that the transformation of carbon materials into graphite occurs almost instantaneously; that is, when the temperature reaches approximately 3000°C, amorphous carbon undergoes instantaneous lattice recombination to transform into graphite. Therefore, the heating process from the start of power supply to the 2800°C range in traditional graphitization furnaces consumes a lot of electricity. Studies have shown that only 30% of the electrical energy in traditional graphitization furnaces is effectively utilized, with the remaining 70% being wasted.

[0003] Traditional graphitization furnace heating methods use direct current and contact heating, which rely on Joule heating, resulting in high energy consumption (>5000kWh / t) and low energy utilization. It takes 50-70 hours or even longer to supply power when heating to 3000℃. The product quality is affected by uneven temperature distribution, leading to uneven graphitization.

[0004] With the rapid advancement of new materials and technologies, the development of superconducting materials has shifted from low-temperature to high-temperature applications in recent years. For example, copper oxide high-temperature superconductors have… Bi2Sr2Ca2Cu3O 10 (BSCCO-2223) These copper oxide high-temperature superconductors have maintained their transition temperatures (Tc) between 77K and 138K under ambient pressure. Breaking the liquid nitrogen temperature (77K, -196℃) is a major milestone in the application of superconducting materials, greatly reducing the application threshold.

[0005] Superconducting magnets can establish a strong magnetic field faster and more efficiently than traditional electromagnets. Utilizing the zero-resistance characteristic, they can rapidly inject large currents through high voltage or gradually accumulate currents through flux pumps. Through flux pumps or superconducting switch (PCS) technology, current can flow permanently and without loss in a closed superconducting circuit after excitation is completed, thereby instantly locking and maintaining a strong and stable magnetic field for a long time. This is the unparalleled advantage of superconducting magnets. Summary of the Invention

[0006] This invention discloses a superconducting electromagnetic induction heating method for a continuous graphitization furnace, aiming to reduce the energy consumption of the graphitization furnace.

[0007] To achieve this objective, the present invention adopts the following technical solution: A superconducting electromagnetic induction heating method for a continuous graphitization furnace includes the following steps: S1 places the pre-carbonized material in a nitrogen-protected silicon carbide roller conveyor system with an oxygen content of <10ppm; S2 injects an alternating current with a frequency of 10–50 kHz and a peak magnetic induction intensity of 3–10 T into a cylindrical high-temperature superconducting magnet, inducing a magnetic flux density >10 T within the material. 7 Eddy current density in A / m²; S3 utilizes the eddy current to raise the temperature of the material from room temperature to above 3000°C within 2–3 seconds, thereby completing graphitization; S4 controls the lattice ordering direction through an axial gradient magnetic field, and adjusts the magnetic field strength in real time by infrared thermometry, with an error of ±5℃. After the S5 material was removed from the magnetic field region, it was rapidly cooled in an inert gas environment to obtain a graphitization degree > 99.2% and an electrical conductivity > 10. 5 Graphite products of S / m.

[0008] Preferably, the cylindrical high-temperature superconducting magnet is wound with YBCO or BSCCO-2223 tape, and the cooling system adopts a two-stage GM refrigerator and a liquid nitrogen circulation loop to maintain 77±0.5K.

[0009] Preferably, the silicon carbide roller conveyor system is continuous, enabling continuous feeding, heating, cooling, and discharging of materials.

[0010] Preferably, the energy consumption per ton of product is ≤1200kWh.

[0011] Preferably, the heating rate is 800–1200 °C / s.

[0012] Preferably, the peak magnetic field flows permanently and without damage in a closed superconducting circuit through a flux pump or a superconducting switch, thereby achieving instantaneous locking and long-term stability of the magnetic field.

[0013] Preferably, the axial gradient magnetic field is continuously adjustable along the roller conveyor axis, with a field strength gradient of 0.5–2 T / m, and is used to guide the preferred orientation of the c-axis of the graphite microcrystals.

[0014] Preferably, the infrared temperature measuring point is located at the magnetic field outlet end, and the temperature measurement signal is fed back to the high-frequency power controller to realize closed-loop adjustment of the magnetic field strength.

[0015] Preferably, the inert gas quenching is performed by nitrogen or argon injection, with a cooling rate ≥500℃ / s, so as to quickly fix the graphite interlayer spacing.

