Three-stage composite kiln for preparing spherical alumina

Abstract

The application discloses a three-section composite kiln for preparing spherical alumina, which comprises an infrared preheating section, a microwave medium-high temperature phase conversion section and a plasma heating section which are sequentially and tightly connected; the microwave medium-high temperature phase conversion section is connected with the infrared preheating section and the plasma heating section through a first microwave energy suppressor, and the microwave medium-high temperature phase conversion section is connected with the plasma heating section through a second microwave energy suppressor, so as to protect the safety of the operators of the equipment; the infrared preheating section, the microwave medium-high temperature phase conversion section and the plasma heating section are sequentially connected to form the main body of the three-section composite kiln for preparing spherical alumina; the infrared preheating section is used as a pretreatment section and is used for drying and dehydrating alumina raw materials; the microwave medium-high temperature phase conversion section is used as a crystal phase conversion section and is used for converting alumina from a gamma phase to an alpha phase through microwave radiation; and the plasma heating section is used as a spherical shaping section and is used for spherical shaping of molten alumina particles through gas suspension turbulent flow.

Description

Technical Field

[0001] This invention belongs to the technical field of inorganic non-metallic material preparation equipment, specifically relating to a three-stage continuous spherical alumina preparation kiln system, which is particularly suitable for continuous production to achieve alumina crystal phase transformation and spherical shaping. Background Technology

[0002] Alumina (Al2O3) is a high-performance inorganic non-metallic material with high melting point, high hardness, excellent thermal stability, and insulation properties. It is widely used in electronic packaging substrates, high-temperature structural ceramics, catalyst supports, and thermally conductive fillers. Among them, spherical alumina, due to its high packing density, low coefficient of friction, and excellent flowability, has become a core material for high-end applications such as heat dissipation in 5G communication modules and coating of power battery separators.

[0003] Traditional processes for preparing spherical alumina typically employ gas-fired rotary kilns, which suffer from problems such as lengthy processes, insufficient phase transformation, poor sphericity, high energy consumption, and significant energy waste. Furthermore, traditional heat conduction heating methods exhibit high thermal inertia and uneven temperature fields, making it difficult to simultaneously optimize sphericity and phase purity. Therefore, there is an urgent need for a highly efficient, energy-saving, and continuously operating spherical alumina preparation equipment. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a three-section composite kiln for preparing spherical alumina, employing the following technical solution:

[0005] A three-section composite kiln for preparing spherical alumina includes an infrared preheating section, a microwave medium-high temperature phase inversion section, and a plasma heating section that are sequentially sealed and connected.

[0006] The microwave high-temperature phase transition section and the infrared preheating section are connected by a first microwave energy suppressor, and the microwave high-temperature phase transition section and the plasma heating section are connected by a second microwave energy suppressor to protect the safety of the equipment operators; the infrared preheating section, the microwave high-temperature phase transition section and the plasma heating section connected in sequence form the main body of a three-section composite kiln for preparing spherical alumina;

[0007] The infrared preheating section serves as a pretreatment section for drying and dehydrating alumina raw materials; the microwave high-temperature phase transformation section serves as a crystal phase transformation section, using microwave radiation to transform alumina from the γ phase to the α phase; and the plasma heating section serves as a spherical shaping section, using an air-suspended turbulent flow field to spherically shape molten alumina particles.

[0008] The air-suspended turbulent field is formed as follows: the plasma torch at the bottom of the plasma heating section generates a high-temperature, high-speed airflow, which enters the shaping cavity of the spherical shaping section from bottom to top, forming a gas flow region with rotational and turbulent characteristics in the upper space of the shaping cavity, thereby forming an air-suspended turbulent field; the molten alumina particles entering the gas flow region remain suspended and continuously tumble under the action of the airflow, and gradually shrink and form spherical particles under the action of surface tension.

[0009] Furthermore, the infrared preheating section includes an infrared preheating section furnace body, a K-type thermocouple, and a high-purity alumina crucible; an insulating sleeve is fixedly fitted outside the infrared preheating section furnace body; a distributed infrared heat source is installed inside the insulating sleeve to uniformly heat the infrared preheating section furnace body; the K-type thermocouple is installed inside the furnace chamber of the infrared preheating section furnace body and is positioned corresponding to the material at the bottom of the furnace to monitor the temperature of the furnace chamber; the high-purity alumina crucible is installed inside the furnace chamber; the outlet of the infrared preheating section furnace body is connected to the microwave high-temperature phase transition section through the first microwave energy suppressor.