[0016] Preferably, the pre-carbonized material is petroleum coke, needle coke or carbon black, with a particle size of 0.2–2 mm and a carbon content of ≥97 wt%.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Maximum temperature: Traditional graphitization furnaces can heat to 2800-3000℃, while superconducting electromagnetic induction can heat to >3200℃; 2. Heating rate: Traditional graphitization furnaces require 50℃ / h, while superconducting electromagnetic induction heating can reach 800℃-1200℃ / s; 3. Energy consumption per ton of product: Traditional graphitization furnaces consume approximately 5000-6000 kWh / t, while those using superconducting electromagnetic induction consume only 1200 kWh / t, less than 1 / 4 of the former. 4. Graphitization degree of products: The graphitization degree of products from traditional graphitization furnaces is about 93-95%, while the graphitization degree of products using superconducting electromagnetic induction can reach >99.2%. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the electromagnetic ultra-high temperature generation principle of the present invention. Figure 2 This is a flowchart of the continuous graphitization production process of the present invention; Figure 3 This is a schematic diagram of the device of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0020] A superconducting electromagnetic induction heating method for a continuous graphitization furnace includes the following steps: S1 places the pre-carbonized material in a nitrogen-protected silicon carbide roller conveyor system with an oxygen content of <10ppm; S2 injects an alternating current with a frequency of 10–50 kHz and a peak magnetic induction intensity of 3–10 T into a cylindrical high-temperature superconducting magnet, inducing a magnetic flux density >10 T within the material. 7 Eddy current density in A / m²; S3 uses eddy currents to raise the temperature of the material from room temperature to above 3000℃ within 2–3 seconds, thus completing the graphitization. S4 controls the lattice ordering direction through an axial gradient magnetic field, and adjusts the magnetic field strength in real time by infrared thermometry, with an error of ±5℃. After the S5 material was removed from the magnetic field region, it was rapidly cooled in an inert gas environment to obtain a graphitization degree > 99.2% and an electrical conductivity > 10. 5 Graphite products of S / m.

[0021] Graphitization can be completed in one step using non-contact eddy current heating in 2–3 seconds, completely eliminating the need for traditional 50–70 hours of resistance Joule heating. Energy consumption per ton is reduced from 5000 kWh to below 1200 kWh, while achieving a graphitization degree of >99.2%.

[0022] In one optional embodiment, the cylindrical high-temperature superconducting magnet is wound with YBCO or BSCCO-2223 tape, and the cooling system adopts a two-stage GM refrigerator and a liquid nitrogen circulation loop to maintain 77±0.5K.

[0023] Operating at a liquid nitrogen temperature of 77K, it eliminates the need for expensive liquid helium, reducing operating costs to only 1 / 5 of traditional cryogenic superconductors; its zero-resistance characteristic allows it to withstand strong magnetic fields of 3–10T without copper loss, ensuring instantaneous high power output of 10 7 A / m² level eddy currents provide a sufficient magnetomotive force source; The two-stage GM refrigeration unit operates in a closed loop, eliminating the risk of cryogenic liquid storage and transportation on-site, making it suitable for continuous industrial operations.

[0024] In one optional embodiment, the silicon carbide roller conveyor system is continuous, enabling continuous material feeding, heating, cooling, and discharging.

[0025] The silicon carbide roller conveyor does not soften or contaminate the product at 3000℃. It has high resistivity and hardly absorbs eddy currents, avoiding additional heating and energy waste. The roller conveyor can continuously convey materials, achieve graphitization at 3000℃, rapid cooling, and discharge in one line. The daily production capacity of a single unit is ≥20t, which is more than 5 times that of the traditional Acheson furnace. It is sealed with nitrogen positive pressure and has low oxygen <10ppm to prevent the carbon material from oxidizing and burning at high temperature. The ash content of the finished product is <0.05%.

[0026] In one alternative implementation, the energy consumption per ton of product is ≤1200kWh.

[0027] Compared to the traditional 5000–6000 kWh / t, this directly saves ≥76%. Based on a scale of 100,000 tons / year, the annual electricity saving is approximately 3.8 × 10⁻⁶ kWh / t. 8 kWh, equivalent to a reduction of approximately 300,000 tons of CO2 emissions.

[0028] In one alternative implementation, the heating rate is 800–1200 °C / s.

[0029] The second-level heating allows lattice recombination and graphitization to be completed before thermal stress is relaxed, resulting in larger crystallite size, smaller interlayer spacing, and increased conductivity by 10–20%. The extremely rapid supercooling inhibits secondary crystallization, reduces grain boundary defects, and increases flexural strength by 10–15%. High-speed heating shortens the high-temperature exposure time, and the amount of refractory material used in the equipment and heat loss decrease simultaneously, further reducing unit energy consumption.