[0010] Furthermore, the microwave high-temperature phase transition section includes a microwave oven body and a distributed magnetron system; the distributed magnetron system includes multiple magnetrons, which are arranged in an array on the outer wall of the microwave oven body and connected to the outer wall of the microwave oven body to transform alumina from the γ phase to the α phase; the inner wall of the microwave oven body is covered with a high-purity alumina ceramic liner; the inlet of the microwave oven body is connected to the outlet of the infrared preheating section through the first microwave suppressor, and the outlet is connected to the plasma heating section through the second microwave suppressor.

[0011] Furthermore, the microwave high-temperature phase transition section furnace body is equipped with armored thermocouples and an infrared temperature measurement module to measure the phase transition temperature of the alumina material in the microwave high-temperature phase transition section.

[0012] Furthermore, the plasma heating section includes a plasma heating section furnace body, a plasma generator, and a feed inlet disposed on the plasma heating section furnace body; the feed inlet is connected to the second microwave energy suppressor; the plasma generator is disposed at the bottom of the plasma heating section furnace body to heat and ionize the gas to achieve melting of alumina particles and dispersion of gas flow;

[0013] The plasma heating section furnace body is provided with an airflow cooling furnace chamber; the plasma heating section furnace body is connected to a tangential air intake system, which is used to introduce gas into the airflow cooling furnace chamber so that the alumina particles move from bottom to top; the top of the plasma heating section furnace body is connected to a cyclone separator, which is used to cool and separate the alumina particles.

[0014] Beneficial effects:

[0015] This invention provides a three-section composite kiln for preparing spherical alumina, which integrates infrared-microwave-plasma multi-heating technologies. It integrates multiple equipment required for the original materials into a single composite kiln, solving the problems of excessively long process, poor phase transformation uniformity, unstable quality, and high energy consumption in traditional processes. The design of the microwave energy suppressor ensures the safety of the equipment and operators.

[0016] Compared to gas-fired rotary kilns, this device eliminates the problems of uneven heat field and material contamination caused by natural gas heating, achieving the following results: spherical alumina with a roundness ≥ 0.96, α-phase purity ≥ 99%, and K+ and Na+ ion content ≤ 5ppm.

[0017] The high-quality spherical alumina produced by this equipment is particularly suitable for electronic packaging materials, thermally conductive fillers, and PCB thermally conductive substrate materials. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the three-section composite kiln for preparing spherical alumina according to the present invention.

[0019] The components include: 1. Infrared preheating section; 11. Heating wire; 12. Furnace chamber; 13. Insulating sleeve; 14. K-type thermocouple; 15. Proportional-integral-derivative (PID) controller; 16. High-purity alumina sagger; 17. Exhaust port; 2. Microwave medium-high temperature phase transition section; 21. Microwave resonant cavity; 22. Magnetron; 23. Infrared temperature measurement module; 3. Plasma heating section; 31. Plasma generator; 32. Tangential air intake system; 33. Cyclone separator; 4. First microwave energy suppressor; 5. Feed inlet; 6. Discharge outlet; 7. Second microwave energy suppressor. Detailed Implementation

[0020] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below.

[0021] Example 1

[0022] Reference Figure 1A three-section composite kiln for preparing spherical alumina includes an infrared preheating section 1, a microwave medium-high temperature phase inversion section 2, and a plasma heating section 3, which are sequentially sealed and connected.

[0023] The microwave high-temperature phase transition section 2 and the infrared preheating section 1 are connected by a first microwave energy suppressor 4, and the microwave high-temperature phase transition section 2 and the plasma heating section 3 are connected by a second microwave energy suppressor 7 to protect the safety of the equipment operators; the infrared preheating section 1, the microwave high-temperature phase transition section 2 and the plasma heating section 3 connected in sequence form the main body of the three-section composite kiln for preparing spherical alumina.

[0024] Among them, infrared preheating section 1 serves as a pretreatment section for drying and dehydrating alumina raw materials; microwave high-temperature phase transformation section 2 serves as a crystal phase transformation section, which transforms alumina from the γ phase to the α phase through microwave radiation, and its temperature range is determined by the grade of alumina and the types of impurity phases; plasma heating section 3 serves as a spherical shaping section, which shapes molten alumina particles into spherical shapes through an air suspension turbulent flow field.