[0030] In one alternative implementation, the peak magnetic field flows permanently and without damage in a closed superconducting circuit via a flux pump or a superconducting switch, achieving instantaneous locking and long-term stability of the magnetic field.

[0031] Excitation is completed within 0.1 seconds and the magnetic field is locked with zero loss. It can maintain 5T for several hours after a power outage. Power grid flicker / short-term power outages do not affect production. The system availability rate is >99%. It eliminates the excitation loss of copper coils in continuous power supply, resulting in additional power savings of 3-5%. It has no mechanical contacts and a lifespan of >10 years. 6 This technology is maintenance-free and improves the continuous operation capability of the production line.

[0032] In one optional embodiment, the axial gradient magnetic field is continuously adjustable along the roller conveyor axis, with a field strength gradient of 0.5–2 T / m, used to guide the preferred c-axis orientation of graphite microcrystals. The gradient field applies a directional magnetic torque to the graphite microcrystals, causing the c-axis to align preferentially along the heat flow direction, increasing the 004 / 110 peak area ratio by more than 8%, reducing the electrical / thermal anisotropy of the electrode material, and improving charge / discharge rate performance. The orientation degree can be controlled online by adjusting the gradient value, eliminating the need for post-processing. Both isotropic and highly oriented specifications can be produced in the same batch, flexibly matching different markets such as lithium battery anodes and isostatic graphite.

[0033] In one optional implementation, the infrared temperature measurement point is located at the magnetic field outlet, and the temperature measurement signal is fed back to the high-frequency power controller to achieve closed-loop regulation of the magnetic field strength. Through 2kHz high-speed sampling and PID feedback, the problems of large temperature gradients and uneven product distribution in traditional furnaces are completely solved. The magnetic field-power linkage response time is less than 5ms, which can suppress hot spots and overheating in real time, and improve the finished product qualification rate from 92% to over 99%.

[0034] In one optional embodiment, the inert gas quenching employs nitrogen or argon injection at a cooling rate ≥500℃ / s, rapidly fixing the graphite interlayer spacing. High-speed cooling freezes the high-temperature graphite structure, inhibiting interlayer recombination. 002 The conductivity is reduced to 0.3356nm, and the electrical conductivity is increased by 10-15%. Spray cooling replaces traditional water quenching / oil quenching, resulting in no wastewater, no thermal shock cracks, and high particle integrity. The heat from the cooling section is carried away by the inert gas and recovered by the heat exchanger, which can preheat the feed and further improve the system's thermal efficiency by 5-8%.

[0035] In one optional embodiment, the pre-carbonized material is petroleum coke, needle coke, or carbon black, with a particle size of 0.2–2 mm and a carbon content of ≥97 wt%.

[0036] This invention employs a high-temperature superconducting magnet YBCO / BSCCO-2223 tape winding method, based on the eddy current heating core formula Pv= Pv is the heat generation power density (W / m3, which determines the heating rate), f is the magnetic field frequency (Hz, the higher the frequency, the stronger the surface heating), and Bp is the peak magnetic flux density (Tesla, superconducting magnets can reach 5-10T). The penetration depth is ρ (m), and the resistivity of the material is ρ (Ω·m). This is a non-contact heating method.

[0037] Example 1 Please see Figures 1-3 Cylindrical high-temperature superconducting magnet: wound with YBCO tape, inner diameter 200mm, length 800mm, cooled by liquid nitrogen at 77K.

[0038] Magnetic field parameters: frequency 20kHz, peak value 5T, axial gradient 1T / m.

[0039] Conveying: Nitrogen-protected silicon carbide roller conveyor, speed 0.5m / min.

[0040] The material used is petroleum coke with a particle size of 0.5-1mm, a carbon content of 98%, and a bulk density of 0.8g / cm³.

[0041] Oxygen content controlled to ≤8ppm, injected with 20kHz / 5T AC current, eddy current density 1.2×10 7 A / m², the center temperature rises to 3020℃ within 2.4s, the infrared closed-loop adjustment error is ±4℃, and the argon gas quenching is 600℃ / s.

[0042] Actual measurements show an energy consumption of 1150 kWh per ton, a graphitization degree of 99.3%, and an electrical conductivity of 1.1 × 10⁻⁶ kWh per ton. 5 S / m.

[0043] Example 2 The only difference from Example 1 is that: A superconducting switch was used to lock the coil current to 2.5kA within 0.1s, and the magnetic field of 5T was maintained for 10 minutes without decay.