[0025] The air-suspended turbulent field is formed as follows: the plasma torch at the bottom of the plasma heating section 3 generates a high-temperature, high-speed airflow, which enters the shaping cavity of the spherical shaping section from bottom to top, forming a gas flow region with rotational and turbulent characteristics in the upper space of the shaping cavity, thereby forming an air-suspended turbulent field; the molten alumina particles entering the gas flow region remain suspended and continuously roll under the action of the airflow, and gradually shrink and form spherical particles under the action of surface tension.

[0026] Preferably, the temperature of the infrared preheating section 1 is configured within the temperature range of 0℃ to 700℃. The alumina raw material is dried and dehydrated by infrared heating. The infrared preheating section 1 removes dissolved water and bound water from the alumina raw material, which can effectively remove moisture from the alumina raw material, inhibit boiling, and preheat the alumina raw material.

[0027] Preferably, the temperature of the microwave high-temperature phase transition section 2 is configured in the temperature range of 700℃ to 1700℃, and the alumina is driven to transform from the γ phase to the α phase by microwave radiation. The microwave high-temperature phase transition section 2 utilizes the good response capability of alumina to microwaves in the middle and high range to achieve synchronous and uniform phase transition of materials, which significantly improves the α phase conversion rate and product particle size uniformity.

[0028] Preferably, the temperature of the plasma heating section 3 is configured in the temperature range of 1700 ℃ to 2200 ℃, and the molten alumina particles are spherically shaped by the air suspension turbulent flow field; the plasma heating section 3 heats and ionizes the process gas through plasma technology, and the generated high-speed gas phase plasma heat flow causes the alumina particles to melt instantly and be blown by the high-speed airflow; the material is carried by the high-speed airflow to the low temperature zone, and rapidly solidifies into a spherical shape in free space under the action of surface tension.

[0029] The first microwave suppressor 4 and the second microwave suppressor 7 both include a dynamic sealing structure. The dynamic sealing structure includes a retractable graphite sealing ring, which is connected to the material conveying pipe between the two heating furnace bodies to form a sliding seal, ensuring that microwaves do not leak from the gaps.

[0030] Through the above technical solution, the first microwave suppressor 4 and the second microwave suppressor 7 are used to block microwave energy leakage; the temperature rise rate from the pretreatment section to the crystal phase transformation section is 5-15. ℃ / min; the temperature rise rate from the phase transformation section to the spherical shaping section is 10-20℃ / min. ℃ / min.

[0031] In this embodiment, the infrared preheating section 1 includes an infrared preheating section furnace body, a K-type thermocouple 14, and a high-purity alumina crucible 16; the infrared preheating section furnace body is provided with a feed inlet 5 and an exhaust outlet 17; an insulating sleeve 13 is fixedly fitted outside the infrared preheating section furnace body; a distributed infrared heat source is provided inside the insulating sleeve 13 to uniformly heat the infrared preheating section furnace body; the K-type thermocouple 14 is installed inside the furnace chamber 12 of the infrared preheating section furnace body and is correspondingly installed with the material at the bottom of the furnace to monitor the temperature of the furnace chamber 12 through the K-type thermocouple 14; the high-purity alumina crucible 16 is installed inside the furnace chamber 12; the outlet of the infrared preheating section furnace body is connected to the microwave high-temperature phase transition section 2 through a first microwave energy suppressor 4.

[0032] Preferably, the distributed infrared heat source is a heating wire 11, which is made of iron-chromium-aluminum alloy and generates heat when energized. The furnace chamber 12 is a space for placing the heated object and is made of refractory bricks to withstand high temperatures. Insulating material is used to isolate the heating wire 11 and the furnace body to prevent short circuits and heat loss. The electric heating kiln also includes a proportional-integral-derivative (PID) controller 15. The proportional-integral-derivative (PID) controller 15 is electrically connected to the heating wire 11 to control the heating temperature of the heating wire 11.