[0044] Actual measurements showed that with a heating rate of 1000℃ / s, the total energy consumption was reduced to 1100kWh / t, and the grain orientation was improved by 8%; XRD004 / 110 peak area ratio.

[0045] Example 3 The only difference from Example 1 is that: The axial gradient is set to 1.8T / m.

[0046] The roller conveyor speed is 0.3 m / min, and the residence time in the high-temperature zone is extended to 3 seconds.

[0047] The product was tested by EBSD and the average angle between the c-axis and the roller direction was 12°, with the bending strength improved by 15%.

[0048] Example 4 The only difference from Example 1 is that: The infrared temperature measurement point is set 50mm from the magnetic field outlet, with a sampling frequency of 2kHz. The PID controller adjusts the high-frequency power supply in real time, and the magnetic field strength is finely adjusted within the range of 4.8-5.2T; Actual measurements showed that the standard deviation of the temperature of the entire batch of materials was ≤3℃, and the fluctuation of graphitization degree was <0.2%.

[0049] Example 5 The only difference from Example 1 is that: The quench section is equipped with 6 rows of 1mm nozzles, with an argon flow rate of 120Nm. 3 / h, apparent airflow velocity 120m / s; Cooling rate 700℃ / s, interlayer spacing d 002 The nanometer diameter decreased from 0.3362 nm to 0.3356 nm, and the conductivity increased to 1.3 × 10⁻⁶. 5 S / m.

[0050] Example 6 The only difference from Example 1 is that: The coke used has a needle-like particle size of 1.5-2 mm and a carbon content of 97.5%. The frequency was reduced to 12kHz to increase the skin depth, while the eddy current density remained at 1.0×10⁻⁶. 7 A / m²; It can reach 3050℃ in 2.8s, consumes 1180kWh per ton of energy, and has a graphitization degree of 99.4%, making it suitable for preparing ultra-high power electrode aggregates.

[0051] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A superconducting electromagnetic induction heating method for a continuous graphitization furnace, characterized in that, Includes the following steps: S1 places the pre-carbonized material in a nitrogen-protected silicon carbide roller conveyor system with an oxygen content of <10ppm; S2 injects an alternating current with a frequency of 10–50 kHz and a peak magnetic induction intensity of 3–10 T into a cylindrical high-temperature superconducting magnet, inducing a magnetic flux density >10 T within the material. 7 Eddy current density in A / m²; S3 utilizes the eddy current to raise the temperature of the material from room temperature to above 3000°C within 2–3 seconds, thereby completing graphitization; S4 controls the lattice ordering direction through an axial gradient magnetic field, and adjusts the magnetic field strength in real time by infrared thermometry, with an error of ±5℃. After the S5 material was removed from the magnetic field region, it was rapidly cooled in an inert gas environment to obtain a graphitization degree > 99.2% and an electrical conductivity > 10. 5 Graphite products of S / m.

2. The method according to claim 1, wherein the cylindrical high-temperature superconducting magnet is wound with YBCO or BSCCO-2223 tape, and the cooling system adopts a two-stage GM refrigerator and a liquid nitrogen circulation loop to maintain 77±0.5K.

3. The method according to claim 1 or 2, wherein the silicon carbide roller conveyor system is continuous, realizing continuous material feeding, heating, cooling and discharging.

4. The method according to claim 1, wherein the energy consumption per ton of product is ≤1200kWh.

5. The method according to claim 1, wherein the heating rate is 800–1200 °C / s.

6. The method according to claim 1, wherein the peak magnetic field flows permanently and without loss in a closed superconducting circuit through a flux pump or a superconducting switch, thereby achieving instantaneous locking and long-term stability of the magnetic field.

7. The method according to claim 1, wherein the axial gradient magnetic field is continuously adjustable along the roller axis direction, with a field strength gradient of 0.5–2 T / m, and is used to guide the preferred orientation of the c-axis of graphite microcrystals.

8. The method according to claim 1, wherein the infrared temperature measuring point is located at the magnetic field outlet end, and the temperature measuring signal is fed back to the high-frequency power controller to realize closed-loop adjustment of the magnetic field strength.

9. The method according to claim 1, wherein the inert gas quenching is performed by nitrogen or argon injection at a cooling rate ≥500℃ / s, thereby rapidly fixing the graphite interlayer spacing.

10. The method according to claim 1, wherein the pre-carbonized material is petroleum coke, needle coke or carbon black, with a particle size of 0.2–2 mm and a carbon content ≥97 wt%.

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