[0033] In this embodiment, the microwave high-temperature phase transition section 2 includes a microwave oven body and a distributed magnetron 22 system. The distributed magnetron 22 system includes multiple magnetrons 22, which are arranged in an array on the outer wall of the microwave oven body and connected to the outer wall. The magnetrons 22 cooperate with the microwave resonant cavity 21 provided inside the microwave oven body to transform alumina from the γ phase to the α phase. The inner wall of the microwave oven body is covered with a high-purity alumina ceramic liner. The inlet of the microwave oven body is connected to the outlet of the infrared preheating section through a first microwave suppressor, and the outlet is connected to the plasma heating section 3 through a second microwave suppressor 7.

[0034] In this embodiment, an armored thermocouple and an infrared temperature measurement module 23 are installed on the microwave high-temperature phase transition section furnace body to measure the phase transition temperature of the alumina material in the microwave high-temperature phase transition section 2.

[0035] In this embodiment, the plasma heating section 3 includes a plasma heating section furnace body, a plasma generator 31, and a feed inlet disposed on the plasma heating section furnace body; the feed inlet is connected to the second microwave energy suppressor 7; the plasma generator 31 is disposed at the bottom of the plasma heating section furnace body, and the plasma high-pressure nozzle of the plasma generator 31 sprays upward to heat and ionize the gas, thereby achieving melting of alumina particles and dispersion of airflow; the plasma heating section furnace body is provided with an airflow cooling furnace chamber, and the plasma high-pressure nozzle is correspondingly disposed with the airflow cooling furnace chamber to heat and ionize the gas located below the airflow cooling furnace chamber;

[0036] A tangential air intake system 32 is connected to the upper burner of the plasma heating section furnace body. The tangential air intake system 32 is used to introduce gas at a specific angle into the airflow cooling furnace chamber so that the alumina particles move from bottom to top. The angle of the introduced gas can be set according to the actual application. A cyclone separator 33 is connected to the top of the plasma heating section furnace body. The cyclone separator 33 is used to cool and separate the alumina particles.

[0037] The inlet of the plasma heating section furnace is located at the bottom, and the outlet 6 of the plasma heating section furnace is located at the top; argon or nitrogen is introduced into the tangential air intake system 32, and its airflow parameters meet the following requirements: Reynolds number Re > 4000, forming a turbulent field, so that the residence time of alumina particles is 2 to 10 seconds; a water-cooled jacket is provided on the cyclone separator 33.

[0038] The above technical solution adopts a three-stage continuous design: through the stage coupling of pretreatment electric furnace (0-700 ℃), microwave furnace (700-1700 ℃) and plasma furnace (1700-2200 ℃), the integrated continuous production of "dehydration → phase change → shaping" is realized, eliminating the energy consumption of multiple heating of materials, reducing energy consumption, and realizing the green production of spherical alumina; the final product performance of alumina raw materials meets the following requirements: α phase content (XRD analysis) ≥99%; particle size distribution D50 is 15-45μm.

[0039] The present invention provides a method for operating a three-stage composite kiln for preparing spherical alumina as follows:

[0040] The alumina raw material is fed into the infrared preheating section 1 of the pretreatment unit through the feed inlet 5. It is kept at a temperature of N minutes in the furnace of the infrared preheating section for surface activation treatment. After pretreatment, the alumina raw material enters the microwave oven body of the microwave medium-high temperature phase transition section of the crystal phase transformation section through the first microwave energy suppressor 4. After being kept at a set temperature in the microwave oven body of the microwave medium-high temperature phase transition section for n minutes, the phase transformation of the alumina particles is completed. Then, the alumina particles enter the plasma heating section of the spherical shaping section through the second microwave energy suppressor 7. Under the action of airflow, the alumina particles pass through the plasma flame at a certain flow rate. The molten particles are spheroidized in the turbulent field and separated by the cyclone separator 33 and collected through the discharge port 6.

[0041] Example 2

[0042] This embodiment provides a method for operating a three-stage composite kiln for preparing spherical alumina, taking γ-Al2O3 raw material with a particle size of 5-50 μm as an example. The method is as follows:

[0043] γ-Al2O3 raw material with a particle size of 5-50 μm is fed into the infrared preheating section 1 of the pretreatment unit through the feed port 5. It is kept at 700℃ in the furnace of the infrared preheating section for 30 minutes for surface activation treatment. After pretreatment, the material enters the microwave oven body of the microwave medium-high temperature phase transition section of the crystal phase transformation section through the first microwave suppressor 4. It is maintained in the microwave oven body of the microwave medium-high temperature phase transition section at 1400℃ for 15 minutes to complete the phase transformation of alumina particles. Then, the alumina particles enter the plasma heating section furnace body through the second microwave suppressor 7. Under the argon gas carrier, it passes through the 1800℃ plasma flame at a flow rate of 10 m / s. The molten particles are spheroidized in the turbulent field and separated by the cyclone separator 33 and collected through the discharge port 6.

[0044] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A three-stage composite kiln for preparing spherical alumina, characterized by, It includes an infrared preheating section, a microwave high-temperature phase-inversion section, and a plasma heating section that are sequentially sealed and connected. The microwave high-temperature phase transition section and the infrared preheating section are connected by a first microwave energy suppressor, and the microwave high-temperature phase transition section and the plasma heating section are connected by a second microwave energy suppressor to protect the safety of the equipment operators; the infrared preheating section, the microwave high-temperature phase transition section and the plasma heating section connected in sequence form the main body of a three-section composite kiln for preparing spherical alumina; The infrared preheating section serves as a pretreatment section for drying and dehydrating alumina raw materials; the microwave high-temperature phase transformation section serves as a crystal phase transformation section, using microwave radiation to transform alumina from the γ phase to the α phase; and the plasma heating section serves as a spherical shaping section, using an air-suspended turbulent flow field to spherically shape molten alumina particles. The air-suspended turbulent field is formed as follows: the plasma torch at the bottom of the plasma heating section generates a high-temperature, high-speed airflow, which enters the shaping cavity of the spherical shaping section from bottom to top, forming a gas flow region with rotational and turbulent characteristics in the upper space of the shaping cavity, thereby forming an air-suspended turbulent field; the molten alumina particles entering the gas flow region remain suspended and continuously tumble under the action of the airflow, and gradually shrink and form spherical particles under the action of surface tension.

2. The three-section composite kiln for preparing spherical alumina according to claim 1, characterized in that, The infrared preheating section includes an infrared preheating section furnace body, a K-type thermocouple, and a high-purity alumina crucible. The infrared preheating section furnace body is equipped with a feed inlet and an exhaust outlet. An insulating sleeve is fixedly fitted over the outside of the infrared preheating section furnace body. A distributed infrared heat source is installed inside the insulating sleeve to uniformly heat the infrared preheating section furnace body. The K-type thermocouple is installed inside the furnace chamber of the infrared preheating section furnace body and is positioned corresponding to the material at the bottom of the furnace to monitor the temperature of the furnace chamber. The high-purity alumina crucible is installed inside the furnace chamber. The outlet of the infrared preheating section furnace body is connected to the microwave high-temperature phase transition section via the first microwave energy suppressor.

3. The three-stage composite kiln for preparing spherical alumina according to claim 2, characterized in that, The microwave high-temperature phase transition section includes a microwave oven body and a distributed magnetron system. The distributed magnetron system includes multiple magnetrons arranged in an array on the outer wall of the microwave oven body and connected to the outer wall to transform alumina from the γ phase to the α phase. The inner wall of the microwave oven body is covered with a high-purity alumina ceramic liner. The inlet of the microwave oven body is connected to the outlet of the infrared preheating section through a first microwave suppressor, and the outlet is connected to the plasma heating section through a second microwave suppressor.

4. The three-section composite kiln for preparing spherical alumina according to claim 3, characterized in that, The microwave oven body of the high-temperature phase transition section is equipped with armored thermocouples and an infrared temperature measurement module to measure the phase transition temperature of the alumina material in the high-temperature phase transition section.

5. The three-section composite kiln for preparing spherical alumina according to claim 4, characterized in that, The plasma heating section includes a plasma heating section furnace body, a plasma generator, and a feed inlet disposed on the plasma heating section furnace body; the feed inlet is connected to the second microwave energy suppressor; the plasma generator is disposed at the bottom of the plasma heating section furnace body to heat and ionize the gas to achieve melting of alumina particles and dispersion of gas flow; The plasma heating section furnace body is provided with an airflow cooling furnace chamber; the plasma heating section furnace body is connected to a tangential air intake system, which is used to introduce gas into the airflow cooling furnace chamber so that the alumina particles move from bottom to top; the top of the plasma heating section furnace body is connected to a cyclone separator, which is used to cool and separate the alumina particles.

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